HomeMy WebLinkAboutFile Documents.813 W Smuggler St.0253.2018 (29).ARBK
DRAINAGE REPORT
FOR
RANGER STATION SUBDIVISION
Lot 3
813 West Smuggler
CITY OF ASPEN, COLORADO
PARCEL ID: 2735-124-28-003
PREPARED FOR:
Ranger Station Subdivision
Aspen, CO 81611
PREPARED BY:
High Country Engineering, Inc.
1517 Blake Avenue, Suite 101
Glenwood Springs, CO 81601
(970) 945-8676
March 15, 2019
HCE JOB NUMBER: 2181030.03
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TABLE OF CONTENTS
SECTION PAGE
I. GENERAL LOCATION AND DESCRIPTION OF SITE 4
II. DRAINAGE STUDIES 6
III. EXISTING SUB BASIN DESCRIPTION 6
IV. DRAINAGE DESIGN CRITERIA 7
V. DRAINAGE FACILITY DESIGN 10
VI. CONCLUSION 14
VIII. REFERENCES 15
EXHIBITS:
1. Vicinity Map (8.5”x11”)
2. Flow Path (8.5”x11”)
3. Existing Drainage Basin Map (24”x36”)
4. Proposed Drainage Basin Map (24”x36”)
5. FEMA Mapping (11”x17”)
6. USDA Web Soil Survey (8.5”x11”)
7. HP-Kumar Subsoil Study & Percolation Test for Lot 3 (8.5”x11”)
Appendices
Hydrologic Computations
Existing Conditions
Proposed Conditions
Hydraulic Computations
Swale & Pipe Calculations
Trench Drain
Drywell-Detention
Weir
Aspen Charts and Figures
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Engineers Certification
“I hereby affirm that this report and the accompanying plans for the construction of access
drive improvements at Ranger Station Subdivision, Aspen, CO was prepared by me (or under
my direct supervision) for the owners thereof in accordance with the provisions of the City of
Aspen Urban Runoff Management Plan and approved variances are 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.”
License No. 29975
Roger D. Neal, P.E.
Licensed Professional Engineer, State of Colorado
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I. GENERAL LOCATION AND DESCRIPTION OF SITE
A. Location
Lot 2 of the Ranger Station Subdivision is located in the Castle Creek Drainage Basin. The
property is approximately 800 feet east of Castle Creek and 2,300 feet south of the Roaring
Fork River. A 20’ ditch easement runs within this lot on the easterly side of this property
along a slight rise. North 8th Street is located west of the property separated by lots 1 and 2
of the same subdivision and provides the access via an alley to the garage. North 8th
continues northerly for approximately 600 feet and intersects Meadows road. West Smuggler
bounds the property to the north. The site is located within the City of Aspen, County of
Pitkin, and State of Colorado. A Vicinity Map has been included as Exhibit #1.
B. Description of Property
The proposed Lot 1 also known as 813 W. Smuggler in the Ranger Station Subdivision site is
approximately 6,619 square feet (0.152 acres) in size per the amended and restated plat. The
north and west property lines run parallel to West Smuggler Street and North 8th Street. The
south and east sides of the proposed lot is bound by Lot 4 to the south and Forest Service
Headquarters land to the east. An easement on lots 1-4 create the access to lots 1-4 in a newly
created alley that is currently under construction. The north and south sides are bound by
roadways and vegetation. The east and west sides are bound by lots 2 of Ranger Station
Subdivision and Forest Service Headquarters land on the easterly side separated by a 20’
easement for a COA irrigation ditch that runs on both properties at a slight northeast diagonal.
The existing site consists of vegetation, the irrigation ditch and the alley under construction.
There are no affected trees on the site per the survey conducted by HCE and Sopris
Engineering. The only noted trees are in the ROW of W. Smugger and those existing trees are
not going to be disturbed. The only other remaining trees on the site are within the ditch
easement and are to be protected from the proposed construction activities per the City
Foresters recommendations during construction.
The storm water on the existing site flows from southeast to the northwest. The eastern side of
the site is the irrigation ditch, and stormwater flows will flow to the ditch and then northerly
off site. Southern stormwater flows will be intercepted by the proposed driveway trench
drains and discharged into the vegetated swale of the Lot 3 storm system. Flows from the
west are intercepted by Lot 2 and will be contained within that lot. Stormwater on-site will
flow through the storm-water system on the lot and will discharge northerly into the W.
Smuggler ROW as it has historically. There are four design points that show the location of
historic runoff released on site. These include the alley runoff captured in the driveway, two
discharge points into the pond, the ditch east of the site, and the location of site overflow. The
main historic release for this site is at the northwest corner of the site, and the flows convey
offsite as overflow from a pond and drywell system during major events. The irrigation ditch
also is considered a historic release but only captures storm flows that fall within the easement
or grasses next to the home and no impervious surfaces. This site is located on the boundary
of the Castle Creek and Aspen Mountain drainage basins; therefore, no significant offsite
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basins were used in the design. The historic drainage of the site was delineated into two
basins; see attached existing basin map for site layout (EXDR-01).
C. Lot Soils Description
A site-specific geotechnical soil study was completed for foundation design and percolation
testing has been provided for Lot 3 (Exhibit #7). The site is well above the river elevation and
groundwater was not encountered to approximately the depth of the drywell level. The City of
Aspen soils map locates this site in the Type “B” soils area. According to the USDA Web Soil
Survey, the property is within section 107 and the report states that it consists of soil Type
“B”; see USDA Web Soil Survey (Exhibit #6).
D. Description of Project Goals
The proposed project will consist of construction of a new home and the associated grading,
access utilities and landscaping. The largest portion of the construction will be the
construction of the home including excavation of a deep basement and utilities into the
foundation. Since this is a small lot, much of the site will be disturbed. The only vegetation
on the site to be preserved are the trees near the alley, the vegetation and bushes in the
irrigation easement and trees outside the property to the north in W. Smuggler ROW. Site
landscaping will include grass swales, as well as grasses, trees and shrubs around the home to
the west, north and east to revegetate the disturbed areas of the site. The site is located in the
Castle Creek Basin; therefore, the property owner will not be able to pay the fee-in-lieu of
detention.
The proposed home drainage will be mitigated by providing site detention and water quality
within the site through a stormwater system with a grass-lined swale, bio-retention pond and
drywell. The pond and drywell will collect the required WQCV per the city code at the
required volume. An underdrain allows the pond to drain to the drywell for additional water
quality and detention volume. Stormwater will flow directly into the drywell through an
overflow inlet in the pond. For larger storms that fill the pond and drywell, an overflow weir
will allow flows to follow the historic route once both systems inundate. The drywell and
pond will collect the detention volume and will discharge to groundwater through the drywell
and to W. Smuggler Street for larger storm events through a controlled weir. The pond
provides the controlled release at the northwest corner of the property via a stepped weir. The
site is required to capture 59.7 CF of WQCV. The site is also required to capture 73CF of
detention, thus sizing the drywell and pond to capture a minimum of 348 CF, well in excess
of the calculated requirement, to allow for a factor of safety since there is room to have some
redundancy; see attached WQCV and detention drywell calculations in the Appendices.
The site consists of four proposed basin, see attached proposed basin map for site layout
(Exhibit #4).
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II. DRAINAGE STUDIES
A. Major Basin Description
The proposed site is located on FEMA’s Flood Insurance Rate Map (FIRM) No.
08097C0203C which has an effective date of June 4, 1987. The site is located in Zone-X, this
zone is described as areas determined to be outside 100-year and 500-year floodplains. The
100 year floodway line follows the Roaring Fork River to the west of the site per the survey
documents and FEMA mapping. There is one 20-foot access and utility easement within the
site.
The existing site is outside the affected areas per the WRC Engineering mapping and report
for 100yr and mudflow events. The Mud Flow Zone mapping in the Storm Drainage Master
Plan for the City of Aspen, Colorado by WRC Engineering, Inc. in November of 2001 was
utilized for this section. Other residential areas surround the property.
B. Previous Drainage Studies
There are no previous site specific drainage studies for the site. The proposed site is located
within the Study Area Boundary for the “Storm Drainage Plan for the City of Aspen” by WRC
Engineering, Inc. in November 2001; however, the site does not drain to the storm sewer
system for the City of Aspen.
C. Receiving System and Effects of Adjacent Drainage Issues
There are no major drainage issues with the adjacent properties that affect the site or that the
site affects. The existing site north and east of the site discharges sheet flow to the north and
west property lines as it did historically. The area southwest of the existing site discharges to
an N. 8th roadside swale, then travels north and discharges into the Nth. 8th and W. Smuggler
intersection. From there the road appears to carry the drainage northerly and ultimately
draining through some large parcels and into the castle creek wetlands. The area southeast of
the site discharges northerly along with this site to West Smuggler and down Nth. 8th as
before. This system ultimately delivers the stormwater to Castle Creek then the Roaring Fork
River.
III. EXISTING SUB BASINS DESCRIPTION
The existing site’s historic drainage patterns flow from the southeast to the northwest. As
stated above, Castle Creek and the Roaring Fork River are the direct receiving facilities. The
difference in the historic conditions versus the proposed conditions with historic condition
flowrates will determine the amount of storm water allowed to flow offsite.
The historic site is depicted as two onsite drainage basins. Refer to sheet EXDR (exhibit #3)
for a map of existing basin layouts. Basin EX-1 encompasses the majority of the lot and the
currently being constructed access road. Bain EX-2 encompasses the Irrigation ditch and area
on the easterly side of the property.
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Historic Flow Path One:
Runoff from basin EX-1 sheet flows to the northwest from the southeast corner of the lot.
The runoff continues to sheet flow past the property boundary into an existing roadside swale
along W. Smuggler St. before crossing Smuggler Street at the intersection of N. 8th and then
flows northerly along N. 8th . Once near Meadows Road, the flow continues to travel
northwesterly between two residences onto Sneaky lane and into a large, marshy looking
wetlands near Castle Creek. After flowing into Castle Creek, the stormwater runoff will join
the Roaring Fork River. Please see Exhibit #2. The location of the properties in the Castle
Creek drainage basin prevents excessive runoff from other offsite locations. The basin consists
of natural/historic grasses and plants. Design point one has been associated with the northwest
corner of the basin. Calculations for onsite flows pertain to this location.
Historic Flow Path two:
Runoff from basin EX-2 sheet flows from southeast to northeast on Lot 3. This basin
includes the irrigation ditch on the easterly side of the property. The runoff flows to the
irrigation ditch and northeasterly in the ditch to a pipe that flows under W. Smuggler Drive.
This basin consists of natural/historic grasses and plants. Design point two has been
associated with the northeast corner of the basin. Calculations for onsite flows pertain to this
location.
Table 1. Existing Basin Characteristics
BASIN AREA,
ACRES C, 10YR I, 10YR Q10-YEAR,
CFS C, 100YR I, 100 YR Q100-YEAR,
CFS
EX-1 0.117 0.15 3.15 0.06 0.35 5.02 0.21
EX-2 0.035 0.15 2.99 0.06 0.35 4.78 0.20
TOTAL 0.12 TOTAL 0.42
Existing historic release rates from the site release at Design Point 1 is at a rate of 0.06 cfs
(10yr) and 0.21cfs (100yr).
IV. DRAINAGE DESIGN CRITERIA
A. Criteria
This drainage study was prepared in conformance with the City of Aspen, Colorado Urban
Runoff Management Plan (URMP), dated April of 2010 and the revised sections dated
thereafter (December 2014). More than 1,000 square feet of area will be disturbed with the
proposed construction; therefore, the site is viewed as a Major Drainage Report per the
URMP. More than 25-percent of the site is being disturbed, so water quality for the entire site
will be necessary per the URMP. The existing site was analyzed in its historic condition (i.e.
no improvements). The offsite basin consisting of landscape area was analyzed as existing
(open space) per the URMP.
Water Quality Capture Volume (WQCV) will be determined for the site as per the URMP
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standards. The WQCV is defined as the treatment for up to the 80th percentile runoff event,
corresponding to between a 6-month to 1-year event. The WQCV was determined using the
equations and Figure 8.13 from Chapter 8 of the URMP. WQCV was calculated using the
effective imperviousness. The WQCV equation is: Volume (ft3)=WQCV in watershed inches
x 1 ft/12 in x area (acres) x 43,560 ft2/acre.
B. Hydrologic Criteria
The hydrologic methods for this study are outlined in the URMP from the City of Aspen,
Colorado (revised December 2014) and updates utilizing a Microsoft Excel spreadsheet set up
for the Rational Method calculations/equations.
The obtained rainfall amounts for each basin used the updated Figure 2.1 “IDF Curves for
Aspen, Colorado” in the URMP publication from the City of Aspen, Colorado. Using these
curves, the rainfall intensity corresponding to the 2-yr, 1-hr storm 10-yr, 1-hr storm, and 100-
yr, 1-hr storm event were determined based on the time of concentration for each basin.
Figure 3.3 from the URMP was used to determine the runoff coefficients for the 2-year, 10-
year and 100-year storm events since the soils were determined to be Type ‘B’ soils.
The Rational Method was used for historic and proposed flowrates as outlined in the URMP
calculations/equations. The proposed WQ underground structure was sized using the URMP
methodology and the required detention for the entire tributary area of the site. The required
detention was determined using the methodology described in the URMP for a drywell with a
controlled outlet.
Runoff is not capable of discharging to a storm sewer system or directly into the river;
therefore, detention beyond WQCV is required for the site runoff. Existing and proposed
grades do not allow an outlet structure to discharge historic release rates for small events,
so runoff cannot discharge out of the bio-retention ponds until the water surface elevation
reaches the weir crest. Due to this condition, required detention calculations have been
modified for the storage volume used in design. The amount of storage required was
determined by calculating full detention until the runoff hydrograph intersects the outflow
hydrograph. By providing full detention until the runoff hydrograph reaches the 100-year
peak flowrate, the proposed system is capable of detaining 100-year storage volumes while
keeping the weir discharge to 100-year historic peak flowrates or less. Hydrograph
calculations for detention can be found in the appendices under drywell detention.
A portion of the drywell is within 10’ of the foundation and a liner has been provided to allow
no percolation within the section that is 10’ from the foundation. The drywell calculations
have been adjusted to subtract the gravel voids volume as well as the surface area required for
proper percolation. Additionally it is noted that the drywell is within 10’ of the property to
the east, however the irrigation ditch provides a minimum of a twenty foot buffer to any
possible structure that could be located on that lot.
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All charts and figures mentioned from the URMP are located in the last section of the
appendices under the “Aspen Charts/Figures” section.
C. Hydraulic Criteria
Lot 3 will have roof drains and patio drains piped to the pond, a swale will also conveys
stormwater runoff from the west portion of the site and driveway trench drains. There is
also a pipe that allows overflow from the pond to the drywell that has been sized for the 100-
year event. See basin descriptions below for explanation.
Lot 3 has a trench drain in the driveway that was calculated utilizing the Hydrology channel
calculator with AutoCAD’s system. The trench drain has the ability to carry the 100-year
event for the small portion that it collects.
We calculated the 10 and 100-year depths for the swale, as well as 2 pipes within the system
that carry the stormwater flows to the pond and drywell. The swale and storm pipes have been
sized per Civil 3D Hydraflow Express utilizing Manning’s equation. The 6” pipe is located at
the overflow inlet and discharges into the drywell. The 4” pipe conveys runoff from the deck
drains, downspouts and patio inlet that will discharge into the drywell. During a 100yr storm,
the design capacities for the 6” and 4” pipes are 50% and 58% of the pipe depth, respectively.
See basin descriptions below for explanation.
WQCV and required detention volumes will be stored in the bioretention pond and drywell,
which will percolate into the silty sandy gravel/cobble underneath and around the drywell.
The drywell was designed to accommodate 151.7 CF until the point of overflow. The drywell
meets the total required detention of 135 CF, including 89.6CF of WQCV per the 1.5 factor
calculated against the overall site requirements. This leaves 16.7 CF of excess capacity, not
including the additional storage provided by the pond. The drywell and pond will collect
storm water from the site via pipes and swales, which convey runoff to the pond and drywell
with minimum slopes of 2.0% in swales and 2.0% in pipes per the design documents. The
proposed drywell detention will drain into the surrounding soil within the 24-hour
requirement. The drywell has a proposed percolation area of 111SF that exceeds the required
89SF. Hydraulic conductivity used to calculate the required area of percolation was
determined using the Engineering Properties of Unified Soil Classes in the NRCS National
Engineering Handbook and soil class GM-GP, as specified in the soils report. Drain down
calculations can be found under drywell detention in the appendices. Percolation results
(exhibit #7) of 2 to 4 minutes per inch were determined from the percolation test performed on
Lot 3.
If the drywell and pond water level surpasses the proposed detention, then the system will
overflow via a broad crested concrete weir with a length of 1.25 feet and a notch depth of 0.25
feet. This will allow storm-water to leave the site at less than the historic and proposed 10-
year and 100-year flowrates. See appendices for weir release calculations.
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D. Site Constraints
The site is mainly clear of any onsite issues, but has disturbance areas within tree driplines.
The site is vegetated with native grasses brush and trees.
E. Easements, Irrigation Facilities, Waterways
A 20-foot wide access and utility easement runs through the site. There is also a 20’ irrigation
easement that runs through the easterly portion of the site. There are standard zoning setbacks
from property lines. These setbacks do not affect the overall site drainage design.
V. DRAINAGE FACILITY DESIGN.
A. General Concept
The proposed site plan calls for a new single family home, patios and sidewalks, drainage
facilities, and associated landscaping. A drywell and pond are proposed to be constructed on
the northwest side of the property. The pond and drywell will allow for the capture of the
required WQCV and detention per the URMP code. The existing swale along Smuggler Street
will carry the site overflow to the corner of Smuggler Street and North 8th Street. Historically,
a total rate of 0.21cfs (100YR) left the site as sheet flow to the northwest. In the proposed
condition, a total of no more than 0.21cfs (100YR) will leave the site after flowing to the
drywell and pond, which has excess storage capacity to reduce the offsite flowrate, rather than
sheet flow directly to the neighboring property.
The storm water facilities designed within this report focuses on collection and distribution to
the pond and drywell system. Due to constraints, this is the most feasible design for the site.
The grass lined swales and roof drains will allow for capture of all hardscape water and the
transfer of that water to the bio-pond then drywell for required WQCV and detention on the
site. The infiltration drywell will also have a water quality section due to untreated flows
being able to overflow into it, but a majority of the site WQCV will be within the bio-retention
pond. A site-specific geotechnical soil study was completed for this site, with gradation of the
soils and percolation test provided (Exhibit #7). As stated above, this drywell will drain
within the required 24 hours.
The 9 Principles for storm water quality management were followed during the design process
to create the best storm water design and water quality management for this particular site and
design concept.
Principle No. 1: From day one of all projects that HCE is reviewing we are always pushing
storm water, detention and WQ structures on the architects and landscape planners. In this
case we have a limited space for these features due to the preservation of existing trees and
landscape and the prevention of disturbed areas near other trees near the site. The new home
with the associated landscaping has just enough spacing to allow the drywell and pond on the
north side of the property. The drywell does fall within 10’ from the building foundation and
will have an impermeable liner within 10’ of the foundation to not allow percolation within
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10’ of the foundation. With the site constraints, the use of swales and the pond to store and
convey the stormwater all allows for a 13’ deep 4’ diameter drywell along with the pond to be
the most appropriate drainage design for this location.
Principle No. 2: The proposed redevelopment allows a vast majority of runoff from onsite,
impervious areas to be directed to the stormwater quality treatment system. Pervious terrain
or ground cover surround the remaining areas. The main structure is proposed to be built in
the northern area of the site where stormwater flows will travel around the site in grass lined
swales and pipe to provide treatment before entering the bioretention pond and then drywell.
Over detention also provides additional attenuation of storms to help reduce impacts by
reducing flows to surrounding properties.
Principle No. 3: The proposed changes to the site will increase impervious area on the
property.
Principle No. 4: The proposed removal of various pervious areas within the PR-1 basin
increases runoff rates. The increased contact between stormwater and the adequately sloped
soil will support infiltration and prevent ponding, thus reducing runoff volume. Disturbance
within saved tree driplines will be avoided as much as possible. The proposed redevelopment
will more closely match natural conditions than the existing features onsite and will add more
intensive and pervious landscaping than the natural conditions.
Principle No. 5: The pond and drywell being oversized will reduce small storm runoff from
the site and will accommodate for 10yr or 100yr storm events. The pond capacity includes the
required WQCV.
Principle No. 6: The stormwater facilities on this site take great care to direct water away from
the neighboring property and to appropriate facilities, resulting in reduced flow leaving the
site. This will improve the impact of stormwater on neighboring properties.
Principle No. 7: The treatment train for this site is limited, but mostly invisible to the public
in nature. The addition of stormwater back into the ground in a fast method, such as a drywell,
adds to the WQ process for the stormwater and recharges the area’s aquafers in a faster
manner that just stormwater runoff itself.
Principle No. 8: All of the onsite facilitates are easily accessible for cleaning and inspection.
The drywell will have a 24” removable grate for easy access and cleaning in the event that the
system needs maintenance or repair.
Principle No. 9: There are no steep or deep channels being proposed that could cause tripping
or fall hazards. All methods of actual treatment and storage are out of the public’s site and
allow safe passage.
The proposed site is divided into three onsite drainage basins and one offsite basin. Refer to
sheet PRDR, Exhibit #4, in the exhibit section for a map of the proposed basins and drainage
design.
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Basin PR-1 consists of the westerly side of the lot and approximately half of the proposed
home. This basin also includes a sidewalk on the front of the home and garage driveway. The
pond on the north side of the lot is also included in this basin. The drainage from PR-1 is
routed along the westerly side of the property around the front of the home into the pond.
Driveway drainage is captured with trench drains and discharged into the proposed swale at
design point 1. The flows release at design point 2 into the bioretention pond. The site
overflow is located in this basin at the pond weir and discharges at design point 5. This only
happens once the pond and drywell have been filled and then will release at the historic 10 and
100-year rates.
Basin PR-2 consists of the easterly side of the lot and approximately half of the proposed
home. Additionally, the drywell is included in this basin. This basin includes a pipe from an
upper deck and patio drains that will drain to the drywell. The drainage from PR-2 is routed
along the easterly side of the property around the front of the home and into the pond and the
drywell in basin PR-1. The flows release at design point 3.
Basin PR-3 consists of the irrigation ditch on the easterly side of the property. The runoff
flows to the irrigation ditch and northeasterly in the ditch to a pipe that flows under W.
Smuggler Street. This basin consists of natural/historic grasses and plants. . The flows release
at design point 4 into the ditch into a culvert and across W. Smuggler St.
Basin OS-1 consists of the alley that is currently being completed with the permit for the alley
improvements. This small basin sheet flows to the previously mentioned trench drains in
basin PR-1 at design point 1.
The design for proposed conditions on the site satisfies WQCV and the stormwater detention
requirements. Table 2, is a summary of the proposed basins.
Table 2. Proposed Basin Characteristics
BASIN AREA,
ACRES C, 10YR I, 10YR Q10-YEAR,
CFS C, 100YR I, 100 YR Q100-YEAR,
CFS
PR-1 0.062 0.55 3.96 0.14 0.64 6.33 0.25
PR-2 0.050 0.54 3.96 0.11 0.63 6.33 0.20
PR-3 0.040 0.15 2.98 0.02 0.35 4.75 0.07
OS-1 0.007 0.92 3.96 0.03 0.96 6.33 0.04
TOTAL 0.30 TOTAL 0.56
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B. Low Impact Site Design
The proposed site design incorporates as much low impact site design criteria from the URMP
as is site feasible. Grass lined swales will convey the proposed flows to the designed pond
and drywell system located near the north property line. All storm water generated by the
home will be conveyed through the bio-pond and drywell, thus reducing the transfer of
pollutants to the City of Aspen storm sewer system and the Castle Creek and Roaring Fork
River release point.
C. Specific Details
The composite impervious percentage for each basin and corresponding WQCV can be
located in Table 3, below. The imperviousness was then used to determine the WQCV in
watershed inches on Figure 8.13. Level 1 adjustment was not used for any of the basins to be
conservative since this site is very flat and has a minimal amount of release locations
available. The system utilized for the WQCV is capable of capturing the volume.
Table 3. Proposed WQCV Table
BASIN
AREA
(S.F.)
IMPERVIOUS
AREA (SF)
PERCENT
IMPERVIOUS
WQCV (Watershed
inches)
WQCV
(CF)
PR-1 2,716 2,000 73.6% 0.150 33.9
PR-2 2,194 1,566 71.4% 0.145 26.5
TOTAL 4,909 3,565 72.6% 0.146 59.7
D. Operation and Maintenance
The bio retention pond will need to be inspected and cleared of rubbish and debris quarterly to
make sure that the filter media has not become clogged and is functioning properly. The
detention areas shall also be inspected after large storm events to determine if the filter media
is functioning properly. If standing water is observed after small events, then clogging may be
occurring in the filter material. The top three inches of the filter media shall be scarified
yearly or more frequently to obtain optimum infiltration of surface runoff. If water is pooling,
then the filter material may need to be scarified more frequently. If the filter material
continues to fail, then the top six inches of the sand material shall be removed and replaced.
This may occur every two to five years.
The bio retention ponds will need to be mowed to keep weeds down. The grass shall be two to
four inches tall in irrigated areas or four to six-inches tall in non irrigated areas per the URMP.
The sandy loam and landscape material may need to be removed and replaced when it
becomes clogged and can no longer infiltrate the storm water runoff in an acceptable time. If
drain times are longer than 12 hours for the WQCV, then the filter media may need to be
removed and replaced with fresh filter media.
The grass conveyance swales will be kept up with regular mowing with a bagger to keep fine
particles out of the upper layer of the system as much as possible. The swales will also need
4/04/2019
Include a more detailed description of the
operation of the proposed system.
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to be inspected after heavy rainstorms to remove any large debris that may have collected and
they will be raked quarterly and during the fall months prior to snow fall to remove any built
up tree debris that may fall during those months so they are prepared for spring thaw flows.
The drywell will need to be inspected and cleared of rubbish and debris quarterly to make sure
that the filter/riser pipe has not become clogged and is functioning properly. Routinely
evaluate the drain-down time of the drywell to ensure the max time of 24 hours is not being
exceeded. If drain-down times are exceeding the max, drain the dyrwell via pumping and
clean out the percolation area. The drywell grate must also be inspected to make sure it has
not clogged. Review of the overflow structure should occur at least every 6 months or after
large storm events.
The owners or owner’s representative will be responsible for the maintenance and upkeep of
the drainage facilities. The property owner shall dispose of sediment and any other waste
material removed from a reservoir at a suitable disposal site and in compliance with local,
state, and federal waste regulations.
VI. CONCLUSION
A. Compliance with Standards
This drainage report has been prepared in accordance with City of Aspen Regulations. The
proposed storm water facilities will capture the WQCV and the detention for the site. Water
leaving the site will be controlled at the historic release point.
B. Drainage Concept
The proposed drainage design will be effective in controlling any adverse downstream impacts
on landowners or structures by having the storm water leave the site directed toward City
stormwater systems instead of uncontrolled drainage ways as historically exist. Water quality
issues will not be a concern as the runoff carrying pollutants is being captured and stored in
the proposed pond and drywell structure.
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VII. References
City of Aspen, Colorado: Design and Construction Standards, June 2005.
City of Aspen, Colorado: Urban Runoff Management Plan. April 2010, Sept 2014 Update.
WRC Engineering, Inc. “Storm Drainage Master Plan for the City of Aspen, Colorado”.
November 2001.
HP Geotech, Inc. “Subsoil Study for Foundation design, Proposed Residence Lot 3, Ranger
Station Subdivision, 851 West Smuggler Street, Aspen, CO” dated March 13, 2017, Job
Number 17-7-182.
UDFCD. www.udfcd.org.
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EXHIBITS
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Exhibit #1 – Vicinity Map
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Exhibit #2 – Flow Path
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Exhibit #3 – Existing Drainage Basins
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Exhibit #4 – Proposed Drainage Basins
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Exhibit #5 – FEMA
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Exhibit #6 - USDA Web Soils Survey
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Hydrologic Soil Group—Aspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
3/20/2019
Page 1 of 4
39° 11' 47'' N
10
6
°
4
9
'
5
4
'
'
W
39° 11' 47'' N
10
6
°
4
9
'
4
7
'
'
W
39° 11' 44'' N
10
6
°
4
9
'
5
4
'
'
W
39° 11' 44'' N
10
6
°
4
9
'
4
7
'
'
W
N
Map projection: Web Mercator Corner coordinates: WGS84
0 35 70 140 210
Feet
0 10 20 40 60
Meters
Map Scale: 1:754 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
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107—Uracca, moist-Mergel complex, 1 to 6 percent slopes, extremely s
Map Unit Setting
National map unit symbol: jq4g
Elevation: 6,800 to 8,400 feet
Mean annual precipitation: 16 to 19 inches
Mean annual air temperature: 40 to 43 degrees F
Frost-free period: 75 to 95 days
Farmland classification: Not prime farmland
Map Unit Composition
Uracca, moist, and similar soils: 50 percent
Mergel and similar soils: 40 percent
Estimates are based on observations, descriptions, and transects of the
mapunit.
Description of Uracca, Moist
Setting
Landform: Structural benches, valley sides, alluvial fans
Down-slope shape: Linear
Across-slope shape: Linear
Parent material: Mixed alluvium derived from igneous and metamorphic rock
Typical profile
H1 - 0 to 8 inches: cobbly sandy loam
H2 - 8 to 15 inches: very cobbly sandy clay loam
H3 - 15 to 60 inches: extremely cobbly loamy sand
Properties and qualities
Slope: 1 to 6 percent
Depth to restrictive feature: More than 80 inches
Natural drainage class: Well drained
Runoff class: Low
Capacity of the most limiting layer to transmit water (Ksat):Moderately high to
high (0.20 to 2.00 in/hr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum in profile: 10 percent
Available water storage in profile: Very low (about 2.6 inches)
Interpretive groups
Land capability classification (irrigated): 6s
Land capability classification (nonirrigated): 6s
Hydrologic Soil Group: B
Ecological site: Stony Loam (R048AY237CO)
Other vegetative classification: Stony Loam (null_82)
Hydric soil rating: No
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Description of Mergel
Setting
Landform: Structural benches, valley sides, alluvial fans
Down-slope shape: Linear
Across-slope shape: Linear
Parent material: Glacial outwash
Typical profile
H1 - 0 to 8 inches: cobbly loam
H2 - 8 to 20 inches: very cobbly sandy loam
H3 - 20 to 60 inches: extremely stony sandy loam
Properties and qualities
Slope: 1 to 6 percent
Depth to restrictive feature: More than 80 inches
Natural drainage class: Well drained
Runoff class: Very low
Capacity of the most limiting layer to transmit water (Ksat):Moderately high to
high (0.60 to 6.00 in/hr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum in profile: 10 percent
Available water storage in profile: Low (about 3.3 inches)
Interpretive groups
Land capability classification (irrigated): 4s
Land capability classification (nonirrigated): 4s
Hydrologic Soil Group: A
Ecological site: Stony Loam (R048AY237CO)
Other vegetative classification: Stony Loam (null_82)
Hydric soil rating: No
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Exhibit #7 – HP Kumar Soil Study
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APPENDICES
4/04/2019
HYDROLOGIC
COMPUTATIONS
4/04/2019
HISTORIC CONDITIONS
4/04/2019
Lot 3, Ranger Station Subdivision
DRAINAGE REPORT
BY: BDB
CHECKED BY: RDN
DATE: 03-15-19
EX-1 5,101.3 0.117 0.0 0.0 0.08 0.15 0.35
EX-2 1,538.2 0.035 0.0 0.0 0.08 0.15 0.35
Type B Soils
5 YR RUNOFF
COEFFICIENT
10 YR RUNOFF
COEFFICIENT
100 YR RUNOFF
COEFFICIENTPERCENT IMPERVIOUSBASIN AREA (S.F.) AREA (ACRE) IMPERVIOUS AREA (SF)
4/04/2019
LOT 3, Ranger Station Subdivision, Aspen
DRAINAGE REPORT
BY: BDB
CHECKED BY: RDN
DATE: 03-15-19
REACH
Basin I P1-10yr P1-100yr Td
EX-1 3.15 0.77 8.7
EX-1 5.02 1.23 8.7
Basin I P1-10yr P1-100yr Td
EX-2 2.99 0.77 9.6
Tc EX-2 4.78 1.23 9.6
TC
Tc
10 YEAR
100 YEAR
To = [0.395 (1.1 - C5) SQRT(L)] / (S 0.333) EQUATION 3-4
C= 5 YR runoff coefficient from City of Aspen Urban Runoff Management Plan
Tc=To+Tt
INTENSITY I=88.8*p/((10+T)^1.052) EQUATION 2-1
P TAKEN FROM TABLES 2.2 AND 2.3
10.5
MINIMUM 5 MINUTES
8.7
EX-1BASIN
(MIN)
3.15
5.0
1
RATIONAL COEFFICIENT. C (FIGURE 3.2 OF URMP)
Rainfall Intenstity Chart EX-1
0.087
8.7
EX-1
92.44
0.08
0.0
FLOW LENGTH, L (TOTAL <300 FT.) (ft.)
AREA IDENTIFIER
To (MIN)OV
E
R
L
A
N
D
FL
O
W
LAND SLOPE, S (ft./ft.)
SURFACE DESCRIPTION
TR
A
V
E
L
T
I
M
E
FLOW SLOPE, S (ft./ft.) 0.0000
0FLOW LENGTH, L (ft.)
TRAVEL TIME = L/(60V) (min.)
FLOW VELOCITY, V (FIGURE *RO-1 UDFCD) (fps.)
URBAN CHECK = 10+L/180
5.02
6.0
EX-2
0.08
81.59
0.053
9.6
0
EX-2
2.99
4.78
Rainfall Intenstity Chart EX-2
0.0000
1
0.0
9.6
10.5
4/04/2019
CALCULATED BY: BDB STANDARD FORM SF-3
DATE: 03-15-19 STORM DRAINAGE SYSTEM DESIGN
CHECKED BY: RDN (RATIONAL METHOD PROCEDURE)
Contributing Area
AR
E
A
(
A
C
)
RU
N
O
F
F
C
O
E
F
F
.
Tc
(
M
I
N
)
C
*
A
(
A
C
)
I
(
I
N
/
H
R
)
Q
(
C
F
S
)
Tc
(
M
I
N
)
SU
M
(
C
*
A
)
(
A
C
)
I
(
I
N
/
H
R
)
Q
(
C
F
S
)
SL
O
P
E
(
%
)
CH
A
N
N
E
L
F
L
O
W
(C
F
S
)
DE
S
I
G
N
F
L
O
W
(C
F
S
)
SL
O
P
E
(
%
)
PI
P
E
S
I
Z
E
(
I
N
C
H
E
S
)
LE
N
G
T
H
(
F
T
)
VE
L
O
C
I
T
Y
(
F
P
S
)
Tt
(
M
I
N
)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)
DESIGN POINT 20.01 2.99 0.022 EX-2 0.035 0.15 9.6
DE
S
I
G
N
P
O
I
N
T
DIRECT RUNOFF
STRUCTURE NO.
TOTAL RUNOFF
PROJECT: LOT 3 RANGER STA. SUBDIVISION
JOB NO. 2181030.03
PIPE
DESIGN STORM: EXISTING 10 YEAR
TRAVEL TIME
REMARKS
CHANNEL
EX-11 8.70.15 0.02 0.06 DESIGN POINT 13.150.117
4/04/2019
CALCULATED BY: BDB STANDARD FORM SF-3
DATE: 03-15-19 STORM DRAINAGE SYSTEM DESIGN
CHECKED BY: RDN (RATIONAL METHOD PROCEDURE)
Contributing Area
AR
E
A
(
A
C
)
RU
N
O
F
F
C
O
E
F
F
.
Tc
(
M
I
N
)
C
*
A
(
A
C
)
I
(
I
N
/
H
R
)
Q
(
C
F
S
)
Tc
(
M
I
N
)
SU
M
(
C
*
A
)
(
A
C
)
I
(
I
N
/
H
R
)
Q
(
C
F
S
)
SL
O
P
E
(
%
)
CH
A
N
N
E
L
F
L
O
W
(C
F
S
)
DE
S
I
G
N
F
L
O
W
(C
F
S
)
SL
O
P
E
(
%
)
PI
P
E
S
I
Z
E
(
I
N
C
H
E
S
)
LE
N
G
T
H
(
F
T
)
VE
L
O
C
I
T
Y
(
F
P
S
)
Tt
(
M
I
N
)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)
DESIGN POINT 20.01 4.78 0.062 EX-2 0.035 0.35 9.6
JOB NO. 2181030.03
PROJECT: LOT 3 RANGER STA. SUBDIVISION
DESIGN STORM: EXISTING 100 YEAR
STRUCTURE NO.
DE
S
I
G
N
P
O
I
N
T
DIRECT RUNOFF TOTAL RUNOFF CHANNEL PIPE TRAVEL TIME
REMARKS
1 EX-1 0.117 0.35 8.7 0.04 5.02 0.21 DESIGN POINT 1
4/04/2019
PROPOSED CONDITIONS
4/04/2019
LOT 3, Ranger Station Subdivision, Aspen
DRAINAGE REPORT
BY: BDB
CHECKED BY: RDN
DATE: 03-15-19
PR-1 2,715.6 0.062 1,999.5 73.6 0.150 33.9 0.48 0.51 0.55 0.64
PR-2 2,193.8 0.050 1,565.9 71.4 0.145 26.5 0.46 0.50 0.54 0.63
PR-3 1,723.2 0.040 0.0 0.0 0.000 0.0 0.02 0.08 0.15 0.35
OS-1 312.8 0.007 312.8 100.0 0.260 6.8 0.89 0.90 0.92 0.96
TOTAL SITE 4,909.3 0.113 3,565.4 72.6 0.146 59.7
Time 1.5 for Drywell 89.6
10 YR RUNOFF
COEFFICIENT
100 YR RUNOFF
COEFFICIENT
WQCV (Watershed
inches) WQCV (CF)
5 YR RUNOFF
COEFFICIENT
Type B Soils
BASIN AREA (S.F.) AREA (ACRE)
IMPERVIOUS AREA
(SF)
PERCENT
IMPERVIOUS
2 YR RUNOFF
COEFFICIENT
4/04/2019
LOT 3, Ranger Station Subdivision, Aspen
DRAINAGE REPORT
BY: BDB
CHECKED BY: RDN
DATE: 03-15-19
REACH
Basin I P1-2yr P1-10yr P1-100yr Td
PR-1 2.42 0.47 5.0
PR-1 3.96 0.77 5.0
PR-1 6.33 1.23 5.0
Basin I P1-2yr P1-10yr P1-100yr Td
Tc PR-2 2.42 0.47 5.0
TC PR-2 3.96 0.77 5.0
Tc PR-2 6.33 1.23 5.0
2 YEAR INTENSITY Basin I P1-2yr P1-10yr P1-100yr Td
10 YEAR INTENSITY
100 YEAR INTENSITY PR-3 1.82 0.47 9.7
PR-3 2.98 0.77 9.7
To = [0.395 (1.1 - C5) SQRT(L)] / (S 0.333) EQUATION 3-4 PR-3 4.75 1.23 9.7
C= 5 YR runoff coefficient from City of Aspen Urban Runoff Management Plan
INTENSITY I=29p/((10+T)^0.789) EQUATION 2-1 Basin I P1-2yr P1-10yr P1-100yr Td
P TAKEN FROM TABLES 2.2 AND 2.3 WITHIN THE URMP
*INTENSITIES TAKEN FROM FIGURE 2.1 "IDF CURVES FOR ASPEN, COLORADO" FROM URMP OS-1 2.42 0.47 5.0
OS-1 3.96 0.77 5.0
OS-1 6.33 1.23 5.0
Rainfall Intenstity Chart PR-1
OV
E
R
L
A
N
D
FL
O
W
FLOW VELOCITY, V (FIGURE *RO-1 UDFCD) (fps.)
FLOW LENGTH, L (ft.)
TR
A
V
E
L
T
I
M
E
SURFACE DESCRIPTION
FLOW LENGTH, L (TOTAL <300 FT.) (ft.)
LAND SLOPE, S (ft./ft.)
PR-1
16.5
BASIN
MINIMUM 5 MINUTES
6.33
PR-1
3.96
2.42
RATIONAL COEFFICIENT. C (FIGURE 3.2 OF URMP) 0.510
AREA IDENTIFIER
FLOW SLOPE, S (ft./ft.)
(MIN)
TRAVEL TIME = L/(60V) (min.)
0.132
URBAN CHECK = 10+L/180
123.9
0.021
10.8
To (MIN)
5.0
2.17
1.9
2.8
1.0
PR-2
0.500
12.5
0.02
3.1
113.2
0.02
2.83
0.7
3.7
10.7
5.0
PR-2
2.42
3.96
6.33
OS-1
0.900
26.5
0.081
0.9
0.0
0
1
0.0
0.9
10.1
0.0
9.7
10.5
5.0
Rainfall Intenstity Chart PR-2
Rainfall Intenstity Chart PR-3
5.0
OS-1
PR-3
0.053
9.7
0.0
0
1
0.080
81.6
PR-3
1.82
2.98
4.75
Rainfall Intenstity Chart OS-1
2.42
3.96
6.33
4/04/2019
CALCULATED BY: BDB STANDARD FORM SF-3
DATE: 03-15-19 STORM DRAINAGE SYSTEM DESIGN
CHECKED BY: RDN (RATIONAL METHOD PROCEDURE)
Contributing Area
AR
E
A
(
A
C
)
RU
N
O
F
F
C
O
E
F
F
.
Tc
(
M
I
N
)
C
*
A
(
A
C
)
I
(
I
N
/
H
R
)
Q
(
C
F
S
)
Tc
(
M
I
N
)
SU
M
(
C
*
A
)
(
A
C
)
I
(
I
N
/
H
R
)
Q
(
C
F
S
)
SL
O
P
E
(
%
)
ST
R
E
E
T
F
L
O
W
(
C
F
S
)
DE
S
I
G
N
F
L
O
W
(
C
F
S
)
SL
O
P
E
(
%
)
PI
P
E
S
I
Z
E
(
I
N
C
H
E
S
)
LE
N
G
T
H
(
F
T
)
VE
L
O
C
I
T
Y
(
F
P
S
)
Tt
(
M
I
N
)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)
Design Point 11 PR-1 5.000.062 0.03 2.42
PROJECT: LOT 3 RANGER STA. SUBDIVISION
JOB NO. 2181030.03
DIRECT RUNOFF
0.07
STRUCTURE NO.
DE
S
I
G
N
P
O
I
N
T
REMARKS
DESIGN STORM: PROPOSED 2 YEAR
0.48
TRAVEL TIMEPIPESTREETTOTAL RUNOFF
2 PR-2 0.050 0.46 5.00 0.02 2.42 0.06 Design Point 2
3 OS-1 0.007 0.89 5.00 0.01 2.42 0.02 Design Point 4
3 PR-3 0.040 0.02 9.68 Design Point 30.00 1.82 0.00
4/04/2019
CALCULATED BY: BDB STANDARD FORM SF-3
DATE: 03-15-19 STORM DRAINAGE SYSTEM DESIGN
CHECKED BY: RDN (RATIONAL METHOD PROCEDURE)
Contributing Area
AR
E
A
(
A
C
)
RU
N
O
F
F
C
O
E
F
F
.
Tc
(
M
I
N
)
C
*
A
(
A
C
)
I
(
I
N
/
H
R
)
Q
(
C
F
S
)
Tc
(
M
I
N
)
SU
M
(
C
*
A
)
(
A
C
)
I
(
I
N
/
H
R
)
Q
(
C
F
S
)
SL
O
P
E
(
%
)
ST
R
E
E
T
F
L
O
W
(
C
F
S
)
DE
S
I
G
N
F
L
O
W
(
C
F
S
)
SL
O
P
E
(
%
)
PI
P
E
S
I
Z
E
(
I
N
C
H
E
S
)
LE
N
G
T
H
(
F
T
)
VE
L
O
C
I
T
Y
(
F
P
S
)
Tt
(
M
I
N
)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)
0.03 Design Point 4
Design Point 2
1 OS-1 0.007 0.92 5.00 0.01 3.96
0.03 3.96 0.113 PR-2 0.050 0.54 5.00
0.14 Design Point 1
TRAVEL TIME
REMARKS
1,2,5 PR-1 0.062 0.55 5.00 0.03 3.96
JOB NO. 2181030.03
PROJECT: LOT 3 RANGER STA. SUBDIVISION
DESIGN STORM: PROPOSED 10 YEAR
STRUCTURE NO.
DE
S
I
G
N
P
O
I
N
T
DIRECT RUNOFF TOTAL RUNOFF STREET PIPE
4 PR-3 0.040 0.15 9.68 Design Point 30.01 2.98 0.02
4/04/2019
CALCULATED BY: BDB STANDARD FORM SF-3
DATE: 03-15-19 STORM DRAINAGE SYSTEM DESIGN
CHECKED BY: RDN (RATIONAL METHOD PROCEDURE)
Contributing Area
AR
E
A
(
A
C
)
RU
N
O
F
F
C
O
E
F
F
.
Tc
(
M
I
N
)
C
*
A
(
A
C
)
I
(
I
N
/
H
R
)
Q
(
C
F
S
)
Tc
(
M
I
N
)
SU
M
(
C
*
A
)
(
A
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(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)
0.04 Design Point 4
Design Point 2
1 OS-1 0.007 0.96 5.00 0.01 6.33
0.03 6.33 0.203 PR-2 0.050 0.63 5.00
0.25 Design Point 1
TRAVEL TIME
REMARKS
1,2,5 PR-1 0.062 0.64 5.00 0.04 6.33
JOB NO. 2181030.03
PROJECT: LOT 3, RANGER STA. SUBDIVISION
DESIGN STORM: PROPOSED 100 YEAR
STRUCTURE NO.
DE
S
I
G
N
P
O
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N
T
DIRECT RUNOFF TOTAL RUNOFF STREET PIPE
4 PR-3 0.040 0.35 9.68 Design Point 30.01 4.75 0.07
4/04/2019
HYDRAULIC
COMPUTATIONS
4/04/2019
SWALE & PIPE CALCULATIONS
4/04/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Mar 19 2019
PROPOSED SWALE AT 10YR PEAK FLOW (PR-1+ OS-1)
Triangular
Side Slopes (z:1) = 3.00, 3.00
Total Depth (ft) = 0.50
Invert Elev (ft) = 7896.75
Slope (%) = 2.00
N-Value = 0.024
Calculations
Compute by: Known Q
Known Q (cfs) = 0.17
Highlighted
Depth (ft) = 0.19
Q (cfs) = 0.170
Area (sqft) = 0.11
Velocity (ft/s) = 1.57
Wetted Perim (ft) = 1.20
Crit Depth, Yc (ft) = 0.19
Top Width (ft) = 1.14
EGL (ft) = 0.23
0 .5 1 1.5 2 2.5 3 3.5 4
Elev (ft)Depth (ft)Section
7896.00 -0.75
7896.50 -0.25
7897.00 0.25
7897.50 0.75
7898.00 1.25
Reach (ft)
4/04/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Mar 19 2019
PROPOSED SWALE AT 100YR PEAK FLOW (PR-1+ OS-1)
Triangular
Side Slopes (z:1) = 3.00, 3.00
Total Depth (ft) = 0.50
Invert Elev (ft) = 7896.75
Slope (%) = 2.00
N-Value = 0.024
Calculations
Compute by: Known Q
Known Q (cfs) = 0.29
Highlighted
Depth (ft) = 0.23
Q (cfs) = 0.290
Area (sqft) = 0.16
Velocity (ft/s) = 1.83
Wetted Perim (ft) = 1.45
Crit Depth, Yc (ft) = 0.23
Top Width (ft) = 1.38
EGL (ft) = 0.28
0 .5 1 1.5 2 2.5 3 3.5 4
Elev (ft)Depth (ft)Section
7896.00 -0.75
7896.50 -0.25
7897.00 0.25
7897.50 0.75
7898.00 1.25
Reach (ft)
4/04/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Wednesday, Mar 20 2019
4in Pipe @ PR-2 10YR Flowrate
Circular
Diameter (ft) = 0.33
Invert Elev (ft) = 7896.16
Slope (%) = 2.00
N-Value = 0.010
Calculations
Compute by: Known Q
Known Q (cfs) = 0.11
Highlighted
Depth (ft) = 0.13
Q (cfs) = 0.110
Area (sqft) = 0.03
Velocity (ft/s) = 3.50
Wetted Perim (ft) = 0.45
Crit Depth, Yc (ft) = 0.19
Top Width (ft) = 0.32
EGL (ft) = 0.32
0 1
Elev (ft)Section
7895.75
7896.00
7896.25
7896.50
7896.75
7897.00
Reach (ft)
4/04/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Wednesday, Mar 20 2019
4in Pipe @ PR-2 100YR Flowrate
Circular
Diameter (ft) = 0.33
Invert Elev (ft) = 7896.16
Slope (%) = 2.00
N-Value = 0.010
Calculations
Compute by: Known Q
Known Q (cfs) = 0.20
Highlighted
Depth (ft) = 0.19
Q (cfs) = 0.200
Area (sqft) = 0.05
Velocity (ft/s) = 3.91
Wetted Perim (ft) = 0.57
Crit Depth, Yc (ft) = 0.26
Top Width (ft) = 0.33
EGL (ft) = 0.43
0 1
Elev (ft)Section
7895.75
7896.00
7896.25
7896.50
7896.75
7897.00
Reach (ft)
4/04/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Wednesday, Mar 20 2019
6in Pipe @ Entire Site 10YR Flowrate
Circular
Diameter (ft) = 0.50
Invert Elev (ft) = 7893.60
Slope (%) = 2.00
N-Value = 0.010
Calculations
Compute by: Known Q
Known Q (cfs) = 0.28
Highlighted
Depth (ft) = 0.18
Q (cfs) = 0.280
Area (sqft) = 0.06
Velocity (ft/s) = 4.38
Wetted Perim (ft) = 0.64
Crit Depth, Yc (ft) = 0.27
Top Width (ft) = 0.48
EGL (ft) = 0.48
0 1 2
Elev (ft)Section
7893.00
7893.50
7894.00
7894.50
7895.00
Reach (ft)
4/04/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Wednesday, Mar 20 2019
6in Pipe @ Entire Site 100YR Flowrate
Circular
Diameter (ft) = 0.50
Invert Elev (ft) = 7893.60
Slope (%) = 2.00
N-Value = 0.010
Calculations
Compute by: Known Q
Known Q (cfs) = 0.49
Highlighted
Depth (ft) = 0.25
Q (cfs) = 0.490
Area (sqft) = 0.10
Velocity (ft/s) = 4.96
Wetted Perim (ft) = 0.79
Crit Depth, Yc (ft) = 0.36
Top Width (ft) = 0.50
EGL (ft) = 0.63
0 1 2
Elev (ft)Section
7893.00
7893.50
7894.00
7894.50
7895.00
Reach (ft)
4/04/2019
TRENCH/SLAB DRAIN CALCULATIONS
4/04/2019
Inlet Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Mar 19 2019
6 in. Driveway Trench Drain
Drop Grate Inlet
Location = On grade
Curb Length (ft) = -0-
Throat Height (in) = -0-
Grate Area (sqft) = -0-
Grate Width (ft) = 20.00
Grate Length (ft) = 0.50
Gutter
Slope, Sw (ft/ft) = 0.020
Slope, Sx (ft/ft) = 0.020
Local Depr (in) = -0-
Gutter Width (ft) = 20.00
Gutter Slope (%) = 12.00
Gutter n-value = 0.016
Calculations
Compute by: Known Q
Q (cfs) = 0.29
Highlighted
Q Total (cfs) = 0.29
Q Capt (cfs) = 0.28
Q Bypass (cfs) = 0.01
Depth at Inlet (in) = 0.12
Efficiency (%) = 98
Gutter Spread (ft) = 21.00
Gutter Vel (ft/s) = 1.41
Bypass Spread (ft) = 21.00
Bypass Depth (in) = 0.12
4/04/2019
Inlet Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Monday, Mar 18 2019
12 in. Driveway Trench Drain
Drop Grate Inlet
Location = Sag
Curb Length (ft) = -0-
Throat Height (in) = -0-
Grate Area (sqft) = 10.20
Grate Width (ft) = 1.00
Grate Length (ft) = 17.00
Gutter
Slope, Sw (ft/ft) = 0.120
Slope, Sx (ft/ft) = 0.120
Local Depr (in) = -0-
Gutter Width (ft) = 1.00
Gutter Slope (%) = -0-
Gutter n-value = -0-
Calculations
Compute by: Known Q
Q (cfs) = 0.29
Highlighted
Q Total (cfs) = 0.29
Q Capt (cfs) = 0.29
Q Bypass (cfs) = -0-
Depth at Inlet (in) = 0.23
Efficiency (%) = 100
Gutter Spread (ft) = 1.32
Gutter Vel (ft/s) = 4.60
Bypass Spread (ft) = -0-
Bypass Depth (in) = -0-
4/04/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Monday, Mar 18 2019
Trench in Walkway at PR-1+OS-1 10YR Peak Flowrate
Rectangular
Bottom Width (ft) = 0.50
Total Depth (ft) = 0.33
Invert Elev (ft) = 7896.73
Slope (%) = 3.00
N-Value = 0.013
Calculations
Compute by: Known Q
Known Q (cfs) = 0.17
Highlighted
Depth (ft) = 0.10
Q (cfs) = 0.170
Area (sqft) = 0.05
Velocity (ft/s) = 3.40
Wetted Perim (ft) = 0.70
Crit Depth, Yc (ft) = 0.16
Top Width (ft) = 0.50
EGL (ft) = 0.28
0 .1 .2 .3 .4 .5 .6 .7
Elev (ft)Depth (ft)Section
7896.00 -0.73
7896.50 -0.23
7897.00 0.27
7897.50 0.77
7898.00 1.27
Reach (ft)
4/04/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Monday, Mar 18 2019
Trench in Walkway at PR-1+OS-1 100YR Peak Flowrate
Rectangular
Bottom Width (ft) = 0.50
Total Depth (ft) = 0.33
Invert Elev (ft) = 7896.73
Slope (%) = 3.00
N-Value = 0.013
Calculations
Compute by: Known Q
Known Q (cfs) = 0.29
Highlighted
Depth (ft) = 0.15
Q (cfs) = 0.290
Area (sqft) = 0.08
Velocity (ft/s) = 3.87
Wetted Perim (ft) = 0.80
Crit Depth, Yc (ft) = 0.22
Top Width (ft) = 0.50
EGL (ft) = 0.38
0 .1 .2 .3 .4 .5 .6 .7
Elev (ft)Depth (ft)Section
7896.00 -0.73
7896.50 -0.23
7897.00 0.27
7897.50 0.77
7898.00 1.27
Reach (ft)
4/04/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Mar 19 2019
TRENCH IN WALKWAY @ (PR-1)+9PR-2)+(OS-1) 10YR PEAK FLOWRATE
Rectangular
Bottom Width (ft) = 0.50
Total Depth (ft) = 0.92
Invert Elev (ft) = 7895.99
Slope (%) = 1.67
N-Value = 0.013
Calculations
Compute by: Known Q
Known Q (cfs) = 0.28
Highlighted
Depth (ft) = 0.18
Q (cfs) = 0.280
Area (sqft) = 0.09
Velocity (ft/s) = 3.11
Wetted Perim (ft) = 0.86
Crit Depth, Yc (ft) = 0.22
Top Width (ft) = 0.50
EGL (ft) = 0.33
0 .1 .2 .3 .4 .5 .6 .7
Elev (ft)Depth (ft)Section
7895.00 -0.99
7895.50 -0.49
7896.00 0.01
7896.50 0.51
7897.00 1.01
Reach (ft)
4/04/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Monday, Mar 18 2019
Trench in Walkway at (PR-1)+(PR-2)+(OS-1) 100YR Overflow Swale Peak Flowrate
Rectangular
Bottom Width (ft) = 0.50
Total Depth (ft) = 0.92
Invert Elev (ft) = 7895.99
Slope (%) = 1.67
N-Value = 0.013
Calculations
Compute by: Known Q
Known Q (cfs) = 0.49
Highlighted
Depth (ft) = 0.27
Q (cfs) = 0.490
Area (sqft) = 0.14
Velocity (ft/s) = 3.63
Wetted Perim (ft) = 1.04
Crit Depth, Yc (ft) = 0.32
Top Width (ft) = 0.50
EGL (ft) = 0.47
0 .1 .2 .3 .4 .5 .6 .7
Elev (ft)Depth (ft)Section
7895.00 -0.99
7895.50 -0.49
7896.00 0.01
7896.50 0.51
7897.00 1.01
Reach (ft)
4/04/2019
DETENTION & DRYWELL CALCULATIONS
4/04/2019
Hydrology Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Monday, Mar 18 2019
Required Storage with EX-1 100yr Historic Release Rate
Hydrograph type = Rational Peak discharge (cfs) = 0.427
Storm frequency (yrs) = 100 Time interval (min) = 1
Drainage area (ac) = 0.113 Runoff coeff. (C) = 0.64
Rainfall Inten (in/hr) = 5.903 Tc by FAA (min) = 6
IDF Curve = AspenIDFcurve.IDF Rec limb factor = 1.00
Hydrograph Volume = 154 (cuft); 0.004 (acft)
0 5 10 15
Q (cfs)
0.00 0.00
0.05 0.05
0.10 0.10
0.15 0.15
0.20 0.20
0.25 0.25
0.30 0.30
0.35 0.35
0.40 0.40
0.45 0.45
0.50 0.50
Q (cfs)
Time (min)
Runoff Hydrograph
100-yr frequency
Runoff Hyd - Qp = 0.43 (cfs)Outflow Hyd *Req. Stor = 78 (cuft) *
* Estimated
Additional Required Detention=57 cuft
Total Req. Storage:135 cuft
4/04/2019
FAA Formula Tc Worksheet
Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve
Rational
Required Storage with EX-1 100yr Historic Release Rate
Description
Flow length (ft) = 140.34
Watercourse slope (%) = 4.60
Runoff coefficient (C) = 0.64
Time of Conc. (min) = 6
4/04/2019
Cone Section Opening Volume to Width of Depth of gravel Dia of Percent Concrete Cylinde Cone section Ht.
(ft) Detain (cf) Gravel (ft) Below M.H. (ft) M.H. Voids (%) Thickness (in) (ft)
2 135.0 2.0 1 4 30 5 2.0
Volume in gravel starts at: 4
Area of M.H. (sqft) 12.6
Area of Gravel (sqft) 21.5
Area of Concrete Cylinder (s q 5.78
Volume of 6" PCC Slab (sqft) 6.3
Volume of Gravel Bottom 19.9 ↓
Depth Volume of Vol of Gravel Vol of Drywell Vol of Drywell Vol of Total Volume
Varied Gravel Voids Conic Section Cyl. Section Drywell Volume Met
(f t) (c f) (c f) (c f) (c f) (c f) (c f)
1 0.0 0.0 0.0 0.0 0.0 0.0 no
2 0.0 0.0 0.0 0.0 0.0 0.0 no
3 0.0 0.0 0.0 0.0 0.0 0.0 no
4 19.9 6.0 0.0 0.0 0.0 6.0 no
5 41.4 12.4 0.0 12.6 6.3 18.7 no
6 62.8 18.9 0.0 25.1 18.8 37.7 no
7 84.3 25.3 0.0 37.7 31.4 56.7 no
8 105.8 31.7 0.0 50.3 44.0 75.7 no
9 127.2 38.2 0.0 62.8 56.5 94.7 no
10 148.7 44.6 0.0 75.4 69.1 113.7 no
11 170.2 51.1 0.0 88.0 81.7 132.7 no
12 191.6 57.5 0.0 100.5 94.2 151.7 Meets Min.
13 213.1 63.9 0.0 113.1 106.8 170.7 Meets Min.
Transmissivity Calc.
Depth of Gravel (ft)= 8
K from NRCS National Engineering Handbook, figure 3 ‐10, soil class GM
AP=(VR)/(K)(43,200)
AP/2=Total area of sides (sf)111.00
VR = runoff volume (cf)135.0
K= Hydraulic Conductivity (ft/s 0.000035
Area of Percolation Required 89.29
Tele: (970) 945-8676 - Fax (970) 945-2555
Calculation of Drywell and Gravel
4' DIAMETER, 12' DEEP DRYW ELL
1517 BLAKE AVENUE
Glenwood Springs, CO 81601
Variables
Per soil s tudy: Perc.=2-4mi n/in; S oil type GM-GP (k per SCS E ngineeri ng Fi eld Manual)
Volume of 6" slab is deducted from volume of drywell────┐
LOT 3, RANGER STATION SUBDIVISION
DRAINAGE STUDY DRYW ELL CALCULATIONS
Date: 03-15-19 HCE #: 2181030.03
Drywell Calculations
4/04/2019
WEIR CALCULATIONS
4/04/2019
Weir Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Mar 19 2019
Weir @ Proposed Site 10YR Peak Flowrate
Rectangular Weir
Crest = Sharp
Bottom Length (ft) = 1.25
Total Depth (ft) = 0.25
Calculations
Weir Coeff. Cw = 3.33
Compute by: Known Q
Known Q (cfs) = 0.28
Highlighted
Depth (ft) = 0.17
Q (cfs) = 0.280
Area (sqft) = 0.21
Velocity (ft/s) = 1.36
Top Width (ft) = 1.25
0 .5 1 1.5 2 2.5
Depth (ft)Depth (ft)Weir @ Proposed Site 10YR Peak Flowrate
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.4/04/2019
Weir Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Mar 19 2019
Weir @ Proposed Site 100YR Peak Flowrate
Rectangular Weir
Crest = Sharp
Bottom Length (ft) = 1.25
Total Depth (ft) = 0.25
Calculations
Weir Coeff. Cw = 3.33
Compute by: Known Q
Known Q (cfs) = 0.49
Highlighted
Depth (ft) = 0.24
Q (cfs) = 0.490
Area (sqft) = 0.30
Velocity (ft/s) = 1.63
Top Width (ft) = 1.25
0 .5 1 1.5 2 2.5
Depth (ft)Depth (ft)Weir @ Proposed Site 100YR Peak Flowrate
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.4/04/2019
ASPEN CHARTS AND
FIGURES
4/04/2019
City of Aspen Urban Runoff Management Plan
Chapter 3 - Runoff 3-2 Rev 2/2010
Figure 3.1 Natural Resource Conservation Service (NRCS) Soil Map for Aspen
4/04/2019
City of Aspen Urban Runoff Management Plan
Chapter 3 - Runoff 3-6 Rev 10/2014
Figure 3.2 – Runoff Coefficients for NRCS Hydrologic Soil Group A
Figure 3.3 – Runoff Coefficients for NRCS Hydrologic Soil Group B
4/04/2019
City of Aspen Urban Runoff Management Plan
Chapter 2 - Rainfall 2-2 Rev 9/2014
into thunderstorms. Autumn in Aspen is usually dry and warm and during September daytime temperatures
can reach 70°F, but night temperatures can drop to freezing. Aspen is renowned for its warm winter sun.
Winter daytime temperatures typically range from 20 to 40°F in the City and from 10 to 30°F on the
mountain. Once the sun goes down, the temperature drops dramatically. Table 2.1 presents monthly
statistics for temperature, precipitation, snowfall, and snow depth in the Aspen area.
Table 2.1 Monthly Statistics for Temperature and Precipitation in Aspen
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
Average Max. Temperature (F) 35 39 45 52 63 72 78 76 69 58 43 35 55.5
Average Min. Temperature (F) 9.1 12 20 26 35 41 47 46 39 30 19 9.7 27.7
Average Total Precipitation (in.) 1.7 2.1 2.7 2.5 2.1 1.4 1.8 1.6 2.1 2 2.6 1.9 24.37
Average Total Snowfall (in.) 25 27 28 20 7.8 1 0 0 1 11 28 25 173.8
Average Snow Depth (in.) 21 28 27 12 1 0 0 0 0 1 6 14
(Source: Station 050372 at Aspen 1 SW, Colorado)
2.3 Rainfall Depth, Duration, Frequency, and Intensity
The rainfall intensity-duration-frequency (IDF) curve is a statistical formula to describe the relationship
among the local rainfall characteristics and return periods. The IDF curve is used in the Rational Method
for peak runoff predictions of basins smaller than 90 acres. Based on the NOAA Atlas Volume 3, the
IDF curve for the City of Aspen can be derived according to the locality and elevation. The City of Aspen is
located at approximately 39°11′32″N and 106°49′28″W, at an elevation of approximately 8,100 feet.
Based on depth and duration data (Appendix B, Table 1), rainfall intensities can be calculated for various
frequencies. Rainfall intensity data, which form the basis of the Intensity-Duration-Frequency (IDF) curves
in Figure 2.1 are provided in Table 2.2.
Table 2.2 Rainfall Intensity-Duration-Frequency in Aspen, Colorado
Return Rainfall Intensity in inch/hr for Various Periods of Duration
Period 5-min 10-min 15-min 30-min 1-hr (P1) 2-hr 3-hr 6-hr 24-hr
2‐yr 2.06 1.51 1.23 0.77 0.47 0.28 0.21 0.13 0.06
5-yr 2.98 2.17 1.77 1.09 0.64 0.36 0.26 0.16 0.07
10-yr 3.72 2.72 2.22 1.35 0.77 0.43 0.30 0.18 0.08
25‐yr 4.75 3.47 2.82 1.71 0.95 0.53 0.36 0.21 0.09
50‐yr 5.53 4.05 3.30 1.98 1.09 0.60 0.41 0.24 0.11
100-yr 6.32 4.63 3.76 2.24 1.23 0.67 0.45 0.26 0.12
Using the data in Table 2.2 (derived from NOAA Atlas 14 Volume 8), the following equation was derived
that can be used to determine intensities not shown in the IDF table or curve:
052.1
1
)10(
8.88
dT
PI (Equation 2-1)
Where, I = rainfall intensity (inch/hr),
P1 = 1-hr rainfall depth (inches), and
Td = duration or time of concentration (minutes).
4/04/2019
City of Aspen Urban Runoff Management Plan
Chapter 2 - Rainfall 2-4 Rev 9/2014
Note: Accuracy is more reliable at 5 minute increments.
Figure 2.1 IDF Curves for Aspen, Colorado
0
1
2
3
4
5
6
7
0 5 10 15 20 25 30 35 40 45 50 55 60
In
t
e
n
s
i
t
y
(i
n
c
h
/
h
r
)
Duration in Minutes
Rainfall IDF for Aspen, Colorado
2‐yr 5‐yr 10‐yr 25‐yr 50‐yr 100‐yr
4/04/2019
City of Aspen Urban Runoff Management Plan
Chapter 8 – Water Quality 8-33 Rev 8/2009
Figure 8.13 Aspen Water Quality Capture Volume
4/04/2019