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Home My WebLink AboutFile Documents.533 W Hallam St.0285.2018 (93).ARBK DRAINAGE REPORT FOR DUNCAN SKIHAUS 533 W. HALLAM STREET, ASPEN, CO I hereby affirm that this report and the accompanying drawings for the analysis of 533 W. Hallam Street, Aspen, Colorado was prepared under my direct supervision for the owners thereof in accordance with the provisions of the City of Aspen Urban Runoff Management Plan with proposed variances and exceptions listed thereto. I understand that it is the policy of the City of Aspen that the City of Aspen does not and will not assume liability for drainage facilities designed by others. Permit #: 0285.2018.ARBK February 10, 2020 Rick Barth, P.E. 36749 Prepared by 118 West Sixth Street, Suite 200 Glenwood Springs, CO 81601 970.945.1004 970.945.5948 fax 02/28/2020 Reviewed by Engineering 03/20/2020 8:19:46 AM "It should be known that this review shall not relieve the applicant of their responsibility to comply with the requirements of the City of Aspen. The review and approval by the City is offered only to assist the applicant's understanding of the applicable Engineering requirements." The issuance of a permit based on construction documents and other data shall not prevent the City of Aspen from requiring the correction of errors in the construction documents and other data. 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design i DRAINAGE REPORT FOR DUNCAN SKIHAUS 533 W. HALLAM STREET, ASPEN, CO REVIEWED BY RICK BARTH SGM Project # 2018-292.001 I:\2018\2018-292-DuncanSkihaus\001\E-Reports\SGM\Dun-Drainage-Report\docs\Duncan- Drainage-Report.docx 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design ii TABLE OF CONTENTS 1.0 Existing Site 3 1.1 Description of Existing Site 3 1.2 Description of Existing Drainage 3 2.0 Proposed Project 3 3.0 Proposed Basins 4 3.1 Basin A (sub-basins 1 & 2) 4 Sub-basin 1 5 Sub-basin 2 5 3.2 Basin B (sub-basins 3, 6, & 7) 5 Sub-basin 3 6 Sub-basin 6 6 Sub-basin 7 7 3.3 Basin C (sub-basin 4) 7 3.4 Basin D (sub-basin 5) 8 4.0 Peak Flow Methodology 8 5.0 Water Quality Methodology 9 6.0 Maintenance 10 6.1 Grass Buffer Maintenance 10 6.2 Pervious Pavers 11 6.3 Sump and Pump 11 6.4 Rain Garden 12 6.5 Green Roof 12 7.0 Conclusion 13 LIST OF APPENDICES Appendix A – Proposed Drainage Routing Schematic Appendix B – Tree Canopy Credit Map Appendix C – Water Quality Capture Volume Calculations Appendix D – Peak Flow Calculations – Proposed Conditions 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design 3 1.0 Existing Site 1.1 Description of Existing Site The physical address of the project is 533 W. Hallam Street, Aspen, Colorado and it is located on parcel no. 2735-124-32-001. This parcel is approximately 0.14 acres and is owned by Duncan Skihaus LLC. Current zoning of the property is medium-density residential (R-6). The existing structures on the parcel are one house and a small shed. The project focuses on renovating the house while preserving the historic portion of it. The existing house is 1897 square feet and has two stories with a garage located near the Block 29 alley. 1.2 Description of Existing Drainage Existing storm water runs off several areas of the existing house either as sheet flow or through gutters and downspouts. On the west and north sides of the site, runoff sheet flows over grass to the curb and gutters along W. Hallam & 5th Streets, respectively. Runoff on the east side of the building currently enters the neighboring property. Storm water on the south side of the property enters the alley. No existing storm water detention or treatment BMPs have been found on the site. A soils report was performed for the site by HP Kumar on June 19, 2018. The results found the soil to be Type B with a moderate infiltration rate of 2 to 3 minutes per inch. There is no existing offsite runoff that enters the property. The property exists within the Aspen Mountain Drainage Basin and will not require detention beyond the water quality capture volume (WQCV). Existing peak flow calculations have not been provided for this report because detention will not be required, and runoff will not cross any other properties before discharging to the City of Aspen (COA) storm sewer system. 2.0 Proposed Project The primary purpose of this project is to demolish the non-historic portion of the existing house and build a new addition. Other improvements include the addition of onsite snowmelt pavement and improving storm water runoff quality. The proposed project is considered a major project as defined by the COA Urban Runoff Management Plan (URMP) because more than 1000 square feet and 25% of the site will be disturbed. The proposed residential development with have a footprint of 3160 square feet. The historical portion of the property, which has a footprint of 900 square feet, will be moved north but will remain intact. The main building will be located on the southern portion of the lot with a footprint of 2260 square feet. Storm water quality improvements consist of 1044 square feet of grass buffer, 278.5 square feet of no-infiltration pervious gravel and 6.5 cubic feet of rain gardens. The grass buffer will be located on the western and northern portion of the lot. The no-infiltration pervious gravel will be located on the eastern central portion of the lot. A rain garden is located on the northeast portion of the lot. No storm water generated on the site will flow across the eastern 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design 4 property line onto the neighboring residential lot due to the placement of a curb on the shoring wall extended slightly above grade. Runoff from the eastern side of the lot will flow north to W. Hallam St. through grading. 3.0 Proposed Basins The proposed site has 7 sub-basins, as shown in Appendix A. To clearly describe these sub-basins, they have been grouped into 4 drainage basins based on shared discharge locations and water quality treatment. A summary of the basins can be seen below in Table 1 and detailed calculations for Table 1 can be found in Appendix C. Storm water runoff will be routed to designated BMPs for water quality treatment through a combination of grading and gutters with downspouts. All proposed storm water runoff will discharge from the site as sheet flow to W. Hallam & N. 5th Streets. Basins are detailed in the sections that follow, with tables showing that the required WQCV is treated by BMPs within the basin. The Available WQCV (cf) is calculated as the WQCV provided (in cubic feet) based on grass buffer areas, tree canopy credits, proposed rain garden volume, and pervious gravel sections. Table 1 – Basin Summary 3.1 Basin A (sub-basins 1 & 2) Basin A is located on the north side of the site generally between the property line and the Duncan Skihaus historic building with additional drainage from the front of the historic roof. Sub-basins 1 and 2 comprise Basin A. This basin is 1356 square feet of which 488 square feet is impervious. Tree canopy credit is calculated per section 8.4.1 of the COA URMP, a detailed calculation is shown in Appendix C. A 150 square foot grass buffer and a 6.5 cubic foot rain garden will be used to treat the remaining WQCV. See Appendix A for the proposed location of BMPs in this basin. 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design 5 Table 2 Basin A Basin Area (sf) 1356 % Impervious 36% Required WQCV (cf) 8.39 Credits Green Roof Vol. (cf) 0 Grass Buffer Area (sf) 150 Tree Canopy Credit Area (sf) 190 No-infiltration Paver Vol. (cf) 0 Rain Garden Vol. (cf) 6.5 Results Effective Impervious Area (sf) 148 Effective % Imperviousness 10.9% Net WQCV (cf) -3.1 Available WQCV (cf) 11.5 Sub-basin 1 Sub-basin 1 is located towards north-east corner of the property and has a total and impervious area of 684 and 254 square feet, respectively. This corresponds to 37% impervious area for the sub-basin. This area is mostly a grassed area with the north-eastern portion of the roof included. Storm water will be routed from the roof to a rain garden via roof drainage and gutter downspouts then west to the reverse trench drain and finally, curb and gutter on W. Hallam St. 4” underdrains will be routed to a sump and pump in sub-basin 1. From there the sump and pump will evacuate collected storm water utilizing a reverse trench drain Sub-basin 2 Sub-basin 2 is located at the very north-west corner of the property and has a total and impervious area of 672 and 234 square feet, respectively. This corresponds to 35% impervious area for the sub-basin. This area is mostly a grassed area with the north-western portion of the roof included. Storm water will be routed from the roof to a 150 square foot grass buffer via sheet flow and then north to the curb and gutter on W. Hallam St. Grass buffer is at or above a 1:1 ratio to impervious area, after removing the tree canopy credit. 3.2 Basin B (sub-basins 3, 6, & 7) Basin B is located on the eastern boundary of the site, with a “leg” that reaches the northern boundary of the site and will collect runoff from the back side of the roof of the historic house and the north end of the proposed structure. Sub-basins 3, 6, and 7 comprise Basin B. Storm water runoff will flow from roof areas toward the east property boundary over no- infiltration pervious gravel and then over the front lawn near W. Hallam Street. This basin is 2537 square feet of which 1921 square feet is impervious. No-infiltration pervious gravel, and tree canopy credit will be used to treat the remaining WQCV. The proposed no- infiltration pervious gravel is 315 square feet. See Appendix A for the proposed location of BMPs in this basin. The no-infiltration pervious gravel is based off the no-infiltration pervious 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design 6 paver detail found in figure 8.31 of the COA URMP. Since the landscape architect preferred a gravel surface in this area and the pavers provide no treatment, they are not being used. After water infiltrates through the gravel and enters the underdrain, it is discharged by a reverse trench drain in sub-basin 1 to ensure runoff is leaving the site in the same manner it did historically. Table 3 Basin B Basin Area (sf) 2537 % Impervious 76% Required WQCV (cf) 33.3 Credits Green Roof Vol. (cf) 0 Grass Buffer Area (sf) 0 Tree Canopy Credit Area (sf) 15.6 No-infiltration Paver Vol. (cf) (gravel) 46.4 Rain Garden Vol. (cf) 0 Results Effective Impervious Area (sf) 1905 Effective % Imperviousness 75% Net WQCV (cf) -13.5 Available WQCV (cf) 46.8 Sub-basin 3 Sub-basin 3 is located along the eastern portion of the property, toward W. Hallam Street, and has a total and impervious area of 1262 and 970 square feet, respectively. This corresponds to 66% impervious area for the sub-basin. All storm water in sub-basin 3 will be routed by grading, downspouts and gutters to 126.5 square feet of no-infiltration pervious gravel. Remaining WQCV is treated by tree canopy credits. The no-infiltration pervious gravel in sub-basin 3 result in roughly 4.44 cubic feet of excess available WQCV that can accommodate any untreated runoff from sub-basin 6 (see Section 3.2.2 ). Runoff collected in the hydrodrain hydroduct system for the “green-roof” patios will be directed to an underdrain system and routed to a sump and pump in the crawlspace. This sump and pump will push water to a drain outlet in sub-basin 3 upon which it will hit a splash block and distribute the flow over Mexican beach pebble landscaping of sub-basin 3. Sub-basin 6 Sub-basin 6 is located on the east-central portion of the property and has a total and impervious area of 442 and 327 square feet, respectively. This corresponds to 74% impervious area for the sub-basin. All storm water in sub-basin 6 will be routed by grading, downspouts and gutters to 112.2 square feet of no-infiltration pervious gravel. This results in roughly 13.1 cubic feet of excess available WQCV that can accommodate untreated runoff from sub-basin 7 (see Section 3.2.3). 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design 7 Sub-basin 7 Sub-basin 7 is located on the southern portion of the property and extends from the western most extent to the eastern. Sub-basin 7 has a total and impervious area of 834 and 624 square feet, respectively. This corresponds to 75% impervious area for the sub-basin. This sub-basin is adjacent to the alley along the southern property boundary and has a garage. Runoff generated will not be conveyed through the alley, except for the concrete garage apron. The concrete garage apron will have a micropile wall below and will not accommodate an underdrain to route water towards the rain garden in sub-basin 1. Additionally, the utilities entering from the southeast corner would pose a conflict for the underdrain routing. The remaining runoff from sub-basin 7 will be routed by grading, downspouts and gutters to 39.8 square feet of no-infiltration pervious gravel to the east of the residence. Drainage and grading will allow roughly 4.01 cubic feet of untreated runoff in this basin will sheet flow into sub-basin 6, where there is excess available treatment volume provided by the no-infiltration pervious gravel. 3.3 Basin C (sub-basin 4) Basin C is located on the north-west side of the site and will collect runoff from the back side of the roof for the historic building and the north end of the proposed structure. Basin C consists only of sub-basins 4. Storm water will be routed from both roofed areas across the paver patio and directed to the grass buffers and then sheet flow to 5th Street. The paver patio will be counted as a green roof since the spacing between the pavers will be grass strips. Grass strips contributing to the green roof make up roughly 20% of the surface. The sand composition of the growing substrate is required to be 35% in order to achieve necessary treatment for the roof runoff. Runoff from non-pervious landscaping will sheet flow to the curb and gutter on 5th St. This basin is 796 square feet of which 539 square feet is impervious. Storm water runoff will be treated with 231 square feet of green roof. Remaining WQCV is expected to be treated by the reduction in impervious area provided by a 135.3 square foot tree canopy credit and 257 square feet of grass buffer. Grass buffer is at or above a 1:1 ratio to impervious area, after removing the tree canopy credit and green roof credit. See Appendix A for the proposed location of BMPs in this basin. Water runoff is leaving the site in the same manner it did historically. Table 4 Basin C Basin Area (sf) 796 % Impervious 68% Required WQCV (cf) 9.0 Credits Green Roof Vol. (cf) 3.31 Grass Buffer Area (sf) 257 Tree Canopy Credit Area (sf) 135.3 No-infiltration Paver Vol. (cf) 0.0 Rain Garden Vol. (cf) 0.0 Results Effective Impervious Area (sf) 147 Effective % Imperviousness 18% 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design 8 Net WQCV (cf) -0.3 Available WQCV (cf) 9.3 3.4 Basin D (sub-basin 5) Basin D is located along the west-central portion of the site, comprised solely of sub-basin 5. Storm water will be routed from the roof to pervious pavers and then sheet flow to 5th Street. The paver patio will be counted as a green roof since the spacing between the pavers will be grass strips. Grass strips contributing to the green roof make up roughly 20% of the surface. The sand composition of the growing substrate is required to be 35% in order to achieve necessary treatment for the roof runoff. Runoff from non-pervious landscaping will sheet flow to the curb and gutter on 5th St. This basin is 1312 square feet of which 882 square feet is impervious Storm water runoff will be treated with 293 square feet of green roof. Remaining WQCV is treated by the reduction in effective impervious area provided by the 129 square foot tree canopy credit and 637 square feet of grass buffer area. Grass buffer is at or above a 1:1 ratio to impervious area, after removing the tree canopy credit and green roof credit. See Appendix A for the proposed location of BMPs in this basin. Water runoff is leaving the site in the same manner it did historically. Table 5 Basin D Basin Area (sf) 1312 % Impervious 67% Required WQCV (cf) 14.7 Credits Green Roof Vol. (cf) 4.20 Grass Buffer Area (sf) 637 Tree Canopy Credit Area (sf) 129 No-infiltration Paver Vol. (cf) 0.0 Rain Garden Vol. (cf) 0.0 Results Effective Impervious Area (sf) 116 Effective % Imperviousness 9% Net WQCV (cf) -1.4 Available WQCV (cf) 16.1 4.0 Peak Flow Methodology Proposed drainage flow rates were determined using the rational method as explained in section 3.4 of the URMP and rainfall characteristics as explained in section 2 of the URMP. The rational method calculations for peak flow can be seen in Appendix D. The following tables list the parameters that were used, and the results determined for proposed conditions. 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design 9 Table 6 Watershed Characteristics Imperviousness Overland Flow Time (min) Channel Flow Time (min) Time of Concentration (min) Max Watershed Length (ft) Watershed Slope (ft/ft) C5 63.9% N/A N/A 7.53 100 0.026 0.53 Table 7 Proposed Conditions for 10-Year Storm C10 – Hydro Soil Group B I10 (in/hr) A - (acres) Contributing Area Q10 (cfs) 0.57 3.36 0.14 0.27 Table 8 Proposed Conditions for 100-Year Storm C100 – Hydro Soil Group B I100 (in/hr) A - (acres) Contributing Area Q100 (cfs) 0.73 5.37 0.14 0.54 For the calculation of proposed peak flows, the entire property was modeled as one catchment. This assumption is justified by the relatively small area of the property (the Rational Method is valid to 90 acres and this property is 0.14 acres). From Figure 3.1 of the URMP, the soil can be classified as NRCS Hydrologic Soil Group B. The intensity for the 10- year and 100-year storm were determined using Equation 2-1 of the URMP. 5.0 Water Quality Methodology The Required WQCV (cf) for each basin on the property was estimated from Figure 8.13 of the URMP based on the basin imperviousness and basin area. Then WQCV credits were estimated based on the proposed areas for grass buffers, pervious pavers, and preserved tree canopy (see further discussion of tree canopy credit below). All credits were deducted from the impervious area of the basin and the effective impervious area were computed, based on the instruction of section 8.4.1 in the URMP. From effective impervious area, the effective imperviousness was calculated and an Effective WQCV (cf) was estimated from Figure 8.13. Rain gardens and no-infiltration gravel (porosity = 0.333) were assumed 0.5 ft deep and their capture volumes were deducted from the Effective WQCV (cf) to find the Net WQCV (cf). If Net WQCV (cf) was found to be negative, it implies there is surplus treatment capacity in the basin, and a positive Net WQCV (cf) implies there is a shortage of treatment capacity in the basin. The Available WQCV is defined in this report to be the difference between the Required WQCV (cf) and the Net WQCV (cf). If Available WQCV (cf) is greater than the Required WQCV (cf), this implies there is a surplus treatment capacity within the basin, and if Available WQCV (cf) is less than the Required WQCV (cf), this implies a shortage of treatment within the basin. The Tree Canopy Credit was calculated following the recommendations in section 8.4.1 of the URMP. Detailed calculations for the Tree Canopy Credit can be found in Appendix C. In addition, a map showing the designated trees and their canopy areas is shown in Appendix B. Runoff from all impervious areas will be treated by directing the runoff over a grass buffer, no-infiltration pavers (gravel), green roof, and a rain garden. All proposed runoff will leave the property as sheet flow and will flow over grass lawn located in the right of way before entering the curb and gutter system. 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design 10 6.0 Maintenance 6.1 Grass Buffer Maintenance The following maintenance recommendations were found in the City of Aspen URMP. Mowing recommendations for grass buffers that are included in the Urban Drainage Flood Control District USDCM: Volume 3 Stormwater Quality are provided in the figure below. 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design 11 6.2 Pervious Pavers The following maintenance recommendations were found in the Urban Drainage Flood Control District USDCM: Volume 3 Storm water Quality (page 6-15 to 6-17) and will be used as a guide for the maintenance of the proposed pervious pavers. An inspection of the condition and observation of infiltration should be completed annually. The pavers will lose infiltration capabilities over time and it is recommended to use ASTM C1707 Standard Test Method for Infiltration Rate of In Place Pervious Concrete to measure the infiltration rate of the pavers. A regenerative air or vacuumed sweeper should be used twice annually and after any significant site work, like landscaping, is done. However, the timing of vacuum sweeping is variable based on site conditions and biannual vacuuming may be more often than needed. Sand should never be applied to the pavers for snow removal as this will decrease the permeability of the pavers. The proposed pavers will have snowmelt capabilities, but if snow removal is necessary, mechanical snow removal should be done. If the surface of the paver system ever becomes completely clogged, remove and replacement of the first ½ to 1 inch of infill. The use of a push broom is recommended for the replacement of infill. 6.3 Sump and Pump Sump and pump must be inspected and maintained yearly to remove sediment and debris that is washed into them. Minimum inspection and maintenance requirements include the following: 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design 12 • Inspect sump and pump annually and after every storm exceeding 0.5 inches. • Locate sump lid and cut an outline in sod to replace sod patch after maintenance. • Remove the pump from the sump and clean it and inspect it. • Dispose of sediment, debris/trash, and any other waste material removed from sump at suitable disposal sites and in compliance with local, state, and federal waste regulations. • Check the owner’s manual to see if the pump bearings require grease or oil. If you do not have the manual, look it up on the internet using the manufacturer and model number of your pump or contact the manufacturer. • Replace the pump in the sump and check that it is connected to power. • Dump a bucket of water into the sump to raise the float and make sure the pump turns on, adjusting the float if required. 6.4 Rain Garden The rain garden is to be filled above the filter material with Mexican beach pebbles on the south and long fibered mulch to the north. These filler materials were chosen to integrate with the surrounding landscaping materials and to provide free drainage for the rain garden filter materials below. Annual inspection of the beach pebbles and mulch should be taken to ensure that the material is not clogged and inhibiting drainage. Inspection after large storms should also be taken to ensure that the rain garden is draining as it should. Replacement and/or cleaning of the material should be performed when it is observed that the rain garden is performing less than optimally in its existing condition. 6.5 Green Roof 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design 13 7.0 Conclusion The proposed BMPs (grass buffer, green roof, no-infiltration pervious gravel, and rain gardens) are expected to treat 100% of the required WQCV at the 533 W. Hallam Street project with room to spare. With proper maintenance and installation, these BMPs will meet the criteria outlined in the City of Aspen’s current Urban Runoff Management Plan. 02/28/2020 7 (B) 834 10.76 Sub-basin (Basin) Area WQCV sqft cuft 5 (D) 1312 11.69 6 (B) 442 5.60 3 (B) 1262 16.93 2 (A) 672 4.05 1 (A) 684 4.33 4 (C) 796 4.56 Title: Basins & WQCV Re v i s i o n # Dwg No. Du n c a n S k i h a u s Ci t y o f A s p e n , C o l o r a d o Job No. Drawn by: Date: File: PE:QC: 2018-292.001 JAK 02.06.2020 RB Dun-MajDrRep RB 11 8 W e s t S i x t h S t r e e t , S u i t e 2 0 0 Gl e n w o o d S p r i n g s , C O 8 1 6 0 1 97 0 . 9 4 5 . 1 0 0 4 w w w . s g m - i n c . c o m Da t e By : Pr o j e c t M i l e s t o n e : APPENDIX A 2Of : Graphic Scale In Feet: 1" = 10' 0 5 10 20 02/28/2020 7 (B) 834 10.76 Sub-basin (Basin) Area WQCV sqft cuft 5 (D) 1312 11.69 6 (B) 442 5.60 3 (B) 1262 16.93 2 (A) 672 4.05 1 (A) 684 4.33 4 (C) 796 4.56 Title: Tree Canopy Credit Re v i s i o n # Dwg No. Du n c a n S k i h a u s Ci t y o f A s p e n , C o l o r a d o Job No. Drawn by: Date: File: PE:QC: 2018-292.001 JAK 02.06.2020 RB Dun-MajDrRep RB 11 8 W e s t S i x t h S t r e e t , S u i t e 2 0 0 Gl e n w o o d S p r i n g s , C O 8 1 6 0 1 97 0 . 9 4 5 . 1 0 0 4 w w w . s g m - i n c . c o m Da t e By : -- - - Pr o j e c t M i l e s t o n e : APPENDIX B 2Of : Graphic Scale In Feet: 1" = 10' 0 5 10 20 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design Appendix Appendix C Water Quality Capture Volume Calculations Basin A 𝑷𝒂𝒍𝒂𝒂𝒍𝒍 𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍𝒍𝒂𝒍𝒍=𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍 𝑨𝒍𝒂𝒂 𝑷𝒍𝒍𝒂𝒍 𝑨𝒍𝒂𝒂× 𝟎𝟎𝟎=𝟎𝟎𝟎 𝒂𝒍𝟎 𝟎𝟎𝟎𝟎 𝒂𝒍𝟎× 𝟎𝟎𝟎=𝟎𝟎% Then lookup Required WQCV from Figure 8.13, which is 𝟎.𝟎𝟎𝟎 𝒉𝒍 𝒂𝒂𝒍𝒍𝒉 and… 𝑷𝒂𝒍𝒍𝒉𝒍𝒂𝒂 𝑽𝑷𝑨𝑽 (𝒍𝒍𝒍.)=𝟎.𝟎𝟎𝟎 𝒉𝒍 (𝟎 𝒂𝒍 𝟎𝟎 𝒉𝒍)× 𝑨𝒂𝒍𝒉𝒍 𝑨𝒍𝒂𝒂 =𝟎.𝟎𝟎𝟎 𝒉𝒍 (𝟎 𝒂𝒍 𝟎𝟎 𝒉𝒍)(𝟎𝟎𝟎𝟎 𝒂𝒍𝟎) =𝟎.𝟎𝟎 𝒂𝒍𝟎 Now, find the effective impervious area (𝑬𝑰𝑨)… 𝐴𝐼𝐴 = 𝐼𝑙𝑙𝑐𝑙𝑙.𝐴𝑙𝑐𝑎−𝑃𝑙𝑐𝑐 𝐴𝑎𝑙𝑙𝑙𝑦 𝐴𝑙𝑐𝑐�ℎ𝑙−𝐺𝑙𝑎𝑙𝑙 𝐴𝑙𝑐𝑐𝑐𝑙 𝐴𝑙𝑐𝑎−2(𝑃𝑐𝑙𝑙.𝑃𝑎𝑙𝑐𝑙 𝐴𝑙𝑐𝑎) where… 𝐼𝑙𝑙𝑐𝑙𝑙�ℎ𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=488 𝑐𝑙2 𝐺𝑙𝑎𝑙𝑙 𝐴𝑙𝑐𝑐𝑐𝑙 𝐴𝑙𝑐𝑎=150 𝑐𝑙2 𝑃𝑐𝑙𝑙�ℎ𝑙𝑙𝑙 𝑃𝑎𝑙𝑐𝑙 𝐴𝑙𝑐𝑎=0 𝑐𝑙2 and… 𝑃𝑙𝑐𝑐 𝐴𝑎𝑙𝑙𝑙𝑦 𝐴𝑙𝑐𝑐�ℎ𝑙=0.15(𝐴𝑐𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎)+0.3(𝐴𝑙𝑙𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎) where… 𝐴𝑐𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=309 𝑐𝑙2 𝐴𝑙𝑙�ℎ𝑐𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=478 𝑐𝑙2 so… 𝐴𝐼𝐴=480 𝑐𝑙2 −0.15(309 𝑐𝑙2)−0.3(478 𝑐𝑙2)−150 𝑐𝑙2 𝐴𝐼𝐴= 148 𝑐𝑙2 and… 𝑬𝒂𝒂.𝑷𝒂𝒍𝒂𝒂𝒍𝒍 𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍𝒍𝒂𝒍𝒍=𝟎𝟎.𝟎% Then use it to find Effective WQCV from Figure 8.13, which is 𝟎.𝟎𝟎𝟎 𝒉𝒍 𝒂𝒂𝒍𝒍𝒉 and… 𝐴𝑐𝑐𝑐𝑐𝑙�ℎ𝑙𝑐 𝑉𝑃𝐴𝑉 (𝑐𝑙3)=0.030 �ℎ𝑙(1 𝑐𝑙 12 �ℎ𝑙)× 𝐴𝑎𝑙�ℎ𝑙 𝐴𝑙𝑐𝑎 = 0.030 �ℎ𝑙 (1 𝑐𝑙 12 �ℎ𝑙)(1356 𝑐𝑙2) =3.39 𝑐𝑙3 𝐿𝑙 𝐼𝑙𝑐�ℎ𝑙𝑙𝑙𝑎𝑙�ℎ𝑙𝑙 𝑃𝑐𝑙𝑙.𝑃𝑎𝑙𝑐𝑙 𝑉𝑙𝑙𝑙𝑙𝑐=𝐴𝑙𝑐𝑎× 𝑐𝑐𝑙𝑙�× 𝑃𝑐𝑙𝑐𝑐𝑙𝑙 𝑉𝑙�ℎ𝑐 𝑃𝑙𝑎𝑐𝑐 =(0 𝑐𝑙2)(𝐿�ℎ𝑙.0.5 𝑐𝑙 𝑐𝑐𝑙𝑙�)(33%) =0 𝑐𝑙3 𝑃𝑎�ℎ𝑙 𝐺𝑎𝑙𝑐𝑐𝑙 𝑉𝑙𝑙𝑙𝑙𝑐=6.50 𝑐𝑙3 Finally… 𝑵𝒂𝒍 𝑽𝑷𝑨𝑽=(𝐴𝑐𝑐𝑐𝑐𝑙�ℎ𝑙𝑐 𝑉𝑃𝐴𝑉)−(𝐿𝑙−𝐼𝑙𝑐�ℎ𝑙𝑙𝑙𝑎𝑙�ℎ𝑙𝑙 𝑃𝑐𝑙𝑙.𝑃𝑎𝑙𝑐𝑙 𝑉𝑙𝑙.)−𝑃𝑎�ℎ𝑙 𝐺𝑎𝑙𝑐𝑐𝑙 𝑉𝑙𝑙. =3.39 𝑐𝑙3 −0 𝑐𝑙3 −6.5 𝑐𝑙3 𝑵𝒂𝒍 𝑽𝑷𝑨𝑽=−𝟎.𝟎 𝒂𝒍𝟎 𝑨𝒍𝒂𝒉𝒍𝒂𝒂𝒍𝒂 𝑽𝑷𝑨𝑽=𝑃𝑐𝑙𝑙�ℎ𝑙𝑐𝑐 𝑉𝑃𝐴𝑉−𝐿𝑐𝑙 𝑉𝑃𝐴𝑉 = 𝟎𝟎.𝟎 𝒂𝒍𝟎 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design Appendix Basin B 𝑷𝒂𝒍𝒂𝒂𝒍𝒍 𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍𝒍𝒂𝒍𝒍=𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍 𝑨𝒍𝒂𝒂 𝑷𝒍𝒍𝒂𝒍 𝑨𝒍𝒂𝒂× 𝟎𝟎𝟎=𝟎𝟎𝟎𝟎 𝒂𝒍𝟎 𝟎𝟎𝟎𝟎 𝒂𝒍𝟎× 𝟎𝟎𝟎=𝟎𝟎% Then lookup Required WQCV from Figure 8.13, which is 𝟎.𝟎𝟎𝟎 𝒉𝒍 𝒂𝒂𝒍𝒍𝒉 and… 𝑷𝒂𝒍𝒍𝒉𝒍𝒂𝒂 𝑽𝑷𝑨𝑽 (𝒍𝒍𝒍.)=𝟎.𝟎𝟎𝟎 𝒉𝒍 (𝟎 𝒂𝒍 𝟎𝟎 𝒉𝒍)× 𝑨𝒂𝒍𝒉𝒍 𝑨𝒍𝒂𝒂 =𝟎.𝟎𝟎𝟎 𝒉𝒍 (𝟎 𝒂𝒍 𝟎𝟎 𝒉𝒍)(𝟎𝟎𝟎𝟎 𝒂𝒍𝟎) =𝟎𝟎.𝟎𝟎 𝒂𝒍𝟎 Now, find the effective impervious area (𝑬𝑰𝑨)… 𝐴𝐼𝐴 = 𝐼𝑙𝑙𝑐𝑙𝑙.𝐴𝑙𝑐𝑎−𝑃𝑙𝑐𝑐 𝐴𝑎𝑙𝑙𝑙𝑦 𝐴𝑙𝑐𝑐�ℎ𝑙−𝐺𝑙𝑎𝑙𝑙 𝐴𝑙𝑐𝑐𝑐𝑙 𝐴𝑙𝑐𝑎−2(𝑃𝑐𝑙𝑙.𝑃𝑎𝑙𝑐𝑙 𝐴𝑙𝑐𝑎) where… 𝐼𝑙𝑙𝑐𝑙𝑙�ℎ𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=1921 𝑐𝑙2 𝐺𝑙𝑎𝑙𝑙 𝐴𝑙𝑐𝑐𝑐𝑙 𝐴𝑙𝑐𝑎=0 𝑐𝑙2 𝑃𝑐𝑙𝑙�ℎ𝑙𝑙𝑙 𝑃𝑎𝑙𝑐𝑙 𝐴𝑙𝑐𝑎=0 𝑐𝑙2 and… 𝑃𝑙𝑐𝑐 𝐴𝑎𝑙𝑙𝑙𝑦 𝐴𝑙𝑐𝑐�ℎ𝑙=0.15(𝐴𝑐𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎)+0.3(𝐴𝑙𝑙𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎) where… 𝐴𝑐𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=104 𝑐𝑙2 𝐴𝑙𝑙�ℎ𝑐𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=0 𝑐𝑙2 so… 𝐴𝐼𝐴=1921 𝑐𝑙2 −0.15(104 𝑐𝑙2)−0.3(0 𝑐𝑙2)−0 𝑐𝑙2 𝐴𝐼𝐴= 1905 𝑐𝑙2 and… 𝑬𝒂𝒂.𝑷𝒂𝒍𝒂𝒂𝒍𝒍 𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍𝒍𝒂𝒍𝒍=𝟎𝟎% Then use it to find Effective WQCV from Figure 8.13, which is 𝟎.𝟎𝟎𝟎 𝒉𝒍 𝒂𝒂𝒍𝒍𝒉 and… 𝑬𝒂𝒂𝒂𝒂𝒍𝒉𝒍𝒂 𝑽𝑷𝑨𝑽 (𝒂𝒍𝟎)=0.156 �ℎ𝑙(1 𝑐𝑙 12 �ℎ𝑙)× 𝐴𝑎𝑙�ℎ𝑙 𝐴𝑙𝑐𝑎 = 0.156 �ℎ𝑙 (1 𝑐𝑙 12 �ℎ𝑙)(2537 𝑐𝑙2) =32.9 𝑐𝑙3 𝐿𝑙𝐼𝑙𝑐�ℎ𝑙𝑙𝑙𝑎𝑙�ℎ𝑙𝑙 𝑃𝑐𝑙𝑙.𝑃𝑎𝑙𝑐𝑙 𝑉𝑙𝑙𝑙𝑙𝑐=𝐴𝑙𝑐𝑎× 𝑐𝑐𝑙𝑙�× 𝑃𝑐𝑙𝑐𝑐𝑙𝑙 𝑉𝑙�ℎ𝑐 𝑃𝑙𝑎𝑐𝑐 =(278 𝑐𝑙2)(0.5 𝑐𝑙 𝑐𝑐𝑙𝑙�)(33%) =46.4 𝑐𝑙3 𝑃𝑎�ℎ𝑙 𝐺𝑎𝑙𝑐𝑐𝑙 𝑉𝑙𝑙𝑙𝑙𝑐=0 𝑐𝑙3 Finally… 𝑵𝒂𝒍 𝑽𝑷𝑨𝑽=(𝐴𝑐𝑐𝑐𝑐𝑙�ℎ𝑙𝑐 𝑉𝑃𝐴𝑉)−(𝐿𝑙−𝐼𝑙𝑐�ℎ𝑙𝑙𝑙𝑎𝑙�ℎ𝑙𝑙 𝑃𝑐𝑙𝑙.𝑃𝑎𝑙𝑐𝑙 𝑉𝑙𝑙.)−𝑃𝑎�ℎ𝑙 𝐺𝑎𝑙𝑐𝑐𝑙 𝑉𝑙𝑙. =32.9 𝑐𝑙3 −46.4 𝑐𝑙3 −0 𝑐𝑙3 𝑷𝒍𝒂𝒂𝒍𝒂𝒂 𝑽𝑷𝑨𝑽=−𝟎𝟎.𝟎 𝒂𝒍𝟎 𝑨𝒍𝒂𝒉𝒍𝒂𝒂𝒍𝒂 𝑽𝑷𝑨𝑽=𝑃𝑐𝑙𝑙�ℎ𝑙𝑐𝑐 𝑉𝑃𝐴𝑉−𝐿𝑐𝑙 𝑉𝑃𝐴𝑉 = 𝟎𝟎.𝟎 𝒂𝒍𝟎 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design Appendix Basin C 𝑷𝒂𝒍𝒂𝒂𝒍𝒍 𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍𝒍𝒂𝒍𝒍=𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍 𝑨𝒍𝒂𝒂 𝑷𝒍𝒍𝒂𝒍 𝑨𝒍𝒂𝒂× 𝟎𝟎𝟎=𝟎𝟎𝟎 𝒂𝒍𝟎 𝟎𝟎𝟎 𝒂𝒍𝟎× 𝟎𝟎𝟎=𝟎𝟎% Then lookup Required WQCV from Figure 8.13, which is 𝟎.𝟎𝟎𝟎 𝒉𝒍 𝒂𝒂𝒍𝒍𝒉 and… 𝑷𝒂𝒍𝒍𝒉𝒍𝒂𝒂 𝑽𝑷𝑨𝑽 (𝒍𝒍𝒍.)=𝟎.𝟎𝟎𝟎 𝒉𝒍 (𝟎 𝒂𝒍 𝟎𝟎 𝒉𝒍)× 𝑨𝒂𝒍𝒉𝒍 𝑨𝒍𝒂𝒂 =𝟎.𝟎𝟎𝟎 𝒉𝒍 (𝟎 𝒂𝒍 𝟎𝟎 𝒉𝒍)(𝟎𝟎𝟎 𝒂𝒍𝟎) =𝟎.𝟎 𝒂𝒍𝟎 Now, find the effective impervious area (𝑬𝑰𝑨)… 𝐴𝐼𝐴 = 𝐼𝑙𝑙𝑐𝑙𝑙.𝐴𝑙𝑐𝑎−𝑃𝑙𝑐𝑐 𝐴𝑎𝑙𝑙𝑙𝑦 𝐴𝑙𝑐𝑐�ℎ𝑙−𝐺𝑙𝑎𝑙𝑙 𝐴𝑙𝑐𝑐𝑐𝑙 𝐴𝑙𝑐𝑎 where… 𝐼𝑙𝑙𝑐𝑙𝑙�ℎ𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=539 𝑐𝑙2 𝐺𝑙𝑎𝑙𝑙 𝐴𝑙𝑐𝑐𝑐𝑙 𝐴𝑙𝑐𝑎=257 𝑐𝑙2 and… 𝑃𝑙𝑐𝑐 𝐴𝑎𝑙𝑙𝑙𝑦 𝐴𝑙𝑐𝑐�ℎ𝑙=0.15(𝐴𝑐𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎)+0.3(𝐴𝑙𝑙𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎) where… 𝐴𝑐𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=51 𝑐𝑙2 𝐴𝑙𝑙�ℎ𝑐𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=425 𝑐𝑙2 so… 𝐴𝑐𝑐.𝐼𝑙𝑙.𝐴𝑙𝑐𝑎=756 𝑐𝑙2 −0.15(51 𝑐𝑙2)−0.3(425 𝑐𝑙2)−257 𝑐𝑙2 𝐴𝑐𝑐.𝐼𝑙𝑙.𝐴𝑙𝑐𝑎= 147 𝑐𝑙2 and… 𝑬𝒂𝒂.𝑷𝒂𝒍𝒂𝒂𝒍𝒍 𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍𝒍𝒂𝒍𝒍=𝟎𝟎% 𝐺𝑙𝑐𝑐𝑙 𝑃𝑙𝑙𝑐 𝑉𝑙𝑙𝑙𝑙𝑐=3.31 𝑐𝑙3 𝐿𝑙𝐼𝑙𝑐�ℎ𝑙𝑙𝑙𝑎𝑙�ℎ𝑙𝑙 𝑃𝑐𝑙𝑙.𝑃𝑎𝑙𝑐𝑙 𝑉𝑙𝑙𝑙𝑙𝑐=0 𝑐𝑙3 𝑃𝑎�ℎ𝑙 𝐺𝑎𝑙𝑐𝑐𝑙 𝑉𝑙𝑙𝑙𝑙𝑐=0 𝑐𝑙3 Finally… 𝑵𝒂𝒍 𝑽𝑷𝑨𝑽=(𝐴𝑐𝑐𝑐𝑐𝑙�ℎ𝑙𝑐 𝑉𝑃𝐴𝑉)−𝐺𝑙𝑐𝑐𝑙 𝑃𝑙𝑙𝑐 𝑉𝑙𝑙𝑙𝑙𝑐− (𝐿𝑙−𝐼𝑙𝑐�ℎ𝑙𝑙𝑙𝑎𝑙�ℎ𝑙𝑙 𝑃𝑐𝑙𝑙.𝑃𝑎𝑙𝑐𝑙 𝑉𝑙𝑙.) −𝑃𝑎�ℎ𝑙 𝐺𝑎𝑙𝑐𝑐𝑙 𝑉𝑙𝑙. =3.0 𝑐𝑙3 −3.3 𝑐𝑙3 −0 𝑐𝑙3 −0 𝑐𝑙3 𝑷𝒍𝒂𝒂𝒍𝒂𝒂 𝑽𝑷𝑨𝑽=𝟎.𝟎 𝒂𝒍𝟎 𝑨𝒍𝒂𝒉𝒍𝒂𝒂𝒍𝒂 𝑽𝑷𝑨𝑽=𝑃𝑐𝑙𝑙�ℎ𝑙𝑐𝑐 𝑉𝑃𝐴𝑉−𝐿𝑐𝑙 𝑉𝑃𝐴𝑉 = 𝟎.𝟎 𝒂𝒍𝟎 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design Appendix Basin D 𝑷𝒂𝒍𝒂𝒂𝒍𝒍 𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍𝒍𝒂𝒍𝒍=𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍 𝑨𝒍𝒂𝒂 𝑷𝒍𝒍𝒂𝒍 𝑨𝒍𝒂𝒂× 𝟎𝟎𝟎=𝟎𝟎𝟎 𝒂𝒍𝟎 𝟎𝟎𝟎𝟎 𝒂𝒍𝟎× 𝟎𝟎𝟎=𝟎𝟎% Then lookup Required WQCV from Figure 8.13, which is 𝟎.𝟎𝟎𝟎 𝒉𝒍 𝒂𝒂𝒍𝒍𝒉 and… 𝑷𝒂𝒍𝒍𝒉𝒍𝒂𝒂 𝑽𝑷𝑨𝑽 (𝒍𝒍𝒍.)=𝟎.𝟎𝟎𝟎 𝒉𝒍 (𝟎 𝒂𝒍 𝟎𝟎 𝒉𝒍)× 𝑨𝒂𝒍𝒉𝒍 𝑨𝒍𝒂𝒂 =𝟎.𝟎𝟎𝟎 𝒉𝒍 (𝟎 𝒂𝒍 𝟎𝟎 𝒉𝒍)(𝟎𝟎𝟎𝟎 𝒂𝒍𝟎) =𝟎𝟎.𝟎 𝒂𝒍𝟎 Now, find the effective impervious area (𝑬𝑰𝑨)… 𝐴𝐼𝐴 = 𝐼𝑙𝑙𝑐𝑙𝑙.𝐴𝑙𝑐𝑎−𝑃𝑙𝑐𝑐 𝐴𝑎𝑙𝑙𝑙𝑦 𝐴𝑙𝑐𝑐�ℎ𝑙−𝐺𝑙𝑎𝑙𝑙 𝐴𝑙𝑐𝑐𝑐𝑙 𝐴𝑙𝑐𝑎 where… 𝐼𝑙𝑙𝑐𝑙𝑙�ℎ𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=882 𝑐𝑙2 𝐺𝑙𝑎𝑙𝑙 𝐴𝑙𝑐𝑐𝑐𝑙 𝐴𝑙𝑐𝑎=637 𝑐𝑙2 and… 𝑃𝑙𝑐𝑐 𝐴𝑎𝑙𝑙𝑙𝑦 𝐴𝑙𝑐𝑐�ℎ𝑙=0.15(𝐴𝑐𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎)+0.3(𝐴𝑙𝑙𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎) where… 𝐴𝑐𝑐�ℎ𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=858 𝑐𝑙2 𝐴𝑙𝑙�ℎ𝑐𝑐𝑙𝑙𝑙𝑙 𝐴𝑙𝑐𝑎=0 𝑐𝑙2 so… 𝐴𝑐𝑐.𝐼𝑙𝑙.𝐴𝑙𝑐𝑎=882 𝑐𝑙2 −0.15(0 𝑐𝑙2)−0.3(858 𝑐𝑙2)−637 𝑐𝑙2 𝐴𝑐𝑐.𝐼𝑙𝑙.𝐴𝑙𝑐𝑎= 116 𝑐𝑙2 and… 𝑬𝒂𝒂.𝑷𝒂𝒍𝒂𝒂𝒍𝒍 𝑰𝒍𝒍𝒂𝒍𝒍𝒉𝒍𝒍𝒍𝒍𝒂𝒍𝒍=𝟎% 𝐺𝑙𝑐𝑐𝑙 𝑃𝑙𝑙𝑐 𝑉𝑙𝑙𝑙𝑙𝑐=4.2 𝑐𝑙3 𝐿𝑙𝐼𝑙𝑐�ℎ𝑙𝑙𝑙𝑎𝑙�ℎ𝑙𝑙 𝑃𝑐𝑙𝑙.𝑃𝑎𝑙𝑐𝑙 𝑉𝑙𝑙𝑙𝑙𝑐=0 𝑐𝑙3 𝑃𝑎�ℎ𝑙 𝐺𝑎𝑙𝑐𝑐𝑙 𝑉𝑙𝑙𝑙𝑙𝑐=0 𝑐𝑙3 Finally… 𝑵𝒂𝒍 𝑽𝑷𝑨𝑽=(𝐴𝑐𝑐𝑐𝑐𝑙�ℎ𝑙𝑐 𝑉𝑃𝐴𝑉)−𝐺𝑙𝑐𝑐𝑙 𝑃𝑙𝑙𝑐 𝑉𝑙𝑙𝑙𝑙𝑐− (𝐿𝑙−𝐼𝑙𝑐�ℎ𝑙𝑙𝑙𝑎𝑙�ℎ𝑙𝑙 𝑃𝑐𝑙𝑙.𝑃𝑎𝑙𝑐𝑙 𝑉𝑙𝑙.) −𝑃𝑎�ℎ𝑙 𝐺𝑎𝑙𝑐𝑐𝑙 𝑉𝑙𝑙. =2.8 𝑐𝑙3 −4.2 𝑐𝑙3 0 𝑐𝑙3 −0 𝑐𝑙3 𝑷𝒍𝒂𝒂𝒍𝒂𝒂 𝑽𝑷𝑨𝑽=𝟎.𝟎 𝒂𝒍𝟎 𝑨𝒍𝒂𝒉𝒍𝒂𝒂𝒍𝒂 𝑽𝑷𝑨𝑽=𝑃𝑐𝑙𝑙�ℎ𝑙𝑐𝑐 𝑉𝑃𝐴𝑉−𝐿𝑐𝑙 𝑉𝑃𝐴𝑉 = 𝟎𝟎.𝟎 𝒂𝒍𝟎 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design Appendix Appendix D Peak Flow Calculations for Project Site – Proposed Conditions • Watershed Area, 𝐴 𝑨=𝟎𝟎𝟎𝟎 𝒂𝒍𝟎=𝟎.𝟎𝟎 𝒂𝒂𝒍𝒂𝒍 • Percent Imperviousness, �ℎ �ℎ=𝐴𝑖𝑙𝑜 𝐴𝑡𝑜𝑡𝑎𝑙 × 100 �ℎ=488 𝑐𝑙2 +1921 𝑐𝑙2 +539 𝑐𝑙2 +882 𝑐𝑙2 6000 𝑐𝑙2 × 100 𝒉=𝟎𝟎.𝟎 % • Maximum Watershed Length, 𝐿0 𝑳𝟎=𝟎𝟎𝟎 𝒂𝒍,extent of property from South to North • Watershed Slope, 𝑃0 𝑃0 =𝐴𝑙𝑐𝑙𝑎𝑙�ℎ𝑙𝑙 𝑎𝑙 𝑙𝑙𝑙𝑙� 𝑐𝑙𝑐−𝐴𝑙𝑐𝑙𝑎𝑙�ℎ𝑙𝑙 𝑎𝑙 𝑙𝑙𝑙𝑙� 𝑐𝑙𝑐 𝐿0 𝑃0 =7915.14 𝑐𝑙−7912.54 𝑐𝑙 100 𝑐𝑙 𝑷𝟎=𝟎.𝟎× 𝟎𝟎−𝟎 • Runoff Coefficients, 𝐴5, 𝐴10, & 𝐴100 Expressions for the 5-, 10-, and 100-year storm return period runoff coefficients can be found in Table 6-4 in the Urban Drainage and Flood Control District (UDFCD) Urban Storm Drainage Criteria Manual (USDCM) 𝐴5 =0.86�ℎ0.33 =0.5283 𝐴10 =0.81�ℎ+0.057 =0.5746 𝐴100 =0.47�ℎ+0.426 =0.7263 • Computed Time of Concentration, 𝑃𝑐 𝑃𝑐=𝑃𝑜+𝑃𝑓 where… 𝑃𝑜=0.395(1.1−𝐶5√𝐾0) 𝑅00.33 (Overland flow time, Equation 3-4 in COA URMP) 𝑃𝑓=𝐾𝑓 60𝐾√𝑅𝑓 (Channelized flow time, Equation 3-5 in COA URMP) And since there’s no channelized flow, 𝑃𝑓=0 so… 𝑃𝐶=𝑃𝑜=0.395(1.1 −0.5283)√100 𝑐𝑙 (2.6 × 10−2)0.33 𝑷𝑨=𝟎.𝟎𝟎 𝒍𝒉𝒍𝒍𝒍𝒂𝒍 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design Appendix • Design Time of Concentration, 𝑃𝑐 The design time of concentration, 𝑃𝑐, is the lesser of the computed time of concentration, 𝑃𝑐, and the regional time of concentration, 𝑃𝑅, which is given by 𝑃𝑅=10 +𝐿0/180 =10 +(100 𝑐𝑙/180) =10.6 𝑙�ℎ𝑙𝑙𝑙𝑐𝑙 so… 𝑷𝒂=𝟎.𝟎 𝒍𝒉𝒍𝒍𝒍𝒂𝒍 • Peak Runoff for 10-year Storm Return Period, 𝑃10 𝑃10 =𝐴10𝐼10𝐴 where 𝐴10 is the 10-year runoff coefficient, 𝐼10 is the 10-year storm rainfall intensity (units of �ℎ𝑙/�𝑙), and 𝐴 is the watershed area in units of 𝑎𝑐𝑙𝑐𝑙 𝐼10 =88.8𝑃1 (10+𝑅𝑑)1.052 (Equation 2-1 in COA URMP) and 𝑃1 is the 1-hr precipitation intensity for a 10-year storm 𝑃1 =0.77 �ℎ𝑙/�𝑙 (Table 2.2 of the COA URMP) so… 𝐼10 =88.8(0.77) (10 +7.5)1.052 𝑰𝟎𝟎=𝟎.𝟎𝟎𝒉𝒍 𝒉𝒍 then the 10-year peak runoff is given by.. 𝑃10 =(0.5283)(3.36 �ℎ𝑙 �𝑙)(0.14 𝑎𝑐𝑙𝑐𝑙) 𝑷𝟎𝟎=𝟎.𝟎𝟎𝟎 𝒂𝒂𝒍 • Peak Runoff for 100-year Storm Return Period, 𝑃100 𝑃100 =𝐴100𝐼100𝐴 where 𝐴10 is the 100-year runoff coefficient, 𝐼10 is the 100-year storm rainfall intensity (units of �ℎ𝑙/�𝑙), and 𝐴 is the watershed area in units of 𝑎𝑐𝑙𝑐𝑙 𝐼100 =88.8𝑃1 (10+𝑅𝑑)1.052 (Equation 2-1 in COA URMP) and 𝑃1 is the 1-hr precipitation intensity for a 100-year storm 𝑃1 =1.23 �ℎ𝑙/�𝑙 (Table 2.2 of the COA URMP) so… 02/28/2020 533 W. Hallam Street, Aspen, Colorado February 10, 2020 Drainage Report for Major Design Appendix 𝐼100 =88.8(1.23) (10 +7.5)1.052 𝑰𝟎𝟎𝟎=𝟎.𝟎𝟎𝒉𝒍 𝒉𝒍 then the 100-year peak runoff is given by 𝑃100 =(0.7263)(5.37 �ℎ𝑙 �𝑙)(0.14 𝑎𝑐𝑙𝑐𝑙) 𝑷𝟎𝟎𝟎=𝟎.𝟎𝟎𝟎 𝒂𝒂𝒍 02/28/2020