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Home My WebLink AboutAppendix C. Exhibit 3 Gorsuch Engineering ReportGorsuch Haus Project-Planned Development Detailed Review March 2, 2020 Engineering Report for Gorsuch Haus Project Planned Development Detailed Review Submitted To: City of Aspen Engineering Department 201 N. Mill Street, Ste. 203 Aspen, CO 81611 Prepared by: Sopris Engineering, LLC 502 Main Street Suite A3 Carbondale, Colorado 81623 SE Project Number: 15101.06 March 2, 2020 Gorsuch Haus Project-Planned Development Detailed Review March 2, 2020 Table of Contents A. Purpose of Report ....................................................................................................................................... 2 B. Background ................................................................................................................................................. 2 C. Project Summary......................................................................................................................................... 2 D. Site Utilities ................................................................................................................................................. 3 E. Emergency Access & Staging ..................................................................................................................... 7 F. Grading ....................................................................................................................................................... 8 G. Drainage Analysis ....................................................................................................................................... 8 H. Conclusion ................................................................................................................................................ 18 I. Attachments .............................................................................................................................................. 19 Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 2 | P a g e A. Purpose of Report This Engineering Report has been prepared in support of a Planned Development Detailed Review Application for the proposed development of the Gorsuch Haus Lodge located at the southern end of S. Aspen Street within the City of Aspen. The information within this report presents our summary of the engineering analysis and findings to include serving the project with required utilities, evaluating conceptual stormwater mitigation recommendations, conceptual grading design as well as emergency access/staging for the project. Conceptual Civil Design drawings and the corresponding Subdivision Plat are referenced throughout this report and are included within the overall Project Detail Review Application. Designs and associated civil plan sets will be further progressed as the project moves through the approval process with final designs and plans be submitted in support of future building permit. B. Background The Gorsuch Haus Project is a proposed mixed use lodging development proposed at the southernmost end of S. Aspen Street where the existing Lift 1A ski lift resides. The project has gone through several design iterations over the years. Initially it included a skier return corridor with a relocated lift onsite however in 2017 City Council instructed the applicant to work with the Lift One Lodge development team, a separate mixed use lodging project located just north of the Gorsuch Haus Project, and the City to determine if there was a way to bring the lift further down the mountain and closer to Dean Street; in line with the historic lift alignment. The City’s recent land acquisition of the Dolinsek parcel also played into the planning of bringing the lift further down the mountain by providing the required space at the bottom of the ski run to facilitate snow operations at the skier return terminal. After several months of design iterations an acceptable lift re-alignment was selected that worked for all stakeholders and collectively the projects are now referred to as the Lift One Corridor Plan. In 2018 the Gorsuch Haus team and Lift One Lodge team went through the City’s Project Review process separately and with City collaboration, to demonstrate overall mass and scale of the projects as well as how the projects, with the Dolinsek Garden improvements, would be integrated to achieve bringing the lift further down the mountain and provide a safe skier return corridor. After numerous outreaches, stakeholder, Planning/Zoning and Council meetings, City Council referred the projects to voters and in March of 2019 the public approved both projects through separate ordinances. For the Gorsuch Haus project this meant approval, with conditions, for rezoning, Project Review, Subdivision, Growth Management Quota System, Commercial Design, 8040 Greenline, Special Review, Mountain View Plan, Special Review for Lodge Density, Special Review for Affordable Housing Net Livable Standards, and Vested Rights as outlined within Ordinance 39, Series 2016. C. Project Summary The Gorsuch Haus project requires subdividing four existing parcels, currently owned by Aspen Ski Company, into two new lots (Lot 1 & Lot 2) and vacating portions of the City’s right-of-way as well as dedicating right-of- way as further described below and as identified within the Subdivision Plat included within the application. Lot 1 will contain the mixed use lodge with amenity areas to include 81 lodge units, 4 free market units, commercial leasable space, 56 parking spaces, 1 affordable housing unit, terraces, walkways, stairways and an underground parking structure. In addition, this lot requires rezoning from Conservation Zone District to Lodge Zone District. Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 3 | P a g e Lot 2 includes the remaining portion of the subdivided land and will be retained by Aspen Ski Company to facilitate the skier return corridor and lift alignment. It will also include the newly aligned Mountain Access Road, relocated electric recloser and switch gear cabinets, new transformer to serve the Gorsuch Haus Lodge as well as re-aligned utilities that are serving some of Aspen Ski Company’s existing infrastructure located further up the mountain. Lot 2 will remain in the Conservation Zone District. The project also consists of vacating portions of city right-of-way as well as dedicating right-of-way to the City. Through the redesign efforts, in support of getting the ski lift through the project and further down the hill, the Gorsuch building had to shift further to the west which triggered the request to vacate the easterly half of S. Aspen Street. In addition, the project includes the construction of a City compliant cul-de-sac at the end of S. Aspen Street which will serve as a formal terminus point for S. Aspen Street, emergency access/staging as well as the main entrance to the lodge. To facilitate the construction of the cul-de-sac the project includes dedicating portions of the private property to the City as right-of-way. D. Site Utilities Coordination with the various utility providers has taken place to verify layouts, existing utilities, routing and feasibility of serving the proposed project. It should be noted that recent utility improvements along S. Aspen Street were installed in support of the S. Aspen Street Townhomes project which is located north of the subject property and along the west side of S. Aspen Street. It should also be noted that the improvements anticipated future development of the Gorsuch Haus and Lift One Lodge projects and include a new 16” water main, sanitary sewer main, storm drain system and primary electric, telephone and cable infrastructure. Our findings and proposed utility infrastructure required to serve the project are discussed further below: Water The project falls within the City of Aspen’s service area. As noted above, a new 16” water main was recently installed along S. Aspen Street. The approved construction drawings actually included the extension of the water main to continue east along Hill Street and re-connect to the existing system just east of S. Monarch Street. However, prior to this section being installed it was determined that the proposed alignment might create complications to the Lift One Lodge and Gorsuch Haus Projects and therefore the City agreed to defer the final 500+ feet until after revised site plans for the Gorsuch and Lift One Lodge projects were available to determine if a better alignment could be provided. As such, the recent site revisions associated with the Gorsuch Haus Project provides an opportunity to improve the previously proposed alignment for this final section of water main. The proposed re-alignment and design are illustrated within the Civil Plan Set (C.3.03 & C.3.04) included with the application. In summary, the 16-inch water main extension runs down the center of the remaining Hill Street ROW which is 25-ft in width. A utility easement is being provided along the northern portion of Lot 1 that will provide a total width of 30-ft for any future maintenance needs and to adhere to the City of Aspen’s Water Standards. As the proposed water main enters Lot 2 a 30-ft easement is also provided for future maintenance and access of this water main. Once the new water main leaves Lot 2 it will fall within the existing 20-ft easement (Bk. 411 Pg. 996) that runs along the north side of the Mountain Queen townhomes and then re-connects east of S. Monarch Street within the City’s right-of-way. A high point has been provided that coincides with the fire hydrant located at the northwest corner of S. Monarch and Summit Street. This high point was derived to avoid adding an air release valve or an additional fire hydrant at the topographical high point. Consequently, the 16” water main requires additional bury depth Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 4 | P a g e (14-ft max) beyond the 10-ft max. bury depth typically allowed. This has been discussed and approved with City Engineering and Water Department. In the end, the re-designed 16” water main from S. Aspen Street to Summit Street has an improved alignment as compared to the previously approved construction drawings. It avoids conflicts with structures, reduces the amount of bends and provides additional separation between proposed structures and existing trees which improves future access and maintenance to the water main. Further coordination with the City Engineering and the Water Department are anticipated as the project design progresses to further evaluate sequencing and means/methods of installing this remaining portion of 16-inch water main while minimizing the impacts to the City’s current customers. According to conceptual estimates performed by the project’s plumbing engineer the project has an estimated domestic demand of 760 water supply fixture units which equates to about 180 gpm average demand. In addition, preliminary fire suppression anticipates an additional 385 gpm. Based on this information the project is anticipating a combined domestic/fire water service size of 6-inches. This combined fire and domestic water service will be tapped from the new 16” water main. Given the multiple utilities passing through the area and conceptual horizontal and vertical design of this water service vertical bends are anticipated. This has been discussed and approved by the City Engineering and Water Department. Lastly, since the development extends above the City’s 8040-Greenline a private water pressure boosting system will likely be required to ensure adequate pressures and fire flow requirements are maintained. Final designs of the extended water main, booster pumps, service lines and fire suppressant systems will be provided at time of building permit application. Additional water improvements includes re-connection of Mountain Queen’s water services which are currently tapped from an existing 6” cast iron water main that runs parallel to the existing 12” water main and within the prescribed easement (Bk 411 Pg 996) located north of the Mountain Queen building. This 6” water main also services an existing fire hydrant located along the west side of the Mountain Queen townhomes. According to our discussions with Aspen Fire they would prefer to disconnect the hydrant line from the City’s water system and simply provide a separate dry hydrant line consisting of a 3-way fire department connection riser located near the existing fire hydrant at the northwest corner of Monarch St & Summit Street intersection. This dry line would then run parallel to the 16” water main and extend along the west side of the Mountain Queen building and within the existing fire access easement (Bk. 275 Pg 378) that resides on proposed Lot 2. Additional fire department connections with valves are proposed along the west side of the Mountain Queen as illustrated on Civil Plan C.3.04. This will vastly improve the existing condition by negating the need for any vehicular fire access along the west side of the building. Instead, Aspen Fire personnel will simply be able to park a fire truck at the end of S. Monarch Street and connect a hose from the existing fire hydrant at the northwest corner of the intersection to their truck and then to the proposed riser pipe which will then supply the proposed dry hydrants with fire flows. Aspen Fire personnel will then need to carry fire hoses up to the proposed dry hydrants and won’t need to get a fire truck up the seasonal access road. It should be noted that portions or all of the existing 6” water main intended to be re-purposed as a dry feeder line to the three hydrants might require re-alignment and/or complete replacement given the age and material of the existing line. Additional coordination with City Engineering, Aspen Fire, Water Department and Mountain Queen Townhomes is anticipated as the design progresses. Final designs will be provided at time of building permit application. Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 5 | P a g e Sanitary Sewer Aspen Consolidated Sanitation District (ACSD) is the supplier of sanitary sewer service to the subject property and surrounding area to include Ruthie’s Restaurant located further up the mountain. According to preliminary estimates performed by the project’s plumbing engineer the anticipated sewer demand for the project is estimated to be 808 drainage fixture units (DFUs). Since there isn’t a direct conversion from DFUs to gallons per minute (gpm) the estimated peak domestic water demand of 178 gpm has been used for preliminary sanitary sewer peak flow estimates. This is appropriate since this type of use/buiilding typically results in a mass balance of “water in” roughly equal to “waste out”. Further analysis of the peak sanitary sewer demand will be performed and coordinated with Aspen Sanitation District as the project design progresses. The project is currently proposing on single point of exit from the building which will require an 8-inch sanitary sewer service. Currently the service is proposed to extend from a new manhole installed at the terminus end of the District’s mainline that runs up S. Aspen Street. An additional manhole is proposed within the center of the island to provide a point of connection for Ruthie’s relocated sewer service discussed further below. From this point the sewer service will extend to the building. Grease interceptors will be provided for any and all commercial food processing establishments and a sand/oil interceptor will be provided within the proposed parking garage. Ejector pumps are anticipated for portions of the project given the elevations of the parking structure. Abandonment of all existing sewer services shall comply with ACSD specifications and be performed prior to commencement of any shoring activity. Final terminations will need to be inspected by ACSD personnel. In addition to the proposed sanitary sewer service discussed above it was determined that the 8” private sanitary sewer service serving Ruthie’s Restaurant further up the mountain falls within the proposed building footprint and therefore a realignment of this private service is also required as part of this project. A conceptual alignment and profile are provided within the Civil Plan set included within the Detail Review Application. Essentially, the proposed private service alignment will extend from a shared manhole located within the proposed cul-de-sac island and then essentially follow the re-aligned Mountain Road before reconnecting south of the proposed building. As noted above, a portion of this private service line will also serve the Gorsuch Haus Lodge which will require either a shared service agreement or an extension of the District’s mainline by approximately 40-ft to the east as illustrated on sheet C.3.00 of the civil plan set. This has been discussed with Aspen Consolidated Sanitation District and it is our understanding that this can be determined at a later date. All work associated with Aspen Consolidated Sanitation District infrastructure shall be in accordance with their rules and regulations. An ability to serve letter has been attached to this report. Electric Holy Cross Energy is the supplier of electric service in this area. Numerous coordination meetings have occurred to better understand the improvements that were installed along S. Aspen Street and how to best serve the project. This section outlines the existing infrastructure as well as the proposed electrical improvements required in support of this project. As part of the S. Aspen Street recent utility improvements new primary electric lines were installed from a new electric splice vault located at the intersection of S. Aspen Street and Durant Avenue up to an Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 6 | P a g e existing splice vault located just northwest of the existing Lift 1A terminal. This primary run of electric lines along S. Aspen Street feed a couple of existing transformer located on Lift One Lodge’s property, S. Aspen Street Townhomes, Shadow Mountain Townhomes, a recloser cabinet, a switch gear, Lift 1A as well as additional existing facilities serving Aspen Ski Company located further up the mountain. The proposed improvements associated with the Gorsuch Project will require relocating the existing re- closer located near Lift 1A as well as the recently installed switch gear located just northwest of the proposed Lodge building. Furthermore, the existing primary line that feeds infrastructure further up Aspen Mountain will need to be re-routed to accommodate the proposed building. The anticipated electric service demand for the project is a 5000 amp 208V service. Based on discussions with Holy Cross Energy this service can be provided via a single 1500 kva three phase transformer. The proposed location of the transformers to serve the project and the relocated recloser and switch gear is along the east side of the building and outside the proposed ski way as illustrated on sheet C.3.00 of the Civil Plan Set. The proposed layout adheres to Holy Cross’s required separations and clearances. The access doors for the switch gear are positioned at the north and south sides. The recloser and transformer doors will face to the east. The primary electric run will continue further to the south through Lot 2 and re-connect to an existing splice vault that services an existing transformer located further up the mountain (transformer #3128P3). An intermediate splice vault is anticipated given the length of the primary run. Additional infrastructure will include an antenna that will serve the recloser and switch gear. The antenna will need to be installed such that it has a clear line of sight to the receiving antenna located further up the mountain near “Kleenux Corner”. In addition to the electrical improvements mentioned above there will be a considerable amount of cut required to accommodate the proposed cul-de-sac at the end of S. Aspen Street which will result in some retaining walls. Consequently these retaining walls will prohibit access to Shadow Mountain’s existing transformer (3128P1) and therefore the design team has been working on solutions to mitigate this condition. The current plan is to re-establish secondary service to the Shadow Mountain Townhomes from the recently installed transformer located at the southern end of S. Aspen Street Townhomes (transformer #3130P2). The design team’s electrician has performed initial site investigations to evaluate Shadow Mountain’s existing secondary electric service and has determined that a new secondary feed can be provided from the existing transformer located near S. Aspen Street Townhomes (3130P2). The secondary feed will extend from this transformer and re-connect to Shadow Mountain’s existing meter panel which is currently located adjacent to their existing transformer that is currently providing service. Once this secondary service has been re-established the existing transformer serving Shadow Mountain Townhomes can be abandoned thereby eliminating any future access concerns. This has been presented and determined to be acceptable by Holy Cross Energy. Further coordination with Holy Cross Energy, Shadow Mountain Townhomes and S. Aspen Street Townhomes is anticipated as the design progresses. A will serve letter from Holy Cross has been provided as an attachment to this letter. Gas Black Hills Energy is the provider of natural gas in the area. As part of the recent S. Aspen Street utility upgrades a new 6” gas main was extended to the southern end of S. Aspen Street. This main provides service to Shadow Mountain Townhomes as well as Ruthies Restaurant located further up Aspen Mountain. The anticipated gas demand for the project has been estimated at 16,240 MBH and based on discussions with Black Hills Energy the new 6” gas main has adequate capacity to serve the project. The Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 7 | P a g e size of the proposed service will be determined prior to building permit. The location of the proposed meter to serve the project is located along the east side of the building. It will be served from an extended gas main that will follow the re-aligned Mountain Road and re-connect to the existing gas main that serves other infrastructure further up the mountain. In addition, the project includes re-routing Shadow Mountain’s existing gas service which currently falls under the proposed building. This will be accomplished by extending a new service line from the recently installed 6” gas main located at the southern end of S. Aspen Street. The service will run along the west side of the project and fall within the remaining S. Aspen Street right-of-way. All natural gas improvements/infrastructure shall conform to Black Hills rules and regulations and a will serve letter has been attached to this report. Telephone CenturyLink is the provider of telephone service within the area. New service to the proposed building will be extended from the recently installed main line infrastructure that was installed as part of the S. Aspen Street improvements. In addition, re-routing of existing telephone service feeds currently serving infrastructure further up the mountain is anticipated to accommodate the construction of the proposed building. The re-alignment of this main line will follow the re-aligned Mountain Road and re-connect south of the proposed building with a splice vault. A couple of pull vaults are anticipated given the length of run that is being considered. All work related to telephone service shall be installed per Century Link’s rules and regulations and a will serve letter has been attached to this report. Cable & Fiber Optic Comcast is the provider of cable service within the area. New service to the proposed building will be extended from the recently installed main line infrastructure that was installed as part of the S. Aspen Street improvements. Comcast also has a fiber optic pedestal located along the north side of Dean Street. Fiber optic service can be extended from this pedestal if fiber optic is required for the project. All work related to cable and fiber optic service shall be installed per Comcast rules and regulations and a will serve letter has been attached to this report. Further coordination and refining alignments of primary and secondary utility lines may occur as the project progresses with final designs being provided in support of future Building Permit Application. E. Emergency Access & Staging The new site plan includes a cul-de-sac at the end of S. Aspen Street that will serve as the primary pick up/drop off and access to the site as well as emergency turn around. This cul-de-sac will be dedicated to the City as ROW and meets their minimum dimensional requirements as stated within Title 26.580.020 of the City of Aspen’s Land Use Code as well as Section 4.2.3 of the City’s Engineering Standards. The cul-de-sac also provides 23-ft of width for one-way vehicular circulation as well as a 12.5 ft wide drop off aisle which will provide primary ADA access to the property. Furthermore, extensive coordination with Jensen Hughes and Aspen Fire has taken place to develop a Fire Staging Plan as illustrated on sheet C.1.03 within the Civil Plan Set. The result of the new cul-de-sac will improve the current condition. It will create a formal turnaround area Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 8 | P a g e at the end of S. Aspen Street which doesn’t exist today and complies with City of Aspen Standards. It will also limit the potential conflicts with vehicles and pedestrians by providing formal crossings as well as a pedestrian corridor around the entire perimeter of the cul-de-sac. F. Grading Extensive grading is proposed throughout the project to facilitate the cul-de-sac, skier return corridor, new mountain access road, and construction of the proposed lodge. In addition, an offsite swale (West Swale) is proposed along the west side of the building. The swale is constrained along the east side by the proposed lodge and along the west side by existing improvements and steep hillside slopes. Consequently, there is a short section of grading that will require 1:1 slope to daylight back to the existing hillside. The conceptual plan includes reinforcing the slope with erosion control mats, boulders and/or gabion baskets. The design of this hillside stabilization will be further evaluated as the project design progresses towards Building Permit. A variance request from the City’s design standards will be required if 1:1 slopes are determined to be the best grading solution for this area. If a variance is required it will be provided after final grading designs and associated details have been prepared. It should also be noted that there are several areas located within Lot 2 that will result in 2:1 daylight slopes. These areas are limited to the cut/fill slopes associated with establishing the new Mountain Road alignment to help minimize overall disturbance. The design and associated slopes have been reviewed and approved by Aspen Ski Company who will ultimately be responsible for maintaining these areas. These areas will be protected and re-vegetated with detailed plans being provided in support of a future building permit. G. Drainage Analysis (a) Introduction The intent of this Section is to provide background drainage information of the subject property, describe the existing onsite and offsite drainage conditions as well as to provide conceptual stormwater mitigation solutions, with a strong emphasis on offsite stormwater routing and water quality treatment. This analysis will be expanded as the project design progresses with final designs, drainage report and details being provided in support of any future Building Permit Application. (b) Background & Overview The subject property falls within System 3 as described within the Surface Drainage Master Plan (SDMP) for the City of Aspen, dated November 2001 prepared by WRC Engineering, Inc. Based on figure ES-4 of this report this System appears to have capacity to convey a runoff event with a magnitude between a 10-year and 50-year storm event; however it also indicates that the combined capacity of the street and storm sewer along S. Aspen Street appears to have sufficient capacity to convey the 100-year runoff event. It should be noted that the SDMP study was based on previous NOAA rainfall data (NOAA Atlas 2) and that more recent data has since been released (NOAA Atlas 14) that carries 40 more years of rainfall records. This new data shows upwards of a 35% reduction in rainfall depths as compared to previous information and therefore the previous conveyance capacities now coincide with a larger storm event. Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 9 | P a g e According to FEMA Flood Insurance Rate Map panel number 08097C0362E, with an effective date of 08/15/2019, the property falls entirely within the Zone X flood hazard area. FEMA designates Zone X as areas outside the 0.2% (500 year storm) annual chance floodplain. SE reviewed two drainage reports prepared for adjacent development. SGM prepared a Drainage report for Lift One Lodge, dated January 2013, which is the proposed development directly north of the site. SGM also prepared a drainage report for South Aspen Street Townhomes, dated August 2014, which is the recently constructed development across S. Aspen Street northwest of the site. The offsite basin delineation, analysis methods, and peak flows were reviewed and are consistent with the site drainage analysis outlined herein. The project falls within City of Aspen mudflow hazard zone which requires a mudflow analysis. Tetra Tech prepared the Gorsuch Haus Mudflow Analysis report dated January 13, 2020 which has been included with the Project Detail Review Application. The Tetra Tech study identifies two sources of debris flow surrounding the proposed development. It also provides mitigation recommendations that are identified on C.2.07 of the civil plan set which are also included with the Project Detail Review Application. In addition, Tetra Tech provided our office with split clear water flows associated with Pioneer Gulch that get conveyed towards the proposed development which we have included in our offsite storm water flow analysis. It should be noted that this additional flow was not reflected in previous drainage studies noted above. The Pioneer Gulch storm flow is discussed in more detail in section C below. (c) Existing Drainage Conditions The subject property (not including the proposed right of way area) encompasses approximately 44,526 square feet. The existing site includes a portion of the ski hill lift building and structures, gravel parking areas, and the existing ski run hillside. The existing onsite drainage basin is approximately 50,915 square feet (sf), which includes the site as well as the southern end of the S. Aspen Street right of way area. An analysis of the existing conditions survey and information gathered during multiple site investigations produced no evidence of large scale drainage structures for detention or water quality improvements for the majority of the subject property. The existing site has approximately 20,905 sf of impervious area, of which 14,692 sf are gravel parking and road areas. This produces a 41% impervious site resulting in immediate conveyance of stormwater into the City’s right-of-way, without the benefit of water quality treatment. Despite this lack of onsite stormwater infrastructure no evidence of flooding was observed during the several site visits. Overall storm water conveyance is towards S. Aspen Street. The north end of the existing basin includes a shallow swale and storm inlet that captures runoff into the storm sewer in S. Aspen Street. An existing inlet recently installed in support of the S. Aspen Street Townhomes project located along the northwestern extents of the project area captures storm water runoff from the hillside into the existing storm sewer on the west side of S. Aspen Street. The development parcels on the west side of S. Aspen Street have separate drainage systems and are not included in our drainage analysis. The existing basins are described below, and are shown on sheet C4.00. Offsite Basin EX-01 is the western offsite basin and includes a portion of Basin 9 as described within the City’s SDMP, which consists of the steep existing hillside south and west of the site. The basin extends up to the ridge on the west side of Aspen Mountain. The hillside includes native forested hillside as well as open ski run area that are fairly steep with grass ground cover. Runoff generated from this basin is conveyed to the existing inlet on the west side of the site which is design point (DP) #J-01. Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 10 | P a g e Offsite Basin EX-02 is the small central offsite basin that falls within Basin 20 as described within the City’s SDMP. The hillside includes native forested hillside and open ski run area. Similar to basin EX-01, the forested hillside is well vegetated, and the open grass areas are moderately well vegetated. Runoff is conveyed on the surface and along the existing Mountain Access Road toward S. Aspen Street where flows are then collected within a series of curb inlets. We have designated this collection point as design point #J- 02. Offsite Basin EX-03 is the small eastern offsite basin that falls within the northern boundary of Basin 20 as described within the City’s SDMP. The hillside is primarily open ski run area. The hillside is moderately vegetated grasslands. The basin is bound on the eastern end by the existing Mountain Queen townhomes. The eastern end of the basin has an existing gravel access road with a moderate low point which includes an existing storm inlet / drywell. The storm inlet conveys runoff to a second existing drywell structure, and then daylights within the existing swale located just north of Hill Street ROW. There is an existing inlet at the west side of the swale that connects to the S. Aspen Street storm sewer system. Based on existing conditions survey information this inlet lies just north of the Hill Street ROW and within the Lift One Lodge’s property. The initial inlet is designated as design point #J-03 and the connection point to the S. Aspen Street system is identified as DP J#02. The inlet located on Lift One Lodge’s property (#J-03) will be removed as part of the project improvements. Offsite Basin Ex-04 is the Pioneer Gulch drainage basin. The basin is modeled in the Tetra Tech mud flow analysis. As mentioned in the overview section above, the basin flow splits around the Mountain Queen structure. Per information provided by Tetra Tech, the 10 year peak clear water flow is 0.5 cfs, and the 100 year clear water peak flow is 13 cfs. We have modeled the clear water portion of the split flow in our drainage analysis. This split flow follows the same flow path as storm water generated from basin EX-03 described above. Offsite Basin Ex-OS5 includes the Shadow Mountain Townhomes area. Stormwater flows are routed through the site and are intercepted at a recently installed inlet (Inlet OS5) located along the north side of Shadow Mountain’s drive access off S. Aspen Street. This inlet will remain and continue to serve Shadow Mountain as it currently does under existing conditions. (d) Developed Drainage Conditions The proposed post developed onsite and offsite basins are shown on Sheet C4.01 of the civil plan set. With development, offsite basin EX-02 is now routed around the site improvements. A portion of EX-02 is now included in proposed offsite basin Post OS1 and Post OS3, and the onsite developed basins. The developed basins are described below. Offsite Basin Post-OS1 is the western offsite basin and includes EX-01and the upper western portion of EX- 02. Aside from grading improvements adjacent to the proposed lodge the basin conditions do not change with development and the area will continue to serve as a ski corridor with vegetated ground cover. Improvements within this basin include the lodge building, the construction of the “West” swale and relocating the existing inlet (DP J-01) to the south by approximately 20-ft to accommodate the construction of the proposed cul-de- sac and associated site retaining walls. Runoff from this basin will be conveyed to the relocated inlet (J-Inlet Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 11 | P a g e #3) which will include concrete wing walls and resetting the grate from the previous inlet structure. The construction of the “West” swale will include erosion control protection. Further design and detailing of this swale will be provided in support of future building permit applications. Offsite Basin Post-OS3 is the small eastern offsite basin and includes EX-03 and the upper eastern portion of EX-02. The proposed improvements include overlot grading and the construction of the re-aligned Mountain Access Road. This basin was broken into four sub-basins in support of conceptual sizing storm inlets and pipes as further described below: Post OS3.1: Includes the northern portion of the Mountain Road and ski way. Flows from this basin are conveyed over the surface and/or along the Mountain Road’s ditch to a proposed manhole located within a low point. The manhole will have an open grate to also serve as a sump inlet. Post OS3.2: Lies just south of OS3.1 and encompasses the area between the proposed lodge and re-aligned Mountain Road. Runoff from this basin will be conveyed towards a proposed on-grade inlet (Inlet #6) located within the Mountain Road’s ditch. Flows that exceed the capacity of this on-grade inlet will continue through Post OS3.1’s drainage basin and ultimately collected within the MH-D sump inlet located within a depressed area further to the north. Post OS3.3: Encompasses the area between Mountain Queen and the new Mountain Road. Flows from this basin will follow existing drainage patterns towards a proposed sump inlet (Inlet #7) located along the east side of the Mountain Road and just south of Mountain Queen’s existing fire access road. This inlet will also intercept split flows generated from EX-04. Post OS3.4: Includes the area south and east of the lodge and west of the re-aligned Mountain Road. Runoff generated from this basin will be routed within the proposed roadside swale associated with the Mountain Road towards a proposed on-grade inlet (Inlet #8). Flows that exceed the capacity of this inlet will be conveyed further down the roadside swale towards Inlet #6 located within Post OS3.2. The proposed storm sewer system associated with Post OS3 will be considered private, owned and maintained by Ski Co, until it connects to MH-C which which is a proposed extension of the City’s storm system and located within Hill Street ROW. This proposed storm system was designed to maximize intercepting capacity of site runoff which thereby reduces the erosion in the roadside swale as well as further conveyance of offsite runoff through the proposed Lift One Lodge site. S. Aspen Street Post-Basin includes portions of the proposed cul-de-sac to include the center island. A small area inlet is proposed within the center of the cul-de-sac to help prevent snowmelt from draining across the cul-de-sac and to mitigate nuisance runoff from the landscape island. The proposed area inlet within the island is a 6-inch Nyloplast area inlet with a 6-inch conveyance pipe. Runoff generated from the majority of the cul-de-sac drive lanes will be routed to the relocated curb inlets at the southern end of S. Aspen Street. It should be noted that the peak tributary areas conveying runoff to these inlets will be drastically reduced as compared to existing conditions since the majority of runoff will now be collected by the proposed offsite stormwater infrastructure. Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 12 | P a g e Onsite Developed Basin: For this conceptual stormwater mitigation analysis the onsite basin delineation consisted of the areas that will include water quality treatment of stormwater runoff which primarily includes proposed roof, patio, plaza and stairwell areas as well as some portions of the right-of-way. Of these areas the majority of them fall above structure which will require internal routing of drain lines. Since the design of this internal routing system has not been completed some assumptions were made on where and how runoff will be routed for stormwater treatment. These assumptions were based on our initial coordination with the plumbing engineer, architect and our review of proposed downspout locations and the design of the roof. This coordination and evaluation resulted in the development of two onsite basins as further described below. Further coordination is anticipated with the architect and plumbing engineer as the design of the internal drainage system progresses with final designs being provided in support of a future building permit. DE-01 includes the northern portion of the lodge, the plaza along the north side, the west stairwell and associated patios that fall outside roof line as well as approximately 1,500 sf of right-of-way associated with portions of the plaza and cul-de-sac. Currently, runoff from this basin is assumed to be routed to the “West” water quality treatment vault as further described below. Various area inlets are anticipated and conceptually laid out for the west stairwell and adjacent patios. These area inlets primarily fall outside the limits of below grade structure and therefore will be routed to the proposed “West Onsite Storm” piping system that is currently proposed to extend along the entire west side of the lodge. Runoff from the portion of the main entrance and north plaza area that fall above below grade structure will be routed to area inlets and/or trench drains that will need to be routed internally and ultimately terminate within the “West” water quality treatment vault. Stormwater runoff generated from portions of the cul-de-sac and private drop off area will be routed to a proposed valley pan inlet located along the west side of the private drop off area. Runoff generated from the remaining onsite plaza area as well as some portions of the plaza that fall within the right-of-way will sheet flow over the surface and get collected within a slot drain proposed along the top back of mountable curb or the trench drain located at the top of the pedestrian ramp. DE-02 includes the remaining portion of the onsite improvements located on Lot 1. The majority of this area consists of roofs, terraces and patios that all fall above structure and therefore internal routing of the corresponding inlets and drainage infrastructure will be required. An exterior storm drain is proposed to run up the entire east side of the building to accommodate downspouts and exit points for internal drainage pipes. Again, internal roof routing within the building has not yet been completed. Therefore, the proposed basins described above will likely require adjustments as the design progresses. In addition, proposed basins DE-01 and DE-02 were considered to be 100% impervious for this conceptual analysis. With this said, the amount of required water quality treatment volume is not expected to increase from this preliminary estimate. (e) Hydrologic Methods and Assumptions The drainage criteria used for this study was based on the COA’s URMP dated December 2014 with supplemental information taken from Urban Drainage Flood Control District Manual (UDFCD). The improvements associated with this project classify it as a “Major Design” which requires an analysis for the 10 and 100-year storm events. This section describes the preliminary hydrological assumptions and methods used to estimate the peak runoff rates associated with the 10- and 100-year storm events. Final designs, details, and the drainage report will be provided in support of the future building permit. Refer to the civil Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 13 | P a g e design drawings for illustrational support of the proposed storm water conveyance system and overall grading plan. Peak Runoff rates for the 10- and 100-year storm events were calculated using the Rational Hydrologic Method (Eq. 1) since the cumulative total of basin areas was less than 90 acres. Eq. 1: Q = C* I * A Q = Runoff Flow Rate (cfs) C = Runoff Coefficient I = Rainfall Intensity (in/hr) A= Area of Basin (acres) The runoff coefficient (C) is a variable that represents the ratio of runoff to rainfall volumes during a storm event. The determination of C mainly depends on the soil type, watershed impervious and storm event frequency. Each drainage basin was studied to determine the percent of impervious area, which was then entered into the UD-Rational Spreadsheets (version 2.00) to determine the corresponding 10- and 100-year runoff coefficients. The UD-Rational Spreadsheet was developed by Urban Drainage Flood Control District (UDFCD). The spreadsheet has been adjusted and adopted by the City of Aspen to reflect the local drainage conditions. Tables 1-3 below provide a summary table for the site specific offsite and onsite spreadsheets. The design rainfall duration used in the Rational Method is referred to as the time of concentration. The time of concentration is the cumulative travel time, including overland flow and channelized flow, for runoff to get from the furthest point upstream of a basin to a designated design point. Per COA URMP, 5 minutes was used as the absolute minimum time of concentration. This minimum value was adopted for the smaller basins and sub-basins. Times of concentration for the larger basins were determined using UD-Rational Spreadsheets. The resultant times of concentration and corresponding rainfall intensities were used to estimate the peak runoff rates for each of the basins and sub-basins. A summary of the results for existing offsite, post development offsite, and post development onsite conditions are summarized within Tables 1-3, respectively. Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 14 | P a g e To ensure conservative results, SE also analyzed the offsite basins using the EPA Storm Water Management Model (SWMM), which is a dynamic hydrology-hydraulic water quality simulation model. In the SWMM model, the peak runoff calculated for EX-01 was very close to the rational method peak. The peak runoff in the SWMM was lower for EX-02 and EX-03 when compared to the Rational Method. The Rational Method was used for modeling as it is the conservative model for flows, and it facilitates peak runoff modeling with onsite basins. SE also compared the offsite basin peak flows to the other drainage reports prepared for this area of Aspen. The drainage flows for the offsite basins were also very close to the results outlined above. Lastly, post development basins DE-01 and DE-02 were considered to be 100% impervious despite the proposed landscaping that falls within these basins. This was considered to be a conservative approach and appropriate for conceptual design. The final landscape/pervious areas will be accounted for in the final drainage design. (f) Hydraulic Methods and Assumptions Storm Sewer sizing was achieved by using StormNET Software. StormNET uses the Manning’s equation to compute the flow rate in open channels and partially full closed conduits. HDPE and PVC SDR 35 pipes are proposed for all onsite private storm sewer conveyance pipes, and a Manning’s roughness coefficient of 0.013 was used. Reinforced Concrete Pipe (RCP) is proposed for the main storm sewer pipes located within the City’s ROW, and a Manning’s roughness coefficient of 0.013 was used. The storm pipes have been sized to accommodate the peak runoff rates associated with a 100-year storm event. Where the storm sewer pipe is completely inundated, Hazen-William’s equation was selected in StormNET to analyze the system under pressure conditions. In addition, hydrodynamic link routing was selected. This approach solves the complete St. Venant equations throughout the drainage network and includes modeling backwater effects, flow reversal, surcharging, pressure flow and interconnected ponds. Hydraulic grade lines and energy grade lines were also estimated using StormNET software. StormNet Software calculates the maximum EGLs and HGLs for all structures and storm sewer pipes. It also provides an illustrational depiction within the model’s user interface. Final HGL and EGL information will be provided for final permit plans. Refer to images 1 through 3 below for graphical profiles of the 100 year storm event in the West & East Offsite storm systems. Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 15 | P a g e Image 1: East Storm Sewer-1 Image 2: East Storm Sewer-2 Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 16 | P a g e Image 3: West Storm Sewer The West Offsite Swale has also been modeled in Stormnet. The maximum and minimum longitudinal slopes were considered in the analysis and a roughness coefficient of 0.05 was used with the understanding that the channel will be lined with erosion control protection. The corresponding depths and velocities for the 10-year and 100-year storm events are summarized within Table 4. Table 4: West Swale Summary Sizing of all stormwater mitigation infrastructure will be further evaluated as the project design progresses with final designs being provided in support of a future building permit. (g) Conceptual Drainage Mitigation Summary Since the entire site is anticipated to be disturbed during the construction of the improvements it will be classified as a “Major Design” (> 1,000 sf of disturbance & disturbance greater than 25% of the total lot area) as described within the City URMP. SE discussed the drainage mitigation with the City of Aspen Engineering department during the pre-design discussion meeting. As discussed with the City, the site is directly connected to the City’s storm system, so storm water detention is not required or provided. The project will provide water quality treatment. The drainage mitigation for the site is discussed in the sections below. Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 17 | P a g e Water Quality Treatment: Water quality treatment is required for all projects that disturb more than 200 square feet. The overall goal of the water quality treatment requirements is to protect receiving waters including the Roaring Fork River, Maroon Creek, Castle Creek and tributaries to these water ways. The treatment is provided by strategically incorporating stormwater Best Management Practices into the project’s stormwater infrastructure that are capable of providing full water quality treatment for up to the 80th percentile runoff event which corresponds to the volume of runoff generated from a storm event with a magnitude falling between a 6-month and 1-year. The water quality capture volume associated with these more common storm events is directly correlated to the amount of impervious area within a contributing drainage basin. As discussed in the pre-design meeting with the City, water quality treatment for this project will be provided through the use of subsurface sedimentation/filtration vaults. The conceptual integration of these water quality treatment facilities are discussed below and illustrated on the attached plans. In addition, Table 5 has been provided to summarize the results of this preliminary water quality treatment analysis. Subsurface Sedimentation/Filtration Vaults and/or alternative underground treatment facility will be used. Storm water will gravity flow from the site to the vault, and continue after treatment to the site storm sewer to the S. Aspen Street storm sewer. Further analysis of these structures and exploring additional water quality treatment options will be explored as the design progresses. The storage depth above the filter media will be 3.5-4.0 feet deep and both vaults will gravity flow after treatment to the storm sewer. The location and a conceptual schematic detail of this proposed subsurface sedimentation treatment vault has been provided on C.4.03 of the Civil Plan Set. West WQ vault treats storm water runoff from basin DE-01. As described above, DE-01 is primarily roof and hardscape areas, which includes approximately 1,500 sf of ROW area. This basin was considered to be 100% impervious for this conceptual analysis. Landscape/pervious areas will be included for final designs. The West water quality vault is situated on the east end of the cul-de-sac and will likely encroach into the ROW and therefore a permanent encroachment license will need to be pursued prior to obtaining a certificate of occupancy. As noted above, this treatment vault will also be providing water quality treatment for portions of the ROW. The final drainage and water quality treatment design will provide further details of this structure which will determine the level of encroachment and overall sizing. East WQ Vault treats storm water runoff from basin DE-02, which primarily includes roof and hardscape areas. To be conservative under the conceptual design the entire basin was considered to be impervious. Further evaluation of landscape and pervious areas will be performed and included within the final sizing and design of all water quality treatment infrastructures. Stormwater runoff will be routed to the East structure via drainage pipes routed internally through the building as well as the proposed East Onsite Storm Pipe proposed along the east side of the building. Table 5 summarizes the conceptual water quality treatment volumes for the Lot 1 onsite basins DE-01 and DE- 02. Table 5: Conceptual Water Quality Treatment Summary Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 18 | P a g e The design of the required water quality treatment volumes and associated vaults will be finalized prior to building permit, per final design parameters. H. Conclusion In conclusion utility routing required to serve the redevelopment has been coordinated with the various utility providers and presented on the Civil Plan Set which has been included with the Detail Review Application. Any and all required easements will be provided to the appropriate utility providers at the time of final plat. The proposed cul-de-sac will provide a formalized turn around at the end of the S. Aspen Street which does not exist today and will improve circulation and reduce pedestrian/vehicle conflicts. It will also provide adequate emergency/fire staging area in times of an emergency. The conceptual drainage mitigation design outlined within demonstrates that the project has a viable solution for mitigating offsite and onsite storm water runoff as well as providing water quality treatment for proposed impervious areas. As mentioned throughout this document, final design of all site grading, utilities, site and right-of-way improvements, and proposed stormwater infrastructure will be provided during building permit application. Gorsuch Haus Lodge Development Project-Planned Development Detailed Review March 2, 2020 S OPRIS E NGINEERING • LLC civil consultants 502 Main Street Suite A3 Carbondale Colorado 81623 (970)704-0311 Fax:(970)704-0313 19 | P a g e I. Attachments A. Will Serve Letters B. Storm and Sanitary Analysis Input/Out files Improving life with energy www.blackhillsenergy.com Black Hills Energy 0096 C.R. 160 Glenwood Springs,co.81601 Nov. 12, 2019 Re: Gorsuch Haus Project To Whom It May Concern: This letter will confirm that Black Hills Energy will provide Natural Gas Distribution service to The Gorsuch Haus Project on S. Aspen st. in the town of Aspen, Co. Black Hills Energy will install a distribution system capable of serving the demand of the development that lies within the BHE certificated service territory. This service will be subject to Black Hills Energy tariffs filed with the Colorado Public Utilities Commission and the Black Hills Energy Gas Network Main Extension Policy. If you have any questions please feel free to contact me. Sincerely, Jason Cox Utility Construction Planner Black Hills Energy Jason.cox@blackhillscorp.com Cell: 970-309-2432 Jason Cox Utility Construction Planner Colorado Gas Jason.cox@blackhillscorp.com Comcast. July 11, 2018 Sopris Engineering Attn: Jesse Swann Aspen, Colorado 81611 RE: Gorsuch Haus Aspen, Colorado Please accept this letter as confirmation that Comcast of Colorado/Florida, Inc. has the ability to provide cable service to the captioned location. The provision of service is contingent upon successful negotiations of an Agreement between the developer and Comcast Cable Communications, Inc. Should you require additional information, please contact Michael Johnson. I can be reached at (970) 930-4713 or by email at MichaelJohnson@cable.comcast.com Sincerely, C'LA LL Michael Johnsorl Construction/Engineering Comcast Cable Communications This letter is not intended to give rise to binding obligations for either party. Any contractual relationship between the parties will be the result of formal negotiations and will only become effective upon execution of the contract by representatives of the parties authorized to enter into such agreements. During any negotiations, each party will bear its own costs and will not be responsible for any costs or expenses of the other party, unless separately agreed to in writing. 08/23/2018 Attn: Jesse K. Swann, P.E. Sopris Engineering, LLC CARBONDALE, CO 81623 (970) 704-0311 ext. 43 FAX: (970)-704-0313 RE: Gorsuch Haus To whom it may concern: Your request for facilities to the Gorsuch Haus is within CenturyLink’s serving area and will be provided in accordance with all the rates and tariffs set forth by the Colorado Public Utilities Commission. Connections to CenturyLink facilities are contingent upon the customer meeting all the requirements of the Utilities tariffs that are in effect for each requested utility service at the time the application for service is made by the customer and formally accepted by CenturyLink. Connection requirements may include provisions for necessary line extensions and/or other system improvements, and payment of all applicable system development charges, recovery agreement charges and other fees or charges applicable to the requested service. Although CenturyLink diligently seeks to expand its facilities as necessary to meet anticipated growth, CenturyLink services are provided to eligible customers at the time of connection to the facilities on a “first come, first served” basis after acceptance of the customer’s application as described above. In certain instances, our facilities and capacities may be limited. Accordingly, no specific allocations or amounts of CenturyLink facilities or supplies are reserved for service to the subject property, and no commitments are made as to the availability of CenturyLink service at future times. Sincerely, Jason Sharpe Senior Field Engineer 970-328-8290 Aspen Consolidated Sanitation District John Keleher - President Stoney Davis - Member Joe Zanin - Vice President Jeff Yusem - Member Roy Holloway - Secretary/Treasurer July 10, 2018 Jesse Swann Sopris Engineering 502 Main St. Suite A-3 Carbondale, CO 81623 RE: Gorsuch Haus - Commitment for Sanitary Sewer Service Dear Jesse, Bruce Matherly - Manager The Aspen Consolidated Sanitation District currently has sufficient wastewater collection and treatment capacity to serve this project. Service is contingent upon compliance with the district's rules, regulations, and specifications, which are on file at the District office. There are downstream constraints in the District's collection system that will be corrected through a system of proportionate impact fees. A tap permit must be completed at our office when detailed plans become available. Fees will be estimated at that time. The total connection charges due the District must be paid prior to the issuance of a foundation and/or infrastructure permit. Existing service lines or laterals connected to the District's main line, serving the subject property and adjacent properties must be identified, located and isolated from soil stabilization processes or other potential damage, or, properly disconnected from the ACSD main line at the point of connection according to specific ACSD requirements. Once detailed plans are made available to the district, we can comment specifically about this proposed project. Sincer , H5 ilton T arp Collection Systems Superintendent CC Bruce Matherly, ACSD District Manager 565 North Mill Street Aspen, Colorado 81611 970.925.3601 FAX 970.925.2537 3799 HIGHWAY 82∙P.O. BOX 2150 GLENWOOD SPRINGS, COLORADO 81602 (970) 945-5491∙FAX (970) 945-4081 A Touchstone Energy Cooperative December 12, 2019 Jesse Swann Sopris Engineering 502 Main Street, Suite A3 Carbondale, CO 81623 RE: Gorsuch Haus To Whom it May Concern, The above mentioned development is within the certified service area of Holy Cross Energy. Holy Cross Energy has adequate power supply to provide electric power to the development, subject to tariffs, rules and regulations on file. Any power line enlargements, relocations, and new extensions necessary to deliver adequate power to and within the development will be undertaken by Holy Cross Energy upon completion of appropriate contractual agreements and subject to necessary governmental approvals. Please advise when you wish to proceed with the development of the electric system for this project. Sincerely, HOLY CROSS ENERGY Libby Cowling, Engineering Department lcowling@holycross.com (970) 947-5428 LC:MM WO#23722: Gorsuch Haus;90-68 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Project Description 15101.06-Onsite-DEV-10YR-RATIONAL.SPF Project Options CFS Elevation Rational SCS TR-55 Hydrodynamic YES YES Rainfall Details 10 year(s)Return Period........................................................................ Elevation Type ...................................................................... Hydrology Method ................................................................. Time of Concentration (TOC) Method .................................. Link Routing Method ............................................................. Enable Overflow Ponding at Nodes ...................................... Skip Steady State Analysis Time Periods ............................ File Name ............................................................................. Description ............................................................................ Gorsuch Haus Lodge Draiange - 10 YR Flow Units ............................................................................. Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin Summary SN Subbasin Area Weighted Total Total Total Peak Time of ID Runoff Rainfall Runoff Runoff Runoff Concentration Coefficient Volume (ft²)(in)(in)(ac-in)(cfs)(days hh:mm:ss) 1 0S-5 32234.01 0.7800 0.31 0.24 0.18 2.15 0 00:05:00 2 DE-01 22875.01 0.8700 0.31 0.27 0.14 1.70 0 00:05:00 3 DE-02 16509.98 0.8700 0.31 0.27 0.10 1.23 0 00:05:00 4 EX-04 5500463.51 0.1500 0.71 0.11 13.38 20.95 0 00:38:22 5 POST OS1 984447.98 0.1500 0.67 0.10 2.26 4.67 0 00:29:12 6 POST OS3.1 17439.25 0.2600 0.45 0.12 0.05 0.28 0 00:10:00 7 POST OS3.2 19814.01 0.2500 0.45 0.11 0.05 0.31 0 00:10:00 8 POST OS3.3 38388.77 0.1500 0.50 0.07 0.07 0.33 0 00:11:45 9 POST OS3.4 70916.99 0.1700 0.53 0.09 0.14 0.65 0 00:13:15 10 POST S Aspen St 12181.99 0.6800 0.31 0.21 0.06 0.71 0 00:05:00 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Node Summary SN Element Element Invert Ground/Rim Initial Surcharge Ponded Peak Max HGL ID Type Elevation (Max)Water Elevation Area Inflow Elevation Elevation Elevation Attained (ft)(ft)(ft)(ft)(ft²)(cfs)(ft) 1 DIV-PIONEER Junction 8045.00 8047.00 8045.00 8047.00 0.00 20.95 8045.22 2 EX MH Junction 7995.00 8000.20 7995.00 8000.20 0.00 4.59 7995.48 3 J2 Junction 7994.00 7998.00 7994.00 7998.00 0.00 1.67 7994.22 4 J3 Junction 7995.00 7998.00 7995.00 7998.00 0.00 1.21 7995.24 5 J4-DE 2 Junction 8029.00 8033.00 8029.00 8033.00 0.00 1.23 8029.27 6 J-C0A INLET1 Junction 7977.60 7989.30 7977.60 7989.30 0.00 4.59 7978.13 7 J-C0A INLET2 Junction 7984.65 7994.74 7984.65 7994.74 0.00 4.59 7985.23 8 J-COA INLET4 Junction 7979.30 7988.39 7979.30 7988.39 0.00 4.36 7980.16 9 J-DE01 Junction 8015.00 8019.00 8015.00 8019.00 0.00 1.70 8015.36 10 J-MH-A Junction 7982.50 7996.80 7982.50 7996.80 0.00 3.74 7983.44 11 J-MH-B Junction 7985.35 7997.83 7985.35 7997.83 0.00 3.74 7986.43 12 J-MH-C Junction 7986.50 7997.40 7986.50 7997.40 0.00 2.43 7987.48 13 J-MH-D Junction 7990.80 7996.00 7990.80 7998.00 133.00 2.43 7991.11 14 Jun-24 Junction 8009.25 8012.00 8009.25 8012.00 0.00 4.65 8009.83 15 J-WESTSWALE Junction 8062.00 8064.00 8062.00 8064.00 0.00 4.67 8062.27 16 J-SAS-10 Outfall 7965.15 4.36 7965.15 17 J-SAS-11 Outfall 7965.46 4.59 7965.46 18 OUT-EX-04D Outfall 8042.00 18.38 8042.21 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Link Summary SN Element Element From To (Outlet)Length Inlet Outlet Diameter or Manning's Peak Design Flow Peak Flow Peak Flow Peak Flow ID Type (Inlet)Node Invert Invert Height Roughness Flow Capacity Velocity Depth Depth/ Node Elevation Elevation Total Depth Ratio (ft)(ft)(ft)(in)(cfs)(cfs)(ft/sec)(ft) 1 L-C2 Pipe J3 J-MH-C 65.84 7995.00 7987.68 10.000 0.0130 1.20 7.31 9.45 0.24 0.28 2 L-EAST OS STORM Pipe J4-DE 2 J3 209.03 8029.00 7995.00 6.000 0.0130 1.21 2.26 11.98 0.26 0.51 3 L-EX TO SAS-11 Pipe J-C0A INLET1 J-SAS-11 63.00 7977.77 7966.95 18.000 0.0130 4.59 43.53 14.82 0.35 0.23 4 L-EX-TO SAS-10 Pipe J-COA INLET4 J-SAS-10 68.00 7979.80 7968.54 18.000 0.0130 4.36 42.74 14.52 0.34 0.23 5 Link-14 Pipe J2 J-MH-B 14.83 7994.00 7986.72 10.000 0.0130 1.66 15.35 15.91 0.20 0.25 6 Link-16 Pipe J-C0A INLET2 J-C0A INLET1 33.50 7984.85 7978.16 18.000 0.0130 4.59 46.94 14.78 0.35 0.23 7 Link-25 Pipe EX-INLET OS-5 J-C0A INLET2 28.50 7989.96 7984.74 18.000 0.0130 4.59 44.96 11.10 0.43 0.28 8 Link-29 Pipe J-INLET-3 EX MH 37.20 7998.63 7995.29 18.000 0.0130 4.59 31.48 10.98 0.43 0.29 9 Link-30 Pipe EX MH EX-INLET OS-5 45.20 7995.09 7989.77 18.000 0.0130 4.59 36.04 9.69 0.47 0.31 10 L-PIPE-2 Pipe J-MH-A J-COA INLET4 44.00 7983.00 7980.00 18.000 0.0130 3.74 27.43 9.63 0.41 0.27 11 L-PIPE-3 Pipe J-MH-B J-MH-A 83.00 7985.85 7984.20 18.000 0.0130 3.74 14.81 6.41 0.55 0.37 12 L-PIPE-4 Pipe J-MH-C J-MH-B 47.00 7987.00 7986.05 18.000 0.0130 2.43 14.93 5.56 0.44 0.30 13 L-PIPE5 Pipe J-MH-D J-MH-C 34.00 7990.80 7987.20 18.000 0.0130 2.43 34.18 9.95 0.29 0.20 14 L-PIPE6 Pipe J-INLET6 J-MH-D 96.00 8000.00 7991.00 15.000 0.0130 2.43 19.78 10.47 0.30 0.24 15 L-PIPE6A Pipe J-INLET7 J-INLET6 33.00 8003.41 8000.20 12.000 0.0130 2.43 11.11 10.00 0.35 0.35 16 L-PIPE7 Pipe J-INLET8 J-INLET6 153.00 8033.00 7999.50 8.000 0.0130 0.43 5.65 2.00 0.40 0.59 17 L-WEST OS STORM Pipe J-DE01 J2 244.10 8015.00 7994.00 8.000 0.0130 1.67 3.54 11.45 0.29 0.44 18 L-EX04 Channel DIV-PIONEER OUT-EX-04D 40.18 8045.00 8042.00 12.000 0.0320 18.38 238.15 4.33 0.21 0.21 19 L-PIONEER_DIVERSION Channel DIV-PIONEER J-INLET7 342.61 8045.00 8008.00 12.000 0.0320 2.55 24.45 3.40 0.41 0.41 20 L-W SWALE MAX Channel J-WESTSWALE Jun-24 160.00 8062.00 8009.25 18.000 0.0500 4.65 149.16 3.36 0.42 0.28 21 SWALE-03D1 Channel J-INLET6 J-MH-D 108.52 8007.22 7996.00 18.000 0.0350 0.16 95.98 2.01 0.07 0.04 22 SWALE-03D2 Channel J-INLET8 J-INLET6 195.00 8037.00 8007.22 18.000 0.0350 0.22 116.65 2.60 0.07 0.05 23 SWALE-INLET7TO1 Channel J-INLET7 J-MH-D 116.99 8008.00 7996.00 6.000 0.0250 0.00 59.55 0.00 0.00 0.00 24 W SWALE MIN Channel Jun-24 J-INLET-3 78.61 8009.25 8007.20 18.000 0.0500 4.59 41.95 2.57 0.51 0.34 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Inlet Summary SN Element Inlet Manufacturer Number of Catchbasin Max (Rim)Peak Peak Flow Peak Flow Inlet ID Manufacturer Part Inlets Invert Elevation Flow Intercepted Bypassing Efficiency Number Elevation by Inlet during Peak Inlet Flow (ft)(ft)(cfs)(cfs)(cfs)(%) 1 EX-INLET OS-5 NEENAH FOUNDRY R-4894 1 7989.77 7999.78 2.15 N/A N/A N/A 2 J-INLET-3 NEENAH FOUNDRY R-4895-2 1 7998.63 8007.20 0.00 N/A N/A N/A 3 J-INLET6 FHWA HEC-22 GENERIC N/A 1 7999.50 8007.22 0.47 0.31 0.16 65.32 4 J-INLET7 NEENAH FOUNDRY R-4826 1 8003.41 8008.00 2.55 N/A N/A N/A 5 J-INLET8 FHWA HEC-22 GENERIC N/A 1 8032.50 8037.00 0.65 0.43 0.22 66.42 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin Hydrology Subbasin : 0S-5 Input Data Area (ft²) .........................................................................32234.01 Weighted Runoff Coefficient ..........................................0.7800 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. -32234.01 -0.78 Composite Area & Weighted Runoff Coeff.32234.01 0.78 Time of Concentration TOC Method : SCS TR-55 Sheet Flow Equation : Tc = (0.007 * ((n * Lf)^0.8)) / ((P^0.5) * (Sf^0.4)) Where : Tc = Time of Concentration (hr) n = Manning's roughness Lf = Flow Length (ft) P = 2 yr, 24 hr Rainfall (inches) Sf = Slope (ft/ft) Shallow Concentrated Flow Equation : V = 16.1345 * (Sf^0.5) (unpaved surface) V = 20.3282 * (Sf^0.5) (paved surface) V = 15.0 * (Sf^0.5) (grassed waterway surface) V = 10.0 * (Sf^0.5) (nearly bare & untilled surface) V = 9.0 * (Sf^0.5) (cultivated straight rows surface) V = 7.0 * (Sf^0.5) (short grass pasture surface) V = 5.0 * (Sf^0.5) (woodland surface) V = 2.5 * (Sf^0.5) (forest w/heavy litter surface) Tc = (Lf / V) / (3600 sec/hr) Where: Tc = Time of Concentration (hr) Lf = Flow Length (ft) V = Velocity (ft/sec) Sf = Slope (ft/ft) Channel Flow Equation : V = (1.49 * (R^(2/3)) * (Sf^0.5)) / n R = Aq / Wp Tc = (Lf / V) / (3600 sec/hr) Where : Tc = Time of Concentration (hr) Lf = Flow Length (ft) R = Hydraulic Radius (ft) Aq = Flow Area (ft²) Wp = Wetted Perimeter (ft) V = Velocity (ft/sec) Sf = Slope (ft/ft) n = Manning's roughness User-Defined TOC override (minutes): 5 Subbasin Runoff Results Total Rainfall (in) ............................................................0.31 Total Runoff (in) .............................................................0.24 Peak Runoff (cfs) ...........................................................2.15 Rainfall Intensity .............................................................3.720 Weighted Runoff Coefficient ..........................................0.7800 Time of Concentration (days hh:mm:ss) ........................0 00:05:00 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : DE-01 Input Data Area (ft²) .........................................................................22875.01 Weighted Runoff Coefficient ..........................................0.8700 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 99%IMPERV_COA_RATIONAL 22875.01 C 0.87 Composite Area & Weighted Runoff Coeff.22875.01 0.87 Time of Concentration User-Defined TOC override (minutes): 5 Subbasin Runoff Results Total Rainfall (in) ............................................................0.31 Total Runoff (in) .............................................................0.27 Peak Runoff (cfs) ...........................................................1.70 Rainfall Intensity .............................................................3.720 Weighted Runoff Coefficient ..........................................0.8700 Time of Concentration (days hh:mm:ss) ........................0 00:05:00 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : DE-02 Input Data Area (ft²) .........................................................................16509.98 Weighted Runoff Coefficient ..........................................0.8700 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 99%IMPERV_COA_RATIONAL 16509.98 C 0.87 Composite Area & Weighted Runoff Coeff.16509.98 0.87 Time of Concentration User-Defined TOC override (minutes): 5 Subbasin Runoff Results Total Rainfall (in) ............................................................0.31 Total Runoff (in) .............................................................0.27 Peak Runoff (cfs) ...........................................................1.23 Rainfall Intensity .............................................................3.720 Weighted Runoff Coefficient ..........................................0.8700 Time of Concentration (days hh:mm:ss) ........................0 00:05:00 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : EX-04 Input Data Area (ft²) .........................................................................5500463.51 Weighted Runoff Coefficient ..........................................0.1500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 2%IMPERV_COA_C 5500463.51 C 0.15 Composite Area & Weighted Runoff Coeff.5500463.51 0.15 Time of Concentration User-Defined TOC override (minutes): 38.37 Subbasin Runoff Results Total Rainfall (in) ............................................................0.71 Total Runoff (in) .............................................................0.11 Peak Runoff (cfs) ...........................................................20.95 Rainfall Intensity .............................................................1.106 Weighted Runoff Coefficient ..........................................0.1500 Time of Concentration (days hh:mm:ss) ........................0 00:38:22 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST OS1 Input Data Area (ft²) .........................................................................984447.98 Weighted Runoff Coefficient ..........................................0.1500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. From_URMP 982437.17 C 0.15 Composite Area & Weighted Runoff Coeff.982437.17 0.15 Time of Concentration User-Defined TOC override (minutes): 29.2 Subbasin Runoff Results Total Rainfall (in) ............................................................0.67 Total Runoff (in) .............................................................0.10 Peak Runoff (cfs) ...........................................................4.67 Rainfall Intensity .............................................................1.376 Weighted Runoff Coefficient ..........................................0.1500 Time of Concentration (days hh:mm:ss) ........................0 00:29:12 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST OS3.1 Input Data Area (ft²) .........................................................................17439.25 Weighted Runoff Coefficient ..........................................0.2600 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 17%IMPERV_COA_C 17439.25 C 0.26 Composite Area & Weighted Runoff Coeff.17439.25 0.26 Time of Concentration User-Defined TOC override (minutes): 10.00 Subbasin Runoff Results Total Rainfall (in) ............................................................0.45 Total Runoff (in) .............................................................0.12 Peak Runoff (cfs) ...........................................................0.28 Rainfall Intensity .............................................................2.720 Weighted Runoff Coefficient ..........................................0.2600 Time of Concentration (days hh:mm:ss) ........................0 00:10:00 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST OS3.2 Input Data Area (ft²) .........................................................................19814.01 Weighted Runoff Coefficient ..........................................0.2500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 16%IMPERV_COA_C 19814.01 C 0.25 Composite Area & Weighted Runoff Coeff.19814.01 0.25 Time of Concentration User-Defined TOC override (minutes): 10 Subbasin Runoff Results Total Rainfall (in) ............................................................0.45 Total Runoff (in) .............................................................0.11 Peak Runoff (cfs) ...........................................................0.31 Rainfall Intensity .............................................................2.720 Weighted Runoff Coefficient ..........................................0.2500 Time of Concentration (days hh:mm:ss) ........................0 00:10:00 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST OS3.3 Input Data Area (ft²) .........................................................................38388.77 Weighted Runoff Coefficient ..........................................0.1500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 2%IMPERV_COA_C 38388.77 C 0.15 Composite Area & Weighted Runoff Coeff.38388.77 0.15 Time of Concentration User-Defined TOC override (minutes): 11.76 Subbasin Runoff Results Total Rainfall (in) ............................................................0.50 Total Runoff (in) .............................................................0.07 Peak Runoff (cfs) ...........................................................0.33 Rainfall Intensity .............................................................2.508 Weighted Runoff Coefficient ..........................................0.1500 Time of Concentration (days hh:mm:ss) ........................0 00:11:46 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST OS3.4 Input Data Area (ft²) .........................................................................70916.99 Weighted Runoff Coefficient ..........................................0.1700 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 5%IMPERV_COA_C 70916.99 C 0.17 Composite Area & Weighted Runoff Coeff.70916.99 0.17 Time of Concentration User-Defined TOC override (minutes): 13.26 Subbasin Runoff Results Total Rainfall (in) ............................................................0.53 Total Runoff (in) .............................................................0.09 Peak Runoff (cfs) ...........................................................0.65 Rainfall Intensity .............................................................2.361 Weighted Runoff Coefficient ..........................................0.1700 Time of Concentration (days hh:mm:ss) ........................0 00:13:16 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST S Aspen St Input Data Area (ft²) .........................................................................12181.99 Weighted Runoff Coefficient ..........................................0.6800 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 71%IMPERV_COA_RATIONAL 12181.99 C 0.68 Composite Area & Weighted Runoff Coeff.12181.99 0.68 Time of Concentration User-Defined TOC override (minutes): 5.00 Subbasin Runoff Results Total Rainfall (in) ............................................................0.31 Total Runoff (in) .............................................................0.21 Peak Runoff (cfs) ...........................................................0.71 Rainfall Intensity .............................................................3.720 Weighted Runoff Coefficient ..........................................0.6800 Time of Concentration (days hh:mm:ss) ........................0 00:05:00 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Junction Input SN Element Invert Ground/Rim Ground/Rim ID Elevation (Max)(Max) Elevation Offset (ft)(ft)(ft) 1 DIV-PIONEER 8045.00 8047.00 2.00 2 EX MH 7995.00 8000.20 5.20 3 J2 7994.00 7998.00 4.00 4 J3 7995.00 7998.00 3.00 5 J4-DE 2 8029.00 8033.00 4.00 6 J-C0A INLET1 7977.60 7989.30 11.70 7 J-C0A INLET2 7984.65 7994.74 10.09 8 J-COA INLET4 7979.30 7988.39 9.09 9 J-DE01 8015.00 8019.00 4.00 10 J-MH-A 7982.50 7996.80 14.30 11 J-MH-B 7985.35 7997.83 12.48 12 J-MH-C 7986.50 7997.40 10.90 13 J-MH-D 7990.80 7996.00 5.20 14 Jun-24 8009.25 8012.00 2.75 15 J-WESTSWALE 8062.00 8064.00 2.00 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Junction Results SN Element Peak Peak Max HGL Max HGL Min Average HGL Average HGL Time of Time of ID Inflow Lateral Elevation Depth Freeboard Elevation Depth Max HGL Peak Inflow Attained Attained Attained Attained Attained Occurrence Flooding Occurrence (cfs)(cfs)(ft)(ft)(ft)(ft)(ft)(days hh:mm)(days hh:mm) 1 DIV-PIONEER 20.95 20.95 8045.22 0.22 1.78 8045.11 0.11 0 00:38 0 00:00 2 EX MH 4.59 0.00 7995.48 0.48 4.72 7995.25 0.25 0 00:30 0 00:00 3 J2 1.67 0.00 7994.22 0.22 3.78 7994.02 0.02 0 00:05 0 00:00 4 J3 1.21 0.00 7995.24 0.24 2.76 7995.03 0.03 0 00:05 0 00:00 5 J4-DE 2 1.23 1.23 8029.27 0.27 3.73 8029.03 0.03 0 00:05 0 00:00 6 J-C0A INLET1 4.59 0.00 7978.13 0.53 11.17 7977.94 0.34 0 00:30 0 00:00 7 J-C0A INLET2 4.59 0.00 7985.23 0.58 9.51 7985.02 0.37 0 00:30 0 00:00 8 J-COA INLET4 4.36 0.71 7980.16 0.86 8.23 7979.98 0.68 0 00:06 0 00:00 9 J-DE01 1.70 1.70 8015.36 0.36 3.64 8015.04 0.04 0 00:05 0 00:00 10 J-MH-A 3.74 0.00 7983.44 0.94 13.36 7983.22 0.72 0 00:06 0 00:00 11 J-MH-B 3.74 0.00 7986.43 1.08 11.40 7986.15 0.80 0 00:06 0 00:00 12 J-MH-C 2.43 0.00 7987.48 0.98 9.92 7987.30 0.80 0 00:42 0 00:00 13 J-MH-D 2.43 0.28 7991.11 0.31 6.39 7990.99 0.19 0 00:41 0 00:00 14 Jun-24 4.65 0.00 8009.83 0.58 2.17 8009.50 0.25 0 00:30 0 00:00 15 J-WESTSWALE 4.67 4.67 8062.27 0.27 1.73 8062.11 0.11 0 00:29 0 00:00 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Channel Input SN Element Length Inlet Inlet Outlet Outlet Total Average Shape Height Width Manning's ID Invert Invert Invert Invert Drop Slope Roughness Elevation Offset Elevation Offset (ft)(ft)(ft)(ft)(ft)(ft)(%)(ft)(ft) 1 L-EX04 40.18 8045.00 0.00 8042.00 0.00 3.00 7.4700 Rectangular 1.000 20.000 0.0320 2 L-PIONEER_DIVERSION 342.61 8045.00 0.00 8008.00 4.59 37.00 10.8000 Rectangular 1.000 2.400 0.0320 3 L-W SWALE MAX 160.00 8062.00 0.00 8009.25 0.00 52.75 32.9700 Trapezoidal 1.500 11.000 0.0500 4 SWALE-03D1 108.52 8007.22 7.72 7996.00 5.20 11.22 10.3400 Trapezoidal 1.500 10.000 0.0350 5 SWALE-03D2 195.00 8037.00 4.50 8007.22 7.72 29.78 15.2700 Trapezoidal 1.500 10.000 0.0350 6 SWALE-INLET7TO1 116.99 8008.00 4.59 7996.00 5.20 12.00 10.2600 Trapezoidal 0.500 11.000 0.0250 7 W SWALE MIN 78.61 8009.25 0.00 8007.20 8.57 2.05 2.6100 Trapezoidal 1.500 11.000 0.0500 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Channel Results SN Element Peak Time of Design Flow Peak Flow/Peak Flow Travel Peak Flow Peak Flow ID Flow Peak Flow Capacity Design Flow Velocity Time Depth Depth/ Occurrence Ratio Total Depth Ratio (cfs)(days hh:mm)(cfs)(ft/sec)(min)(ft) 1 L-EX04 18.38 0 00:38 238.15 0.08 4.33 0.15 0.21 0.21 2 L-PIONEER_DIVERSION 2.55 0 00:38 24.45 0.10 3.40 1.68 0.41 0.41 3 L-W SWALE MAX 4.65 0 00:29 149.16 0.03 3.36 0.79 0.42 0.28 4 SWALE-03D1 0.16 0 00:11 95.98 0.00 2.01 0.90 0.07 0.04 5 SWALE-03D2 0.22 0 00:13 116.65 0.00 2.60 1.25 0.07 0.05 6 SWALE-INLET7TO1 0.00 0 00:00 59.55 0.00 0.00 0.00 0.00 7 W SWALE MIN 4.59 0 00:30 41.95 0.11 2.57 0.51 0.51 0.34 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Pipe Input SN Element Length Inlet Inlet Outlet Outlet Total Average Pipe Pipe Pipe ID Invert Invert Invert Invert Drop Slope Shape Diameter or Width Elevation Offset Elevation Offset Height (ft)(ft)(ft)(ft)(ft)(ft)(%)(in)(in) 1 L-C2 65.84 7995.00 0.00 7987.68 1.18 7.32 11.1200 CIRCULAR 9.960 9.960 2 L-EAST OS STORM 209.03 8029.00 0.00 7995.00 0.00 34.00 16.2700 CIRCULAR 6.000 6.000 3 L-EX TO SAS-11 63.00 7977.77 0.17 7966.95 1.49 10.82 17.1700 CIRCULAR 18.000 18.000 4 L-EX-TO SAS-10 68.00 7979.80 0.50 7968.54 3.39 11.26 16.5600 CIRCULAR 18.000 18.000 5 Link-14 14.83 7994.00 0.00 7986.72 1.37 7.28 49.0900 CIRCULAR 9.960 9.960 6 Link-16 33.50 7984.85 0.20 7978.16 0.56 6.69 19.9700 CIRCULAR 18.000 18.000 7 Link-25 28.50 7989.96 0.19 7984.74 0.09 5.22 18.3200 CIRCULAR 18.000 18.000 8 Link-29 37.20 7998.63 0.00 7995.29 0.29 3.34 8.9800 CIRCULAR 18.000 18.000 9 Link-30 45.20 7995.09 0.09 7989.77 0.00 5.32 11.7700 CIRCULAR 18.000 18.000 10 L-PIPE-2 44.00 7983.00 0.50 7980.00 0.70 3.00 6.8200 CIRCULAR 18.000 18.000 11 L-PIPE-3 83.00 7985.85 0.50 7984.20 1.70 1.65 1.9900 CIRCULAR 18.000 18.000 12 L-PIPE-4 47.00 7987.00 0.50 7986.05 0.70 0.95 2.0200 CIRCULAR 18.000 18.000 13 L-PIPE5 34.00 7990.80 0.00 7987.20 0.70 3.60 10.5900 CIRCULAR 18.000 18.000 14 L-PIPE6 96.00 8000.00 0.50 7991.00 0.20 9.00 9.3800 CIRCULAR 15.000 15.000 15 L-PIPE6A 33.00 8003.41 0.00 8000.20 0.70 3.21 9.7300 CIRCULAR 12.000 12.000 16 L-PIPE7 153.00 8033.00 0.50 7999.50 0.00 33.50 21.9000 CIRCULAR 8.040 8.040 17 L-WEST OS STORM 244.10 8015.00 0.00 7994.00 0.00 21.00 8.6000 CIRCULAR 8.040 8.040 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Pipe Results SN Element Peak Time of Design Flow Peak Flow/Peak Flow Travel Peak Flow Peak Flow ID Flow Peak Flow Capacity Design Flow Velocity Time Depth Depth/ Occurrence Ratio Total Depth Ratio (cfs)(days hh:mm)(cfs)(ft/sec)(min)(ft) 1 L-C2 1.20 0 00:05 7.31 0.16 9.45 0.12 0.24 0.28 2 L-EAST OS STORM 1.21 0 00:05 2.26 0.53 11.98 0.29 0.26 0.51 3 L-EX TO SAS-11 4.59 0 00:30 43.53 0.11 14.82 0.07 0.35 0.23 4 L-EX-TO SAS-10 4.36 0 00:06 42.74 0.10 14.52 0.08 0.34 0.23 5 Link-14 1.66 0 00:05 15.35 0.11 15.91 0.02 0.20 0.25 6 Link-16 4.59 0 00:30 46.94 0.10 14.78 0.04 0.35 0.23 7 Link-25 4.59 0 00:30 44.96 0.10 11.10 0.04 0.43 0.28 8 Link-29 4.59 0 00:30 31.48 0.15 10.98 0.06 0.43 0.29 9 Link-30 4.59 0 00:30 36.04 0.13 9.69 0.08 0.47 0.31 10 L-PIPE-2 3.74 0 00:06 27.43 0.14 9.63 0.08 0.41 0.27 11 L-PIPE-3 3.74 0 00:06 14.81 0.25 6.41 0.22 0.55 0.37 12 L-PIPE-4 2.43 0 00:42 14.93 0.16 5.56 0.14 0.44 0.30 13 L-PIPE5 2.43 0 00:41 34.18 0.07 9.95 0.06 0.29 0.20 14 L-PIPE6 2.43 0 00:41 19.78 0.12 10.47 0.15 0.30 0.24 15 L-PIPE6A 2.43 0 00:41 11.11 0.22 10.00 0.06 0.35 0.35 16 L-PIPE7 0.43 0 00:13 5.65 0.08 2.00 1.28 0.40 0.59 17 L-WEST OS STORM 1.67 0 00:05 3.54 0.47 11.45 0.36 0.29 0.44 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Inlet Input SN Element Inlet Manufacturer Number of Catchbasin Max (Rim)Inlet Initial Initial Grate ID Manufacturer Part Inlets Invert Elevation Depth Water Water Clogging Number Elevation Elevation Depth Factor (ft)(ft)(ft)(ft)(ft)(%) 1 EX-INLET OS-5 NEENAH FOUNDRY R-4894 1 7989.77 7999.78 10.01 7989.77 0.00 50.00 2 J-INLET-3 NEENAH FOUNDRY R-4895-2 1 7998.63 8007.20 8.57 7998.63 0.00 50.00 3 J-INLET6 FHWA HEC-22 GENERIC N/A 1 7999.50 8007.22 7.72 7999.50 0.00 50.00 4 J-INLET7 NEENAH FOUNDRY R-4826 1 8003.41 8008.00 4.59 8003.41 0.00 50.00 5 J-INLET8 FHWA HEC-22 GENERIC N/A 1 8032.50 8037.00 4.50 8032.50 0.00 50.00 Gorsuch Haus Lodge 10-Year Conceptual Drainage Design SE Project #:15101.06 Inlet Results SN Element Peak Peak Peak Flow Peak Flow Inlet ID Flow Lateral Intercepted Bypassing Efficiency Inflow by Inlet during Peak Inlet Flow (cfs)(cfs)(cfs)(cfs)(%) 1 EX-INLET OS-5 2.15 2.15 N/A N/A N/A 2 J-INLET-3 0.00 0.00 N/A N/A N/A 3 J-INLET6 0.47 0.31 0.31 0.16 65.32 4 J-INLET7 2.55 0.33 N/A N/A N/A 5 J-INLET8 0.65 0.65 0.43 0.22 66.42 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Project Description 15101.06-Onsite-DEV-100YR-RATIONAL.SPF Project Options CFS Elevation Rational SCS TR-55 Hydrodynamic YES YES Rainfall Details 100 year(s) Skip Steady State Analysis Time Periods ............................ Return Period........................................................................ Flow Units ............................................................................. Elevation Type ...................................................................... Hydrology Method ................................................................. Time of Concentration (TOC) Method .................................. Link Routing Method ............................................................. Enable Overflow Ponding at Nodes ...................................... File Name ............................................................................. Description ............................................................................ Gorsuch Haus Lodge 15101.06 100-YR Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin Summary SN Subbasin Area Weighted Total Total Total Peak Time of ID Runoff Rainfall Runoff Runoff Runoff Concentration Coefficient Volume (ft²)(in)(in)(ac-in)(cfs)(days hh:mm:ss) 1 0S-5 32234.01 0.8500 0.53 0.45 0.33 3.98 0 00:05:00 2 DE-01 22875.01 0.8900 0.53 0.47 0.25 2.95 0 00:05:00 3 DE-02 16509.98 0.8900 0.53 0.47 0.18 2.13 0 00:05:00 4 EX-04 5500463.51 0.4900 1.16 0.57 71.60 112.03 0 00:38:22 5 POST OS1 984447.98 0.4900 1.11 0.54 12.29 25.31 0 00:29:12 6 POST OS3.1 17439.25 0.5500 0.77 0.42 0.17 1.02 0 00:10:00 7 POST OS3.2 19814.01 0.5500 0.77 0.42 0.19 1.16 0 00:10:00 8 POST OS3.3 38388.77 0.4900 0.84 0.41 0.36 1.84 0 00:11:45 9 POST OS3.4 70916.99 0.5000 0.89 0.45 0.72 3.26 0 00:13:15 10 POST S Aspen St 12181.99 0.7900 0.53 0.42 0.12 1.40 0 00:05:00 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Node Summary SN Element Element Invert Ground/Rim Initial Surcharge Ponded Peak Max HGL ID Type Elevation (Max)Water Elevation Area Inflow Elevation Elevation Elevation Attained (ft)(ft)(ft)(ft)(ft²)(cfs)(ft) 1 DIV-PIONEER Junction 8045.00 8047.00 8045.00 8047.00 0.00 112.03 8045.66 2 EX MH Junction 7995.00 8000.20 7995.00 8000.20 0.00 25.11 7996.95 3 J2 Junction 7994.00 7998.00 7994.00 7998.00 0.00 2.89 7994.32 4 J3 Junction 7995.00 7998.00 7995.00 7998.00 0.00 2.09 7995.33 5 J4-DE 2 Junction 8029.00 8033.00 8029.00 8033.00 0.00 2.13 8029.41 6 J-C0A INLET1 Junction 7977.60 7989.30 7977.60 7989.30 0.00 24.99 7978.88 7 J-C0A INLET2 Junction 7984.65 7994.74 7984.65 7994.74 0.00 24.99 7986.15 8 J-COA INLET4 Junction 7979.30 7988.39 7979.30 7988.39 0.00 11.30 7980.42 9 J-DE01 Junction 8015.00 8019.00 8015.00 8019.00 0.00 2.95 8015.53 10 J-MH-A Junction 7982.50 7996.80 7982.50 7996.80 0.00 11.30 7983.91 11 J-MH-B Junction 7985.35 7997.83 7985.35 7997.83 0.00 11.30 7987.11 12 J-MH-C Junction 7986.50 7997.40 7986.50 7997.40 0.00 11.31 7988.40 13 J-MH-D Junction 7990.80 7996.00 7990.80 7998.00 133.00 11.31 7991.55 14 Jun-24 Junction 8009.25 8012.00 8009.25 8012.00 0.00 25.26 8010.51 15 J-WESTSWALE Junction 8062.00 8064.00 8062.00 8064.00 0.00 25.31 8062.66 16 J-SAS-10 Outfall 7965.15 11.30 7965.15 17 J-SAS-11 Outfall 7965.46 24.99 7965.46 18 OUT-EX-04D Outfall 8042.00 98.96 8042.58 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Link Summary SN Element Element From To (Outlet)Length Inlet Outlet Diameter or Manning's Peak Design Flow Peak Flow Peak Flow Peak Flow ID Type (Inlet)Node Invert Invert Height Roughness Flow Capacity Velocity Depth Depth/ Node Elevation Elevation Total Depth Ratio (ft)(ft)(ft)(in)(cfs)(cfs)(ft/sec)(ft) 1 L-C2 Pipe J3 J-MH-C 65.84 7995.00 7987.68 10.000 0.0130 2.08 7.31 10.86 0.36 0.43 2 L-EAST OS STORM Pipe J4-DE 2 J3 209.03 8029.00 7995.00 6.000 0.0130 2.09 2.26 13.33 0.37 0.74 3 L-EX TO SAS-11 Pipe J-C0A INLET1 J-SAS-11 63.00 7977.77 7966.95 18.000 0.0130 24.99 43.53 20.85 0.96 0.64 4 L-EX-TO SAS-10 Pipe J-COA INLET4 J-SAS-10 68.00 7979.80 7968.54 18.000 0.0130 11.30 42.74 18.13 0.57 0.38 5 Link-14 Pipe J2 J-MH-B 14.83 7994.00 7986.72 10.000 0.0130 2.88 15.35 17.71 0.28 0.34 6 Link-16 Pipe J-C0A INLET2 J-C0A INLET1 33.50 7984.85 7978.16 18.000 0.0130 24.99 46.94 19.26 1.04 0.69 7 Link-25 Pipe EX-INLET OS-5 J-C0A INLET2 28.50 7989.96 7984.74 18.000 0.0130 24.99 44.96 14.97 1.34 0.90 8 Link-29 Pipe J-INLET-3 EX MH 37.20 7998.63 7995.29 18.000 0.0130 25.11 31.48 14.71 1.50 1.00 9 Link-30 Pipe EX MH EX-INLET OS-5 45.20 7995.09 7989.77 18.000 0.0130 24.99 36.04 14.24 1.48 0.99 10 L-PIPE-2 Pipe J-MH-A J-COA INLET4 44.00 7983.00 7980.00 18.000 0.0130 11.30 27.43 11.97 0.79 0.53 11 L-PIPE-3 Pipe J-MH-B J-MH-A 83.00 7985.85 7984.20 18.000 0.0130 11.30 14.81 7.97 1.12 0.75 12 L-PIPE-4 Pipe J-MH-C J-MH-B 47.00 7987.00 7986.05 18.000 0.0130 11.30 14.93 7.37 1.23 0.82 13 L-PIPE5 Pipe J-MH-D J-MH-C 34.00 7990.80 7987.20 18.000 0.0130 11.31 34.18 9.87 0.98 0.65 14 L-PIPE6 Pipe J-INLET6 J-MH-D 96.00 8000.00 7991.00 15.000 0.0130 11.30 19.78 14.98 0.74 0.59 15 L-PIPE6A Pipe J-INLET7 J-INLET6 33.00 8003.41 8000.20 12.000 0.0130 11.30 11.11 14.81 1.00 1.00 16 L-PIPE7 Pipe J-INLET8 J-INLET6 153.00 8033.00 7999.50 8.000 0.0130 1.89 5.65 7.25 0.47 0.70 17 L-WEST OS STORM Pipe J-DE01 J2 244.10 8015.00 7994.00 8.000 0.0130 2.89 3.54 12.42 0.42 0.63 18 L-EX04 Channel DIV-PIONEER OUT-EX-04D 40.18 8045.00 8042.00 12.000 0.0320 98.96 238.15 7.99 0.62 0.62 19 L-PIONEER_DIVERSION Channel DIV-PIONEER J-INLET7 342.61 8045.00 8008.00 12.000 0.0320 13.02 24.45 6.55 0.83 0.83 20 L-W SWALE MAX Channel J-WESTSWALE Jun-24 160.00 8062.00 8009.25 18.000 0.0500 25.26 149.16 5.42 0.96 0.64 21 SWALE-03D1 Channel J-INLET6 J-MH-D 108.52 8007.22 7996.00 18.000 0.0350 0.81 95.98 3.31 0.16 0.11 22 SWALE-03D2 Channel J-INLET8 J-INLET6 195.00 8037.00 8007.22 18.000 0.0350 1.36 116.65 4.81 0.18 0.12 23 SWALE-INLET7TO1 Channel J-INLET7 J-MH-D 116.99 8008.00 7996.00 6.000 0.0250 0.00 59.55 0.00 0.00 0.00 24 W SWALE MIN Channel Jun-24 J-INLET-3 78.61 8009.25 8007.20 18.000 0.0500 25.05 41.95 3.95 1.16 0.77 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Inlet Summary SN Element Inlet Manufacturer Number of Catchbasin Max (Rim)Peak Peak Flow Peak Flow Inlet ID Manufacturer Part Inlets Invert Elevation Flow Intercepted Bypassing Efficiency Number Elevation by Inlet during Peak Inlet Flow (ft)(ft)(cfs)(cfs)(cfs)(%) 1 EX-INLET OS-5 NEENAH FOUNDRY R-4894 1 7989.77 7999.78 3.97 N/A N/A N/A 2 J-INLET-3 NEENAH FOUNDRY R-4895-2 1 7998.63 8007.20 0.00 N/A N/A N/A 3 J-INLET6 FHWA HEC-22 GENERIC N/A 1 7999.50 8007.22 2.27 1.37 0.91 60.15 4 J-INLET7 NEENAH FOUNDRY R-4826 1 8003.41 8008.00 13.02 N/A N/A N/A 5 J-INLET8 FHWA HEC-22 GENERIC N/A 1 8032.50 8037.00 3.26 1.89 1.37 58.02 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin Hydrology Subbasin : 0S-5 Input Data Area (ft²) .........................................................................32234.01 Weighted Runoff Coefficient ..........................................0.8500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. -32234.01 -0.85 Composite Area & Weighted Runoff Coeff.32234.01 0.85 Time of Concentration TOC Method : SCS TR-55 Sheet Flow Equation : Tc = (0.007 * ((n * Lf)^0.8)) / ((P^0.5) * (Sf^0.4)) Where : Tc = Time of Concentration (hr) n = Manning's roughness Lf = Flow Length (ft) P = 2 yr, 24 hr Rainfall (inches) Sf = Slope (ft/ft) Shallow Concentrated Flow Equation : V = 16.1345 * (Sf^0.5) (unpaved surface) V = 20.3282 * (Sf^0.5) (paved surface) V = 15.0 * (Sf^0.5) (grassed waterway surface) V = 10.0 * (Sf^0.5) (nearly bare & untilled surface) V = 9.0 * (Sf^0.5) (cultivated straight rows surface) V = 7.0 * (Sf^0.5) (short grass pasture surface) V = 5.0 * (Sf^0.5) (woodland surface) V = 2.5 * (Sf^0.5) (forest w/heavy litter surface) Tc = (Lf / V) / (3600 sec/hr) Where: Tc = Time of Concentration (hr) Lf = Flow Length (ft) V = Velocity (ft/sec) Sf = Slope (ft/ft) Channel Flow Equation : V = (1.49 * (R^(2/3)) * (Sf^0.5)) / n R = Aq / Wp Tc = (Lf / V) / (3600 sec/hr) Where : Tc = Time of Concentration (hr) Lf = Flow Length (ft) R = Hydraulic Radius (ft) Aq = Flow Area (ft²) Wp = Wetted Perimeter (ft) V = Velocity (ft/sec) Sf = Slope (ft/ft) n = Manning's roughness User-Defined TOC override (minutes): 5 Subbasin Runoff Results Total Rainfall (in) ............................................................0.53 Total Runoff (in) .............................................................0.45 Peak Runoff (cfs) ...........................................................3.98 Rainfall Intensity .............................................................6.320 Weighted Runoff Coefficient ..........................................0.8500 Time of Concentration (days hh:mm:ss) ........................0 00:05:00 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : DE-01 Input Data Area (ft²) .........................................................................22875.01 Weighted Runoff Coefficient ..........................................0.8900 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 99%IMPERV_COA_RATIONAL 22875.01 C 0.89 Composite Area & Weighted Runoff Coeff.22875.01 0.89 Time of Concentration User-Defined TOC override (minutes): 5 Subbasin Runoff Results Total Rainfall (in) ............................................................0.53 Total Runoff (in) .............................................................0.47 Peak Runoff (cfs) ...........................................................2.95 Rainfall Intensity .............................................................6.320 Weighted Runoff Coefficient ..........................................0.8900 Time of Concentration (days hh:mm:ss) ........................0 00:05:00 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : DE-02 Input Data Area (ft²) .........................................................................16509.98 Weighted Runoff Coefficient ..........................................0.8900 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 99%IMPERV_COA_RATIONAL 16509.98 C 0.89 Composite Area & Weighted Runoff Coeff.16509.98 0.89 Time of Concentration User-Defined TOC override (minutes): 5 Subbasin Runoff Results Total Rainfall (in) ............................................................0.53 Total Runoff (in) .............................................................0.47 Peak Runoff (cfs) ...........................................................2.13 Rainfall Intensity .............................................................6.320 Weighted Runoff Coefficient ..........................................0.8900 Time of Concentration (days hh:mm:ss) ........................0 00:05:00 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : EX-04 Input Data Area (ft²) .........................................................................5500463.51 Weighted Runoff Coefficient ..........................................0.4900 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 2%IMPERV_COA_C 5500463.51 C 0.49 Composite Area & Weighted Runoff Coeff.5500463.51 0.49 Time of Concentration User-Defined TOC override (minutes): 38.37 Subbasin Runoff Results Total Rainfall (in) ............................................................1.16 Total Runoff (in) .............................................................0.57 Peak Runoff (cfs) ...........................................................112.03 Rainfall Intensity .............................................................1.811 Weighted Runoff Coefficient ..........................................0.4900 Time of Concentration (days hh:mm:ss) ........................0 00:38:22 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST OS1 Input Data Area (ft²) .........................................................................984447.98 Weighted Runoff Coefficient ..........................................0.4900 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. From_URMP 982437.17 C 0.49 Composite Area & Weighted Runoff Coeff.982437.17 0.49 Time of Concentration User-Defined TOC override (minutes): 29.2 Subbasin Runoff Results Total Rainfall (in) ............................................................1.11 Total Runoff (in) .............................................................0.54 Peak Runoff (cfs) ...........................................................25.31 Rainfall Intensity .............................................................2.286 Weighted Runoff Coefficient ..........................................0.4900 Time of Concentration (days hh:mm:ss) ........................0 00:29:12 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST OS3.1 Input Data Area (ft²) .........................................................................17439.25 Weighted Runoff Coefficient ..........................................0.5500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 17%IMPERV_COA_C 17439.25 C 0.55 Composite Area & Weighted Runoff Coeff.17439.25 0.55 Time of Concentration User-Defined TOC override (minutes): 10.00 Subbasin Runoff Results Total Rainfall (in) ............................................................0.77 Total Runoff (in) .............................................................0.42 Peak Runoff (cfs) ...........................................................1.02 Rainfall Intensity .............................................................4.630 Weighted Runoff Coefficient ..........................................0.5500 Time of Concentration (days hh:mm:ss) ........................0 00:10:00 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST OS3.2 Input Data Area (ft²) .........................................................................19814.01 Weighted Runoff Coefficient ..........................................0.5500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 16%IMPERV_COA_C 19813.00 C 0.55 Composite Area & Weighted Runoff Coeff.19813.00 0.55 Time of Concentration User-Defined TOC override (minutes): 10 Subbasin Runoff Results Total Rainfall (in) ............................................................0.77 Total Runoff (in) .............................................................0.42 Peak Runoff (cfs) ...........................................................1.16 Rainfall Intensity .............................................................4.630 Weighted Runoff Coefficient ..........................................0.5500 Time of Concentration (days hh:mm:ss) ........................0 00:10:00 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST OS3.3 Input Data Area (ft²) .........................................................................38388.77 Weighted Runoff Coefficient ..........................................0.4900 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 2%IMPERV_COA_C 38388.77 C 0.49 Composite Area & Weighted Runoff Coeff.38388.77 0.49 Time of Concentration User-Defined TOC override (minutes): 11.76 Subbasin Runoff Results Total Rainfall (in) ............................................................0.84 Total Runoff (in) .............................................................0.41 Peak Runoff (cfs) ...........................................................1.84 Rainfall Intensity .............................................................4.260 Weighted Runoff Coefficient ..........................................0.4900 Time of Concentration (days hh:mm:ss) ........................0 00:11:46 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST OS3.4 Input Data Area (ft²) .........................................................................70916.99 Weighted Runoff Coefficient ..........................................0.5000 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 5%IMPERV_COA_C 70916.99 C 0.50 Composite Area & Weighted Runoff Coeff.70916.99 0.50 Time of Concentration User-Defined TOC override (minutes): 13.26 Subbasin Runoff Results Total Rainfall (in) ............................................................0.89 Total Runoff (in) .............................................................0.45 Peak Runoff (cfs) ...........................................................3.26 Rainfall Intensity .............................................................4.006 Weighted Runoff Coefficient ..........................................0.5000 Time of Concentration (days hh:mm:ss) ........................0 00:13:16 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Subbasin : POST S Aspen St Input Data Area (ft²) .........................................................................12181.99 Weighted Runoff Coefficient ..........................................0.7900 Runoff Coefficient Area Soil Runoff Soil/Surface Description (ft²)Group Coeff. 71%IMPERV_COA_RATIONAL 12181.99 C 0.79 Composite Area & Weighted Runoff Coeff.12181.99 0.79 Time of Concentration User-Defined TOC override (minutes): 5.00 Subbasin Runoff Results Total Rainfall (in) ............................................................0.53 Total Runoff (in) .............................................................0.42 Peak Runoff (cfs) ...........................................................1.40 Rainfall Intensity .............................................................6.320 Weighted Runoff Coefficient ..........................................0.7900 Time of Concentration (days hh:mm:ss) ........................0 00:05:00 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Junction Input SN Element Invert Ground/Rim Ground/Rim ID Elevation (Max)(Max) Elevation Offset (ft)(ft)(ft) 1 DIV-PIONEER 8045.00 8047.00 2.00 2 EX MH 7995.00 8000.20 5.20 3 J2 7994.00 7998.00 4.00 4 J3 7995.00 7998.00 3.00 5 J4-DE 2 8029.00 8033.00 4.00 6 J-C0A INLET1 7977.60 7989.30 11.70 7 J-C0A INLET2 7984.65 7994.74 10.09 8 J-COA INLET4 7979.30 7988.39 9.09 9 J-DE01 8015.00 8019.00 4.00 10 J-MH-A 7982.50 7996.80 14.30 11 J-MH-B 7985.35 7997.83 12.48 12 J-MH-C 7986.50 7997.40 10.90 13 J-MH-D 7990.80 7996.00 5.20 14 Jun-24 8009.25 8012.00 2.75 15 J-WESTSWALE 8062.00 8064.00 2.00 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Junction Results SN Element Peak Peak Max HGL Max HGL Min Average HGL Average HGL Time of Time of ID Inflow Lateral Elevation Depth Freeboard Elevation Depth Max HGL Peak Inflow Attained Attained Attained Attained Attained Occurrence Flooding Occurrence (cfs)(cfs)(ft)(ft)(ft)(ft)(ft)(days hh:mm)(days hh:mm) 1 DIV-PIONEER 112.03 112.03 8045.66 0.66 1.34 8045.32 0.32 0 00:38 0 00:00 2 EX MH 25.11 0.00 7996.95 1.95 3.25 7995.57 0.57 0 00:29 0 00:00 3 J2 2.89 0.00 7994.32 0.32 3.68 7994.03 0.03 0 00:05 0 00:00 4 J3 2.09 0.00 7995.33 0.33 2.67 7995.03 0.03 0 00:05 0 00:00 5 J4-DE 2 2.13 2.13 8029.41 0.41 3.59 8029.04 0.04 0 00:05 0 00:00 6 J-C0A INLET1 24.99 0.00 7978.88 1.28 10.42 7978.20 0.60 0 00:30 0 00:00 7 J-C0A INLET2 24.99 0.00 7986.15 1.50 8.59 7985.33 0.68 0 00:30 0 00:00 8 J-COA INLET4 11.30 1.40 7980.42 1.12 7.97 7980.23 0.93 0 00:48 0 00:00 9 J-DE01 2.95 2.95 8015.53 0.53 3.47 8015.05 0.05 0 00:05 0 00:00 10 J-MH-A 11.30 0.00 7983.91 1.41 12.89 7983.60 1.10 0 00:48 0 00:00 11 J-MH-B 11.30 0.00 7987.11 1.76 10.72 7986.66 1.31 0 00:48 0 00:00 12 J-MH-C 11.31 0.00 7988.40 1.90 9.00 7987.85 1.35 0 00:47 0 00:00 13 J-MH-D 11.31 1.02 7991.55 0.75 5.95 7991.28 0.48 0 00:47 0 00:00 14 Jun-24 25.26 0.00 8010.51 1.26 1.49 8009.81 0.56 0 00:29 0 00:00 15 J-WESTSWALE 25.31 25.31 8062.66 0.66 1.34 8062.28 0.28 0 00:29 0 00:00 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Channel Input SN Element Length Inlet Inlet Outlet Outlet Total Average Shape Height Width Manning's ID Invert Invert Invert Invert Drop Slope Roughness Elevation Offset Elevation Offset (ft)(ft)(ft)(ft)(ft)(ft)(%)(ft)(ft) 1 L-EX04 40.18 8045.00 0.00 8042.00 0.00 3.00 7.4700 Rectangular 1.000 20.000 0.0320 2 L-PIONEER_DIVERSION 342.61 8045.00 0.00 8008.00 4.59 37.00 10.8000 Rectangular 1.000 2.400 0.0320 3 L-W SWALE MAX 160.00 8062.00 0.00 8009.25 0.00 52.75 32.9700 Trapezoidal 1.500 11.000 0.0500 4 SWALE-03D1 108.52 8007.22 7.72 7996.00 5.20 11.22 10.3400 Trapezoidal 1.500 10.000 0.0350 5 SWALE-03D2 195.00 8037.00 4.50 8007.22 7.72 29.78 15.2700 Trapezoidal 1.500 10.000 0.0350 6 SWALE-INLET7TO1 116.99 8008.00 4.59 7996.00 5.20 12.00 10.2600 Trapezoidal 0.500 11.000 0.0250 7 W SWALE MIN 78.61 8009.25 0.00 8007.20 8.57 2.05 2.6100 Trapezoidal 1.500 11.000 0.0500 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Channel Results SN Element Peak Time of Design Flow Peak Flow/Peak Flow Travel Peak Flow Peak Flow ID Flow Peak Flow Capacity Design Flow Velocity Time Depth Depth/ Occurrence Ratio Total Depth Ratio (cfs)(days hh:mm)(cfs)(ft/sec)(min)(ft) 1 L-EX04 98.96 0 00:38 238.15 0.42 7.99 0.08 0.62 0.62 2 L-PIONEER_DIVERSION 13.02 0 00:38 24.45 0.53 6.55 0.87 0.83 0.83 3 L-W SWALE MAX 25.26 0 00:29 149.16 0.17 5.42 0.49 0.96 0.64 4 SWALE-03D1 0.81 0 00:13 95.98 0.01 3.31 0.55 0.16 0.11 5 SWALE-03D2 1.36 0 00:13 116.65 0.01 4.81 0.68 0.18 0.12 6 SWALE-INLET7TO1 0.00 0 00:00 59.55 0.00 0.00 0.00 0.00 7 W SWALE MIN 25.05 0 00:29 41.95 0.60 3.95 0.33 1.16 0.77 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Pipe Input SN Element Length Inlet Inlet Outlet Outlet Total Average Pipe Pipe Pipe ID Invert Invert Invert Invert Drop Slope Shape Diameter or Width Elevation Offset Elevation Offset Height (ft)(ft)(ft)(ft)(ft)(ft)(%)(in)(in) 1 L-C2 65.84 7995.00 0.00 7987.68 1.18 7.32 11.1200 CIRCULAR 9.960 9.960 2 L-EAST OS STORM 209.03 8029.00 0.00 7995.00 0.00 34.00 16.2700 CIRCULAR 6.000 6.000 3 L-EX TO SAS-11 63.00 7977.77 0.17 7966.95 1.49 10.82 17.1700 CIRCULAR 18.000 18.000 4 L-EX-TO SAS-10 68.00 7979.80 0.50 7968.54 3.39 11.26 16.5600 CIRCULAR 18.000 18.000 5 Link-14 14.83 7994.00 0.00 7986.72 1.37 7.28 49.0900 CIRCULAR 9.960 9.960 6 Link-16 33.50 7984.85 0.20 7978.16 0.56 6.69 19.9700 CIRCULAR 18.000 18.000 7 Link-25 28.50 7989.96 0.19 7984.74 0.09 5.22 18.3200 CIRCULAR 18.000 18.000 8 Link-29 37.20 7998.63 0.00 7995.29 0.29 3.34 8.9800 CIRCULAR 18.000 18.000 9 Link-30 45.20 7995.09 0.09 7989.77 0.00 5.32 11.7700 CIRCULAR 18.000 18.000 10 L-PIPE-2 44.00 7983.00 0.50 7980.00 0.70 3.00 6.8200 CIRCULAR 18.000 18.000 11 L-PIPE-3 83.00 7985.85 0.50 7984.20 1.70 1.65 1.9900 CIRCULAR 18.000 18.000 12 L-PIPE-4 47.00 7987.00 0.50 7986.05 0.70 0.95 2.0200 CIRCULAR 18.000 18.000 13 L-PIPE5 34.00 7990.80 0.00 7987.20 0.70 3.60 10.5900 CIRCULAR 18.000 18.000 14 L-PIPE6 96.00 8000.00 0.50 7991.00 0.20 9.00 9.3800 CIRCULAR 15.000 15.000 15 L-PIPE6A 33.00 8003.41 0.00 8000.20 0.70 3.21 9.7300 CIRCULAR 12.000 12.000 16 L-PIPE7 153.00 8033.00 0.50 7999.50 0.00 33.50 21.9000 CIRCULAR 8.040 8.040 17 L-WEST OS STORM 244.10 8015.00 0.00 7994.00 0.00 21.00 8.6000 CIRCULAR 8.040 8.040 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Pipe Results SN Element Peak Time of Design Flow Peak Flow/Peak Flow Travel Peak Flow Peak Flow ID Flow Peak Flow Capacity Design Flow Velocity Time Depth Depth/ Occurrence Ratio Total Depth Ratio (cfs)(days hh:mm)(cfs)(ft/sec)(min)(ft) 1 L-C2 2.08 0 00:05 7.31 0.28 10.86 0.10 0.36 0.43 2 L-EAST OS STORM 2.09 0 00:05 2.26 0.92 13.33 0.26 0.37 0.74 3 L-EX TO SAS-11 24.99 0 00:30 43.53 0.57 20.85 0.05 0.96 0.64 4 L-EX-TO SAS-10 11.30 0 00:48 42.74 0.26 18.13 0.06 0.57 0.38 5 Link-14 2.88 0 00:05 15.35 0.19 17.71 0.01 0.28 0.34 6 Link-16 24.99 0 00:30 46.94 0.53 19.26 0.03 1.04 0.69 7 Link-25 24.99 0 00:30 44.96 0.56 14.97 0.03 1.34 0.90 8 Link-29 25.11 0 00:29 31.48 0.80 14.71 0.04 1.50 1.00 9 Link-30 24.99 0 00:30 36.04 0.69 14.24 0.05 1.48 0.99 10 L-PIPE-2 11.30 0 00:48 27.43 0.41 11.97 0.06 0.79 0.53 11 L-PIPE-3 11.30 0 00:48 14.81 0.76 7.97 0.17 1.12 0.75 12 L-PIPE-4 11.30 0 00:47 14.93 0.76 7.37 0.11 1.23 0.82 13 L-PIPE5 11.31 0 00:47 34.18 0.33 9.87 0.06 0.98 0.65 14 L-PIPE6 11.30 0 00:47 19.78 0.57 14.98 0.11 0.74 0.59 15 L-PIPE6A 11.30 0 00:47 11.11 1.02 14.81 0.04 1.00 1.00 16 L-PIPE7 1.89 0 00:13 5.65 0.33 7.25 0.35 0.47 0.70 17 L-WEST OS STORM 2.89 0 00:05 3.54 0.82 12.42 0.33 0.42 0.63 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Inlet Input SN Element Inlet Manufacturer Number of Catchbasin Max (Rim)Inlet Initial Initial Grate ID Manufacturer Part Inlets Invert Elevation Depth Water Water Clogging Number Elevation Elevation Depth Factor (ft)(ft)(ft)(ft)(ft)(%) 1 EX-INLET OS-5 NEENAH FOUNDRY R-4894 1 7989.77 7999.78 10.01 7989.77 0.00 50.00 2 J-INLET-3 NEENAH FOUNDRY R-4895-2 1 7998.63 8007.20 8.57 7998.63 0.00 50.00 3 J-INLET6 FHWA HEC-22 GENERIC N/A 1 7999.50 8007.22 7.72 7999.50 0.00 50.00 4 J-INLET7 NEENAH FOUNDRY R-4826 1 8003.41 8008.00 4.59 8003.41 0.00 50.00 5 J-INLET8 FHWA HEC-22 GENERIC N/A 1 8032.50 8037.00 4.50 8032.50 0.00 50.00 Gorsuch Haus Lodge 100-Year Conceptual Drainage Design SE Project #:15101.06 Inlet Results SN Element Peak Peak Peak Flow Peak Flow Inlet ID Flow Lateral Intercepted Bypassing Efficiency Inflow by Inlet during Peak Inlet Flow (cfs)(cfs)(cfs)(cfs)(%) 1 EX-INLET OS-5 3.97 3.97 N/A N/A N/A 2 J-INLET-3 0.00 0.00 N/A N/A N/A 3 J-INLET6 2.27 1.16 1.37 0.91 60.15 4 J-INLET7 13.02 1.84 N/A N/A N/A 5 J-INLET8 3.26 3.26 1.89 1.37 58.02 NORWAY ISLAND, LLC GORSUCH HAUS MUDFLOW ANALYSIS #100-RCE-T38971 January 13, 2020 Norway Island, LLC Gorsuch Haus Mudflow Analysis This page intentionally left blank. Norway Island, LLC Gorsuch Haus Mudflow Analysis GORSUCH HAUS MUDFLOW ANALYSIS #100-RCE-T38971 January 13, 2020 PRESENTED TO PRESENTED BY Ms. Jean Coulter James DeFrancia Norway Island, LLC PO Box 12393 Aspen, CO 81612 Tetra Tech 3801 Automation Way, Suite 100 Fort Collins, CO 80026 P +1-970-223-9600 tetratech.com Prepared by: 1/13/2020 Name: Dai Thomas, Ph.D., P.E. Title: Senior Hydraulic Engineer Date Reviewed by: 1/13/2020 Name: Peggy Bailey, P.E. Title: Senior Hydraulic Engineer Date Norway Island, LLC Gorsuch Haus Mudflow Analysis This page intentionally left blank. Norway Island, LLC Gorsuch Haus Mudflow Analysis EXECUTIVE SUMMARY Norway Island, LLC is proposing to construct the Gorsuch Haus at the southern end of South Aspen Street, Aspen, CO. The Gorsuch Haus project includes construction of an 81-room hotel and removal of the existing lift building. Lift One Lodge Aspen, LLC is also proposing to construct the Lift One Lodge project along the east side of South Aspen Street, and approximately 400 feet downhill (north) of the Gorsuch Haus project. The Lift One Lodge project includes construction of two new buildings and the relocation of two existing buildings. Additional improvements include a new ski terminal, below grade parking structure and two of turnaround/drop off areas. Both projects include re-grading the hillslope for construction of drainage swales, realignment of the road and a ski run. The two Projects are separated by a narrow east-west right of way. The Projects are located within City of Aspen (City) mudflow hazard zone, and therefore, as part of City regulations (City of Aspen, 2014) and in accordance with Ordinance No. 19 (Series of 2016), a mudflow analysis is required to demonstrate that the Projects do not increase mudflow elevations on down-fan properties by more than 0.5 feet (under the updated mudflow regulations). Tetra Tech previously performed a mudflow analysis in support of Project Review approvals for both Gorsuch Haus and Lift One Lodge (Tetra Tech, 2018). Following the report, the City of Aspen requested that both projects be evaluated separately in support of the Project Detailed Review application. In addition, there were changes to the building design and grading that required updating the previous models. To perform the mudflow analysis, the City’s updated FLO-2D model was used to simulate the Existing conditions. Per application requirements, two Project conditions models were developed, that are referred to as the Gorsuch Haus conditions and the Lift One-Gorsuch Haus conditions. The Gorsuch Haus conditions represents only this project being constructed and that the buildings and grading on the Lift One property remain the same as Existing conditions. The Lift One-Gorsuch Haus conditions represents both projects being constructed at similar times. The Existing and two Project conditions models were run for the following hydrologic scenarios: • the 2-hour 25-year runoff hydrograph with sediment bulking up to 50-percent by volume • the 2-hour 100-year runoff hydrograph with sediment bulking up to 20-percent by volume The model output was evaluated by comparing the increase in mudflow elevation between the Existing and two Project conditions. For the Gorsuch Haus condition at the 25-year event, there is one element on the Lift One property that exceeds the 0.5-foot depth increase. To mitigate this, a debris flow wall is recommended along the south-east boundary of the Lift One property. The Lift One design includes a debris flow wall in this location to protect a building. If the Lift One project goes ahead, it is likely that this wall will remain. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page ii With the wall in place, the model results indicated that neither Project conditions will increase mudflow elevations by more than 0.5 feet on down-fan properties and that Gorsuch Haus Project can be constructed in compliance with the City’s updated regulations. The Gorsuch Haus model output was also used to develop design recommendations, which include openings (primarily doors and windows) that should be placed 3 feet above the mudflow elevation for all walls that will have direct impact forces from mudflow and debris, and 2 feet above the mudflow elevation for all walls impacted by mud flows moving laterally or are in the shadow of up-fan buildings. It is anticipated that the Lift One and Gorsuch Haus designs may be modified in the future. Tetra Tech will continue to work with the Sopris Engineering, LLC and the developers to ensure that any future changes will be in compliance with City’s mudflow regulations and the updated analysis and recommendations will be provided to the City. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page iii CONTENTS 1.0 INTRODUCTION .............................................................................................................................. 1 2.0 MUDFLOW ANALYSIS .................................................................................................................... 7 2.1 MUDFLOW CHARACTERIZATION AND PROCESSES ............................................................ 7 2.2 FLO-2D MODEL ........................................................................................................................ 11 2.2.1 Model Extents and Topography ................................................................................... 11 2.2.2 Channel and Overbank Roughness Values ................................................................. 11 2.2.3 Other Model Parameters .............................................................................................. 12 2.3 MUDFLOW HYDROGRAPHS ................................................................................................... 12 2.4 PROJECT CONDITIONS .......................................................................................................... 20 2.5 MUDFLOW MODEL RESULTS................................................................................................. 20 2.5.1 Existing Conditions ....................................................................................................... 20 2.5.2 Gorsuch Haus Conditions ............................................................................................. 24 2.5.3 Gorsuch Haus-With Mitigation Conditions .................................................................... 24 2.5.4 Gorsuch Haus-Lift One Conditions ............................................................................... 24 3.0 RECOMMENDATIONS .................................................................................................................. 36 4.0 REFERENCES ............................................................................................................................... 39 TABLES Table 2-1. Mudflow behavior as a function of sediment concentration (FLO-2D Manual, 2014) ............. 9 Table 2-2. Manning's n Roughness Values ............................................................................................ 15 Table 2-3. Summary of peak clearwater flow (cubic feet per second), clearwater flow and sediment volumes (acre-feet) and average sediment concentrations for the western and eastern mudflow sources ............................................................................................................ 15 Table 2-4. Comparison of peak bulked flows and sediment loads for the total inflow from the eastern mudflow source and into the study area ........................................................................ 21 Table 3-1.Freeboard and Safety Factor Recommendations (copied from FEMA, 2012)....................... 37 FIGURES Figure 1-1. Site Location Map. ............................................................................................................. 3 Figure 1-2. Lift One-Gorsuch Haus proposed design features. ........................................................... 4 Figure 1-3. Lift One-Gorsuch Haus site plan provided by Sopris Engineering, LLC. .......................... 5 Figure 1-4. City of Aspen mudflow zones. ........................................................................................... 6 Figure 2-1. Classification of hyper-concentrated sediment flows (modified from FLO-2D Manual, 2014). ............................................................................................................................... 10 Figure 2-2. Extents of the FLO-2D model and 1- and 10-foot interval contour mapping used to develop a Digital Terrain Model (DTM) of the study area................................................ 13 Figure 2-3. Land-use zones used to assign Manning’s n-values to the FLO-2D model. ................... 14 Figure 2-4. Location of mudflow sources applied to the FLO-2D model. .......................................... 17 Norway Island, LLC Gorsuch Haus Mudflow Analysis Page iv Figure 2-5. Clearwater hydrograph, sediment concentration (Cv) and bulked sediment hydrographs for the western mudflow source for the 2-hour, 25-year peak rainfall event. ............................................................................................................................... 18 Figure 2-6. Clearwater hydrograph, sediment concentration (Cv) and bulked sediment hydrographs for the western mudflow source for the 2-hour, 100-year peak rainfall event. ............................................................................................................................... 18 Figure 2-7. Clearwater hydrograph, sediment concentration (Cv) and bulked sediment hydrographs for the eastern mudflow source for the 2-hour, 25-year peak rainfall event. ............................................................................................................................... 19 Figure 2-8. Clearwater hydrograph, sediment concentration (Cv) and bulked sediment hydrographs for the eastern mudflow source for the 2-hour, 100-year peak rainfall event. ............................................................................................................................... 19 Figure 2-9. Maximum mudflow depth for the 2-hour 25-year rainfall event under Existing conditions. Note: The Gorsuch Haus footprint is shown for reference purposes and is not included in the model. ................................................................................................ 22 Figure 2-10. Maximum mudflow depth for the 2-hour 100-year rainfall event under Existing conditions. Note: The Gorsuch Haus footprint is shown for referenc e purposes. ........... 23 Figure 2-11. Predicted maximum mudflow depth for the 2-hour 25-year rainfall event under the Gorsuch Haus conditions. ............................................................................................... 26 Figure 2-12. Predicted increase in mudflow elevation between Gorsuch Haus and Existing conditions for the 2-hour 25-year rainfall event. .............................................................. 27 Figure 2-13. Predicted maximum mudflow depth for the 2-hour 100-year rainfall event under the Gorsuch Haus conditions. ............................................................................................... 28 Figure 2-14. Predicted increase in mudflow elevation between Gorsuch Haus and Existing conditions for the 2-hour 100-year rainfall event. ............................................................ 29 Figure 2-15. Predicted maximum mudflow depth for the 2-hour 25-year rainfall event under the Gorsuch Haus conditions with the debris flow wall. ........................................................ 30 Figure 2-16. Predicted maximum mudflow depth for the 2-hour 100-year rainfall event under the Gorsuch Haus conditions with the debris flow wall. ........................................................ 31 Figure 2-17. Predicted maximum mudflow depth for the 2-hour 25-year rainfall event under the Gorsuch Haus-Lift One conditions. .................................................................................. 32 Figure 2-18. Predicted maximum mudflow depth for the 2-hour 100-year rainfall event under the Gorsuch Haus-Lift One conditions. .................................................................................. 33 Figure 2-19. Predicted increase in mudflow elevation between Gorsuch Haus-Lift One and Existing conditions for the 2-hour 25-year rainfall event. ................................................ 34 Figure 2-20. Predicted increase in mudflow elevation between Gorsuch Haus-Lift One and Existing conditions for the 2-hour 100-year rainfall event. .............................................. 35 Figure 3-1. Predicted increase in mudflow elevation between Gorsuch Haus-Lift One and Existing conditions for the 2-hour 100-year rainfall event. .............................................. 38 Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 1 1.0 INTRODUCTION Norway Island, LLC is proposing to construct Gorsuch Haus at the southern end of South Aspen Street, Aspen, CO (Figure 1-1).The Gorsuch Haus project includes construction of an 81-room hotel and removal of the existing lift building (Figure 1-2). Lift One Lodge Aspen, LLC is proposing to construct the Lift One Lodge project along the east side of South Aspen Street, and approximately 400 feet downhill of the Gorsuch Haus project (Figure 1-2). A similar mudflow analysis comparing Existing conditions with and without the Gorsuch Haus development will be prepared for the Lift One Lodge Detailed Review application. The Lift One project includes construction of two new buildings and relocation of two existing as well as a couple of turnarounds/drop off areas. The City of Aspen will acquire the Dolinsek Life Estate property which will serve as a portion of the ski way and skier milling area. No buildings are currently being considered on the Dolinsek Parcel. Additional improvements include a new ski terminal, below grade parking structure and a couple of turnaround/drop off areas. Both projects include some re-grading of the hillslope. The two developments are separated by an east-west right of way. The Existing conditions and Gorsuch Haus building footprints and grading were provided by Sopris Engineering, dated October 13, 2019. The Lift One-Gorsuch Haus Site Plan with building footprints and grading were provided by Sopris Engineering, dated May 25, 2018 (Figure 1-3). The Gorsuch Haus and Lift One projects are located within City of Aspen (City) mudflow hazard zone (blue and yellow zones) (Figure 1-4). Therefore, as part of City regulations (City of Aspen, 2014) and in accordance with Ordinance No. 19 (Series of 2016), a mudflow analysis is required to demonstrate that the Projects do not increase mudflow elevations on down-fan properties by more than 0.5 feet. Tetra Tech, under a subcontract agreement with Wright Water Engineers, developed a FLO-2D model for the City. The model was developed for the following purposes: (1) to update the mudflow regulations, (2) to be the City’s official FLO-2D model, and (3) to be provided to consultants to perform mudflow studies. The updated mudflow regulations were expected to have been adopted by the City in 2019, but as of yet, they have not been. The City approved the use of the updated regulations for this study on the basis that they will be in effect prior to submitting a construction permit to the City (personal communication, April Long, City of Aspen, October 2018). To perform the mudflow analysis, the City’s updated FLO-2D model was used to simulate the Existing conditions. Per Project Detailed Review requirements the following two Project conditions models were developed in support of the Gorsuch Haus Development: • Gorsuch Haus conditions which represents only Gorsuch Haus being constructed and that the buildings and grading on the Lift One property are the same as Existing conditions. • Gorsuch Haus-Lift One conditions that represents both projects being constructed at similar times. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 2 The Existing and two Project conditions models were run for the following hydrologic scenarios: • the 2-hour 25-year runoff hydrograph with sediment bulking up to 50-percent by volume • the 2-hour 100-year runoff hydrograph with sediment bulking up to 20-percent by volume The model output was evaluated by comparing the increase in mudflow elevation between the Existing and two Project conditions. The model output was used to develop design recommendations for the Gorsuch Haus project. Design recommendations for the Lift One project are not part of this study. It is likely that the Lift One design will change, and the mudflow analysis will be updated. Design recommendations for Lift One will developed as part of a future study. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 3 Figure 1-1. Site Location Map. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 4 Figure 1-2. Lift One and Gorsuch Haus proposed design features. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 5 Figure 1-3. Lift One-Gorsuch Haus site plan provided by Sopris Engineering, LLC. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 6 Figure 1-4. City of Aspen mudflow zones. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 7 2.0 MUDFLOW ANALYSIS The City of Aspen Mudflow Regulations apply to all new development and re-development projects within the red, blue or yellow mudflow zones, as shown on Figure 7.1, Chapter 7-Mudflow Analysis, of the City’s Urban Runoff Management Plan, dated November 2014 (Mudflow Regulations) (Figure 1-2). As previously mentioned, the City’s mudflow regulations are in the process of being updated and the City has allowed the new regulations to be applied to this study. The proposed mudflow regulations will mostly likely recommend the following six-step procedure for evaluating mudflows. 1. Obtain current official FLO-2D model files from the City of Aspen. This model was developed by WWE (2017) and is referred to as the Existing conditions model. 2. Run the Existing conditions model for the 2-hour 25-year rainfall hydrograph with sediment bulking up to 50-percent by volume, and the 2-hour, 100-year rainfall hydrograph with sediment bulking up to the 20-percent by volume. 3. Modify the geometry input. Modify the existing conditions model to reflect the project conditions and run the model over the 100-year, 2-hour rainfall hydrograph. This model is referred to as the Project conditions model. 4. Compare predicted mud/water surface elevations with pre-project (Existing) conditions. Evaluate the down-fan impacts by comparing the increase in mud depths under Project conditions. The proposed regulations allow an increase in mudflow elevation of up to 0.5- feet under Project conditions on areas that are also inundated under Existing conditions. 5. Evaluate static and dynamic mudflow forces and identify potential mitigation measures. If necessary, (1) develop recommendations to mitigate offsite impacts insuring project conditions do not exceed existing conditions (within a 0.5 ft tolerance) on down-fan properties, (2) provide grading recommendations where beneficial for reducing mudflow impacts, and (3) develop recommendations to mitigate onsite mudflow impacts and loading forces for structural design. 6. Prepare submittals to City. 2.1 MUDFLOW CHARACTERIZATION AND PROCESSES Hyper-concentrated sediment flows (mudflows and mud floods) are part of a continuum in the “physics of flowing water and sediment movement that ranges from clear water flow to mass wasting processes (landslides)” (SLA and O’Brien, 1989). In general, the sediment-transport characteristics in the continuum range from suspended and bed load transport in water floods to mass wasting in landslide events. The National Research Council Committee (NRC, 1982) proposed four categories to delineate this continuum: water floods, mud floods, mudflows, and landslides (Table 2-1). The bounds of each of these categories can be approximated based on the fluid properties, and in particular by the sediment concentration (by volume) of the fluid (Figure 2-1).The sediment concentration of fluid is defined as the ratio of the sediment volume to the water volume and is given by: CV = Volume of Sediment / (Volume of Water + Volume of Sediment) The continuum indicates that water floods are mostly comprised of water with some sediment (low concentration of sediment), whereas, landslides are mostly comprised of bulk sediment with some water (high concentration of sediment). The concentration of the sediment is an important Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 8 component in determining the physical processes that govern the behavior of the fluid-sediment mixture in each of these categories. For example, the flow characteristics of a mud flood are dominated by the turbulent and viscous forces within the fluid matrix; whereas, movement of a landslide is dominated by the dispersive stresses and particle friction. This study focuses on the sediment-transport characteristics of the mud flood and mudflow categories; however, a brief description of the sediment transport characteristics of the water floods and land sliding events is presented for the purpose of describing the bounding categories. Flood flows generally have sediment concentrations of less than 20 percent (by volume). They are essentially water floods with high bed load and suspended loads where the bed load may be affected by the high concentration of suspended load (i.e., fine sediment wash load). The sediment-transport characteristics of water floods are modeled using conventional bed- and suspended-load formulas and methodologies. Landslides generally have sediment concentrations greater than 55 percent (by volume) and are considered as bulk solid movement as opposed to fluid motion. Landslides may range from slow- moving earth flow and creeping soil masses to rapid rotation or slippage failures. Hyper-concentrated sediment flows are defined as flood events with sediment concentrations that range between approximately 20 and 55 percent by volume, however, the sediment concentration for a given event is generally considered to be between 20 and 45 percent (O’Brien, 2004). The fine sediment concentration (silt, clay and fine sands in the fluid matrix) controls the properties of the fluid, including, viscosity, density, and yield stress. Mudflows are non-Newtonian and they have much higher viscosities and densities compared to water flows. These properties result in mudflows having significantly slower velocities compared to water floods on the same slope. The fine sediments increase the density of the fluid matrix, which increases the buoyancy of sediments thereby creating conditions that allow gravel to boulder-sized material to be transported near the flow surface by mudflows. The yield stress is a measure of the internal fluid resistance to flow and affects both the initiation and cessation of flows. For the purposes of this report, all hyper- concentrated sediment flows (mud floods and mudflows) will be referred to as mudflows. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 9 Table 2-1. Mudflow behavior as a function of sediment concentration (FLO-2D Manual, 2014) Event Sediment Concentration Flow Characteristics by Volume by Weight Landslide 0.65 - 0.80 0.83 - 0.91 Will not flow; failure by block sliding 0.55 - 0.65 0.76 - 0.83 Block sliding failure with internal deformation during the slide; slow creep prior to failure Mudflow 0.48 - 0.55 0.72 - 0.76 Flow evident; slow creep sustained mudflow; plastic deformation under its own weight; cohesive; will not spread on level surface 0.45 - 0.48 0.69 - 0.72 Flow spreading on level surface; cohesive flow; some mixing Mud Flood 0.40 - 0.45 0.65 - 0.69 Flow mixes easily; shows fluid properties in deformation; spreads on horizontal surface but maintains an inclined fluid surface; large particle (boulder) setting; waves appear but dissipate rapidly 0.35 - 0.40 0.59 - 0.65 Marked settling of gravels and cobbles; spreading nearly complete on horizontal surface; liquid surface with two fluid phases appears; waves travel on surface 0.30 - 0.35 0.54 - 0.59 Separation of water on surface; waves travel easily; most sand and gravel has settled out and moves as bed load 0.20 - 0.30 0.41 - 0.54 Distinct wave action; fluid surface; all particles resting on bed in quiescent fluid condition Water Flood < 0.20 < 0.41 Water flood with conventional suspended load and bed load Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 10 Figure 2-1. Classification of hyper-concentrated sediment flows (modified from FLO-2D Manual, 2014). The sediment matrix of a hyper-concentrated flow is non-homogeneous, and the sediment properties change significantly as they flow down steep watershed channels or across alluvial fans. As the mudflow moves over the alluvial fan, dewatering of the fluid matrix can occur by infiltration and escapement to the surface. This may further increase the concentration of the hyper-concentrated sediment flows and alter the transport characteristics of the flow. “Almost all hyper-concentrated sediment flows are fully turbulent, unsteady and non-uniform, and are characterized by surging, flow cessation, blockage, and roll waves” (SLA and O’Brien, 1989). During a mudflow event, the average sediment concentration over the duration of the hydrograph generally ranges between 20 and 35 percent by volume with peak concentrations approaching 50percent (Figure 2-1 and Table 2-1). Most watersheds with a history of mudflow events will eventually develop a sediment supply in the channel bed such that even relatively small rainfall-runoff storms may generate mudflow surges. In general, mudflows have a distinct pattern of flood evolution. Initially, clear water flows from the basin rainfall-runoff may arrive at the fan apex. This may be followed by a surge or frontal wave of mud and debris (40- to 50-percent concentration by volume). When the peak arrives, the average sediment concentration generally decreases to the range of 30 to 40 percent by volume. On the falling limb of the hydrograph, the sediment concentration decreases due to the reduced availability of sediment; however, surges of higher sediment concentration may occur. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 C on ce ntrati o n by Vo lu me (C V) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 C o ncen tra tio n by We i gh t (CW) Water Flow Transition Zone M ud Flood M u d Flo w L a n d s li d e Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 11 2.2 FLO-2D MODEL FLO-2D is a 2-dimensional (2-D) hydraulic model that was developed to perform both clearwater, sediment-transport and hyper-concentrated sediment flow-routing in channels and/or on alluvial fans with an unconfined flow path. The model utilizes a volume conservation scheme to simulate both sub- and super-critical flows in the channel or floodplains, as well as flows exiting from the channel to the floodplain and vice versa. Overland flow is modeled using a 2-D diffusive wave approximation of the momentum equation. A central difference routing scheme with eight potential flow directions is used to simulate the progression of the flood wave hydrograph over a system of square grids. The FLO-2D model contains several components that are used to represent and model the complex topography and processes, including: channel-floodplain flow exchange, loss of storage due to buildings, flow obstructions, simulation of hydraulic structures, simulation of street flow, and simulation of hyper-concentrated sediment flows (mudflows). Hyper-concentrated sediment flow is simulated by the FLO-2D model using a quadratic rheological model that includes viscous stress, yield stress, turbulence, and dispersive stress terms as a function of sediment concentration. FLO-2D does not have the ability to model unsteady phenomena such as surging. It also assumes a rigid boundary, and therefore, does not model channel, overbank or fan degradation. 2.2.1 MODEL EXTENTS AND TOPOGRAPHY The City of Aspen FLO-2D model covers Aspen Mountain and the area of the City located between the base of the mountain and the Roaring Fork River (Figure 2-2). The model has a 20-foot grid size and contains 165,214 grid cells. The Grid Developer System (GDS), which is part of the FLO-2D model, was used to assign elevations to each grid element using a Digital Terrain Model (DTM) developed from topographic mapping provided by the City. The topographic mapping consists of 1- and 10-feet interval contour mapping that was based on a LiDAR survey performed for the City in 2008. The 1-foot interval contour mapping data covered City and part of the lower mountain and the 10-feet interval contour mapping covered the upper part of the mountain (Figure 2-2). The 1- and 10-foot mapping was used to create a DTM with 3-foot resolution which was used to assign elevations to the grid elements. The City is at an elevation of approximately 7,900 feet and the elevation at the top of the mountain is approximately 11,200-feet, generating slopes greater than 45 degrees in many areas. The Existing conditions FLO-2D model was updated with 2018 topographic survey data provided in the Lift 1 design plans by Sopris Engineering. The City’s FLO-2D model is in the National Geodetic Vertical Datum of 1929 (NGVD29). For this study, the model was converted to the National American Vertical Datum of 1988 (NAVD88) to be consistent with the design plans. 2.2.2 CHANNEL AND OVERBANK ROUGHNESS VALUES Manning’s n-values roughness polygons were delineated in ArcGIS, a Geographic Information Software (GIS) program, to represent zones with similar roughness characteristics based on 2015 aerial photography. The individual zones were visually identified based on vegetation type and density, and land-uses that include grassland/ski areas, forested areas, mine tailings, and Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 12 urbanized areas. The specific Manning’s n roughness values were assigned based on guidance in the FLO-2D manual (FLO-2D, 2015). The n-values assigned to these areas ranged from 0.02 for roads, which are relatively smooth, to 0.40 for dense forest and Mine Tailings that typically have a very rough surface. Land classifications and associated n-values are provided in Table 2-2 and the land use mapping is shown in Figure 2-3. 2.2.3 OTHER MODEL PARAMETERS Other model parameters typically applied to FLO-2D models include width reduction factors (WRFs), area reduction factors (ARFs), street elements and levees. The WRF’s and ARF’s are assigned to the FLO-2D grid elements to represent the blockage of flow paths and reduction in storage that mostly occur due to the presence of buildings. Width reduction factors are applied to represent the blockage of flow through the side of an element, while ARFs represent the loss of floodplain storage volume due to the buildings. For example, a wall might obstruct 40 percent of the flow width of a grid element side and a building could cover 75 percent of the same grid element. An ArcGIS shapefile of the building outlines and streets was provided by the City. The building shapefile was used to assign the ARF’s and WRF’s to grid elements using the model development tools in FLO-2D. The site building footprint for Existing and two Project conditions was based on the plans provided by Sopris Engineering and were used to assign the ARF and W RF’s. Streets are a specific option in FLO-2D used to represent the elevation and roughness characteristics of the roadways. Street elements have different conveyance and storage properties compared to the floodplain elements. Street elements are important as they act as conduits for conveying flood flows and have the ability to store sediment. They are applied when width of the street is less than the width of the element. In the model developed for this study, the streets are wider than the 20-foot elements. Thus, to better represent the streets in the model, the street grid elements were assigned Manning’s n-values of 0.02 and no infiltration capacity. The proposed walls shown in Figure 1-2 were represented using the levee feature in the model. 2.3 MUDFLOW HYDROGRAPHS Two potential mudflow sources were applied to the model. The primarily mudflow source originates from Pioneer Gulch (Figure 2-4), this is referred to as the eastern source. The second source is located to the west of the stand of trees located uphill (south) of the proposed Gorsuch Haus building. The hydrograph for the western source has a peak clearwater flow of 2.5 cfs for the 25-year event and 3.6 cfs for the 100-year events, and the peak flows for the eastern source are 52 cfs for the 25-year event and 109 cfs for the 100-year event (Table 2-3, Figure 2-5 through Figure 2-8) (WWE, 2017). Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 13 Figure 2-2. Extents of the FLO-2D model and 1- and 10-foot interval contour mapping used to develop a Digital Terrain Model (DTM) of the study area. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 14 Figure 2-3. Land-use zones used to assign Manning’s n-values to the FLO-2D model. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 15 Table 2-2. Manning's n Roughness Values Land Use Manning’s n Roughness Value Urban/Structures 0.04 Roads/Streets 0.02 Mine Tailing 0.40 Grassland/Ski Runs 0.20 Light Forest 0.30 Medium Forest 0.35 Dense Forest 0.40 Table 2-3. Summary of peak clearwater flow (cubic feet per second), clearwater flow and sediment volumes (acre-feet) and average sediment concentrations for the western and eastern mudflow sources Rainfall Event Peak Clearwater Flow (cfs) Clearwater Volume (ac- ft) Peak Bulked Flow (cfs) Bulked Volume (ac-ft) Sediment Volume (ac-ft) Average Conc. Western Mudflow Source 25-YR 2.5 0.045 3.1 0.056 0.011 0.20 100-YR 3.6 0.075 4.5 0.094 0.019 0.20 Eastern Mudflow Source 25-YR 52 2.6 79 3.81 1.23 0.32 100-YR 109 4.99 136 6.23 1.25 0.20 The clearwater hydrographs were bulked with sediment using a developed sediment concentration (by volume, CV) hydrograph to represent the mudflow hydrograph. The total volume of the water and sediment in a mudflow can be determined by multiplying the clearwater volume by the bulking factor, where the bulking factor is defined by: BF = 1/(1 - CV) For example, a sediment concentration of 10 percent (CV=0.10) creates a bulking factor of 1.11, indicating the flood volume is 11 percent greater than if the flood was considered to be only water. The sediment concentration hydrographs for the western source have a constant value of 20- percent by volume for the 25-year and 100-year events that reflects the small drainage area and limited sediment supply from the uphill basin (Figure 2-5 and Figure 2-6)(WWE, 2017). Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 16 The sediment concentration hydrograph for the eastern source for the 25-year event represents the likely variation in sediment concentration throughout the storm hydrograph and has the following characteristics (Figure 2-7): • The initial rising limb and the last part of the recessional limbs of the hydrographs have a sediment concentration of 20 percent, which corresponds to the minimum concentration for a mudflow. • The steep rising limb of the hydrograph is bulked to a maximum concentration of 5 0 percent to simulate the frontal wave of the mudflow. The peak of the sediment concentration hydrograph occurs 6 minutes before the peak of the clearwater hydrograph. • The sediment concentration at the peak of the clearwater hydrograph is less than the peak sediment concentration in order to simulate water dilution. • The average sediment concentration over the hydrograph is approximately 32 percent. For the eastern source, the 100-year event has a constant sediment concentration of 20-percent by volume (Table 2-3, Figure 2-8). Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 17 Figure 2-4. Location of mudflow sources applied to the FLO-2D model. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 18 Figure 2-5. Clearwater hydrograph, sediment concentration (Cv) and bulked sediment hydrographs for the western mudflow source for the 2-hour, 25-year peak rainfall event. Figure 2-6. Clearwater hydrograph, sediment concentration (Cv) and bulked sediment hydrographs for the western mudflow source for the 2-hour, 100-year peak rainfall event. 0 0.05 0.1 0.15 0.2 0.25 0 1 2 3 4 5 0 0.5 1 1.5 2 2.5 3 Se d i m e n t C o n c e n t r a t i o n ( C v , b y V o l u m e ) Fl o w ( c f s ) Time (hrs) Clearwater Flow Bulked Flow Sediment Concentration 0.00 0.05 0.10 0.15 0.20 0.25 0 1 2 3 4 5 0 0.5 1 1.5 2 2.5 3 Se d i m e n t C o n c e n t r a t i o n ( C v , b y V o l u m e ) Fl o w ( c f s ) Time (hrs) Clearwater Flow Bulked Flow Sediment Concentration Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 19 Figure 2-7. Clearwater hydrograph, sediment concentration (Cv) and bulked sediment hydrographs for the eastern mudflow source for the 2-hour, 25-year peak rainfall event. Figure 2-8. Clearwater hydrograph, sediment concentration (Cv) and bulked sediment hydrographs for the eastern mudflow source for the 2-hour, 100-year peak rainfall event. 0 0.1 0.2 0.3 0.4 0.5 0.6 0 10 20 30 40 50 60 70 80 90 100 0 0.5 1 1.5 2 2.5 3 Se d i m e n t C o n c e n t r a t i o n ( C v , b y V o l u m e ) Fl o w ( c f s ) Time (hrs) Clearwater Flow Bulked Flow Sediment Concetration 0.00 0.05 0.10 0.15 0.20 0.25 0 20 40 60 80 100 120 140 0 0.5 1 1.5 2 2.5 3 Se d i m e n t C o n c e n t r a t i o n ( C v , b y V o l u m e ) Fl o w ( c f s ) Time (hrs) Clearwater Flow Bulked Flow Sediment Concentration Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 20 2.4 PROJECT CONDITIONS The two proposed project conditions model were developed by modifying the Existing conditions model to represent the project building footprints, walls, and regrading as shown in the design plans (Figure 1-2 and Figure 1-3). The ARF and WRF factors were adjusted to reflect the building footprints (Figure 1-2). The levee option was used to represent the proposed walls. The elevation of the top of some walls was not specified in the plans, and so, the wall heights were set sufficiently high to prevent overtopping. The grid elevations were modified to reflect the grading show in the design plans (Figure 1-2). The grading includes a new road alignment along the east side of Gorsuch Haus. The road grading is mostly excavation into the existing hillside. The excavation ranges up to about 5 feet in the middle section of the road. 2.5 MUDFLOW MODEL RESULTS The Existing and two Project conditions models were run over the same 25- and 100-year peak flow hydrographs, and the model output was used to map and evaluate the changes in mudflow elevations. 2.5.1 EXISTING CONDITIONS The Existing conditions model indicates that mudflow from the eastern source separates into two flow paths on either side of the Mountain Queen, with the majority of the flow to the east of the Mountain Queen (Figure 2-9). At the 25-year event, approximately 69-percent of the sediment load passes to the east of the Mountain Queen and 21-percent to the west. At the 100-year event, approximately 53-percent and 30-percent of the sediment passes to the east and west of the Mountain Queen, respectively (Table 2-4). The mudflow to the east of the Mountain Queen is conveyed along the open ground between the Mountain Queen and the town homes located along South Mill Street, as well as in a northerly direction along South Mill Street (Figure 2-9). The majority of the mudflow to the west of the Mountain Queen, is conveyed in a swale located about 15 feet from the building. The flow continues in a northerly direction across the project area and across Dean Street (aligned approximately east-west) between South Aspen Street and South Monarch Street. The mudflow from the western source flows in an approximately north-easterly direction towards the stand of trees. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 21 Table 2-4. Comparison of peak bulked flows and sediment loads for the total inflow from the eastern mudflow source and into the study area Rainfall Event Peak Bulked Inflow (cfs) Bulked Volume (ac-ft) Total Sediment Volume (ac-ft) 25-Year Peak Flow Event Total Inflow 80.4 3.81 1.24 West of Mountain Queen 21.2 0.79 (21%) 0.25 East of Mountain Queen 50.6 2.61 (69%) 0.91 100-Year Peak Flow Event Total Inflow 136.2 6.33 1.25 West of Mountain Queen 38.2 1.89 (30%) 0.38 East of Mountain Queen 71.7 3.38 (53%) 0.68 At the 25-year event, the maximum flow depths in the project area range up to 2.5 feet along the west side of the Mountain Queen and up to 4.5 feet at the Caribou Condominiums (701 S. Monarch Street) located immediately north of the Mountain Queen (Figure 2-9). In general, the majority of the flows depths in the project area are less than 0.5 feet. Outside of the project area, the maximum depths of up to 6.5 feet occur along S. Mill Street near the St Regis Hotel (Figure 2-9). At the 100-year event, the maximum flow depths in the project area range up to 2.5 feet along the west side of the Mountain Queen. Just outside of the project area, the maximum depths of up to 9 feet occur along South Mill Street (Figure 2-10). Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 22 Figure 2-9. Maximum mudflow depth for the 2-hour 25-year rainfall event under Existing conditions. Note: The Gorsuch Haus footprint is shown for reference purposes and is not included in the model. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 23 Figure 2-10. Maximum mudflow depth for the 2-hour 100-year rainfall event under Existing conditions. Note: The Gorsuch Haus footprint is shown for reference purposes. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 24 2.5.2 GORSUCH HAUS CONDITIONS The City regulations require an evaluation of the increase in flow depth. Due to the grading changes, there are instances where the ground elevation is higher under Project conditions compared to Existing condition, but the depth is less. For comparison purposes, the increase in water-surface elevation between the project and existing conditions is shown as a surrogate for increase in depth. As an example, if the ground elevation increases by 1-foot, and the depth increases by 0.1-foot, this will show as an increase in water-surface elevation of 1.1- foot. It is important to recognize that the water-surface elevation increases represent the maximum increase over the duration of the hydrograph, and not the water-surface elevation at the end of the simulation. Under the Gorsuch Haus conditions, the predicted depths at the 25-year event are very similar to the Existing conditions, except along the middle section of the proposed road adjacent to Gorsuch Haus (Figure 2-11). The Gorsuch Haus model at the 25-year event predicts an increase in water-surface elevation of 0.9 feet at two elements on the Lift One property (Figure 2-12).The model predicts an increase of about 0.8 feet at two elements on East Dean Street and South Monarch Street (Figure 2-12). The predicted flows depths at the 100-year event are very similar to the Existing conditions (Figure 2-13) and the model did not predict an increase in mudflow water-surface elevation on downfan properties (Figure 2-14). To mitigate the increase in depth at the 25-year event, it is recommended to construct a debris flow wall along the right of way as discussed in the next section. 2.5.3 GORSUCH HAUS-WITH MITIGATION CONDITIONS The proposed debris flow wall is located approximately 20-feet up hill of a wall proposed for the Gorsuch-Lift One condition. The wall for the Gorsuch-Lift One condition was sited to protect the uphill side of the proposed building. If the Lift-One project is constructed, it is likely that the wall will remain to protect the Lift One building. The proposed debris flow wall is 50-feet long and 5 feet high. The predicted flow depth on the uphill side of the wall is 1.5 feet under the 25- and 100-year events. Under the 25-year event and 100-year events with the wall in place, there are no down fan impacts on neighboring properties (Figure 2-15 and Figure 2-16). There is one element on East Dean Street and One Element on South Monarch Street with a depth increase of about 0.8 feet; these increases are on the street and not on private property. 2.5.4 GORSUCH HAUS-LIFT ONE CONDITIONS The Gorsuch Haus-Lift One Project conditions model for the 25- and 100-year events predicts very similar depths and extents compared to the Existing conditions (Figure 2-17 and Figure 2-18). At the 25-year event, there is an increase in mudflow elevation on the Dolinesk property in the location of a proposed stormwater swale (Figure 2-19). At the 100-year event, there are increases in mudflow elevation on the Dolinesk and Lift One properties, particularly near the northwest corner of the Lift One property (near the corner of South Aspen Street and East Dean Street)(Figure 2-20). These increases are due to ponding behind a proposed wall. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 25 The increase in mudflow elevations do not exceed the allowable 0.5-foot tolerance on any neighboring properties at the 25- and 100-year peak flow events. Therefore, the proposed designs meet the City’s proposed mudflow regulations. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 26 Figure 2-11. Predicted maximum mudflow depth for the 2-hour 25-year rainfall event under the Gorsuch Haus conditions. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 27 Figure 2-12. Predicted increase in mudflow elevation between Gorsuch Haus and Existing conditions for the 2-hour 25-year rainfall event. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 28 Figure 2-13. Predicted maximum mudflow depth for the 2-hour 100-year rainfall event under the Gorsuch Haus conditions. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 29 Figure 2-14. Predicted increase in mudflow elevation between Gorsuch Haus and Existing conditions for the 2-hour 100-year rainfall event. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 30 Figure 2-15. Predicted maximum mudflow depth for the 2-hour 25-year rainfall event under the Gorsuch Haus conditions with the debris flow wall. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 31 Figure 2-16. Predicted maximum mudflow depth for the 2-hour 100-year rainfall event under the Gorsuch Haus conditions with the debris flow wall. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 32 Figure 2-17. Predicted maximum mudflow depth for the 2-hour 25-year rainfall event under the Gorsuch Haus-Lift One conditions. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 33 Figure 2-18. Predicted maximum mudflow depth for the 2-hour 100-year rainfall event under the Gorsuch Haus-Lift One conditions. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 34 Figure 2-19. Predicted increase in mudflow elevation between Gorsuch Haus-Lift One and Existing conditions for the 2-hour 25-year rainfall event. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 35 Figure 2-20. Predicted increase in mudflow elevation between Gorsuch Haus-Lift One and Existing conditions for the 2-hour 100-year rainfall event. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 36 3.0 RECOMMENDATIONS The FLO-2D output was used to develop design recommendations which are based on the City of Aspen Mudflow Regulations, Chapter 7 (2014) and FEMA design guidelines (2012). The following are general recommendations for mudflows. Building penetrations such as a windows or doors should be set with freeboard above the design depth. A minimum of 3 feet of freeboard is typically recommended by FEMA for surging waves which would include all walls that will have direct impact forces from mudflow and debris (e.g. the uphill side of Gorsuch Haus and the debris flow wall near the south east corner of the Lift One property) (Table 3-1). A minimum of 2 feet of freeboard is typically recommended for all walls with minor surging such as walls impacted by mud flows moving laterally or that are in the shadow of up- fan buildings (Table 3-1). If the design depth cannot be achieved, then impact resistant glass could be considered for windows with the capabilities to withstand the required static and dynamic forces as discussed below. In the case of doors and garage doors, two conditions should be considered if the design depth cannot be achieved. First, the door should be designed for static and dynamic loading and include provisions for seepage; secondly, there should be an alternative exit for people to leave the building. For static and dynamic design recommendations, we apply the loading criteria provided in the City of Aspen Mudflow Regulations, Chapter 7 (2014). The freeboard depth is computed using the following FEMA recommend freeboard equation: F=(d1.5Qdesign – dQdesign) + V2/2g Equation 1 where: F=recommended freeboard V= velocity of flow (ft/s) g = acceleration of gravity (ft/s2) d1.5Qdesign = depth of flooding from a discharge 50 percent greater than the design discharge (ft) dQdesign= depth of flooding from design discharge (ft) For the Gorsuch Haus project, there is potential for mudflow to deposit on the uphill side of the building. Based on Equation 1, the recommended freeboard depth is 0.1, which is less than the minimum requirements indicated in Table 3-1. Therefore, the freeboard specifications in Table 3-1 should be applied. Along the uphill side of Gorsuch Haus, which has direct impact forces, a freeboard of 3 feet is recommended. At locations where the mudflow is conveyed laterally to the buildings and or the buildings are located in the shadow of another building, a 2-foot freeboard is recommended. It is recommended to construct a debris flow wall along the south-east boundary of the Lift One property to prevent an increase in mudflow elevation along the property boundary. Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 37 Design recommendations for the Lift One project are not part of this study. It is likely that the Lift One design will change, and the mudflow analysis will be updated. Design recommendations for Lift One will developed as part of a future study. Table 3-1.Freeboard and Safety Factor Recommendations (copied from FEMA, 2012). Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 38 Figure 3-1. Predicted increase in mudflow elevation between Gorsuch Haus-Lift One and Existing conditions for the 2-hour 100-year rainfall event. Max Depth 1.5’ Max Depth 0.1’ Norway Island, LLC Gorsuch Haus Mudflow Analysis Page 39 4.0 REFERENCES City of Aspen, 2014. Urban Runoff Management Plan. November. Federal Emergency Management Agency (FEMA), 2012. Engineering Principals and Practices for Retrofitting Flood-Prone Residential Structures. Appendix D – Alluvial Fan Flooding. FLO-2D, Pro, 2014. FLO-2D Software, Inc. Nutrioso, Arizona. National Research Council, 1982. “Selecting a methodology for delineating mudslide hazard areas for the National Flood Insurance Program.” National Academy of Sciences report by the advisory Board on the Built Environment, Washington, D.C. O’Brien, J.S., 2004. Simulating Mudflow Guidelines. Guidelines provided with FLO-2D model. O’Brien, J.S., and Lenzotti& Fullerton Consulting Engineers, Inc., 1989. Flood Hazard Delineation on Alluvial Fans and Urban Floodplains. Simons, Li and Associates, Inc. and O’Brien, J.S., 1989. Flood Hazard Delineation for Cornet Creek, Telluride, Colorado. Submitted to the Federal Emergency Management Agency, Region VIII, March. Tetra Tech, 2018. Lift One Lodge and Gorsuch Haus Mudflow Analysis. Prepared for Lift One Lodge Aspen LLC and Norway Island LLC. November, p37. Wright Water Engineers, 2017. Aspen Mud and Debris Flow Assessment. Prepared for the City of Aspen.