HomeMy WebLinkAboutFile Documents.837 W Smuggler St.0240.2018 (22).ARBK
DRAINAGE REPORT
FOR
RANGER STATION SUBDIVISION
Lot 1
837 West Smuggler Street
CITY OF ASPEN, COLORADO
PARCEL ID: 2735-124-28-001
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
September 21, 2018
Revised: December 18, 2018
HCE JOB NUMBER: 2181030.01
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TABLE OF CONTENTS
SECTION PAGE
I. GENERAL LOCATION AND DESCRIPTION OF SITE 4
II. DRAINAGE STUDIES 5
III. EXISTING SUB BASIN DESCRIPTION 6
IV. DRAINAGE DESIGN CRITERIA 7
V. DRAINAGE FACILITY DESIGN 9
VI. CONCLUSION 13
VIII. REFERENCES 13
EXHIBITS:
1. Vicinity Map (8.5”x11”)
2. Flow Path (8.5”x11”)
3. Existing Drainage Basin Map (11”x17”)
4. Proposed Drainage Basin Map (11”x17”)
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
Valleypan & Swale & Pipe Calculations
100-year Detention
Drywell-WQCV-Detention
Weir Calculation
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
05/28/2019
Reviewed by Engineering
06/03/2019 4:28:07 PM
"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.
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I. GENERAL LOCATION AND DESCRIPTION OF SITE
A. Location
Lot 1 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 easterly of this property along a slight rise. North 8th
Street is on west side of the property 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 837 W. Smuggler in the Ranger Station Subdivision site is
approximately 6,623 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 are bound by Lot 4 to the south and Lot 2 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 west sides are bound by roadways and vegetation. The
existing site consists of vegetation, and utility pedestals and the alley under construction.
There are multiple trees on the site per the survey conducted by HCE and Sopris Engineering.
These existing trees have been noted within the proposed site development plan and a tree
removal permit from the architect/owner. The remaining trees on the site, 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 areas to the northwest. Eastern and
southern flows enter the site from the adjacent lots. Most of the flow from the south is
intercepted by the new alley and discharges into a new drywell or is directed to the swale
along N. 8th St. Flows from the east will be intercepted by Lot 2 and after flowing through the
storm-water system on that lot will discharge northerly into the W. Smuggler ROW as it has
historically. This includes the basin to the south one basin on the easterly side of the site and
one basin on the westerly side of the site. The main historic release for this site is the
northwest corner and the flows convey offsite as 100 year overflow from a pond and drywell
system. This site is located on the boundary of the Castle Creek and Aspen Mountain
drainage basins; therefore, no significant offsite basins were used in the design. The historic
drainage of the site was delineated into three basins; see attached existing basin map for site
layout (EXDR-01).
C. Lot Soils Description
A site-specific geotechnical soil study has been completed for this site for foundation design
and a percolation test for Lot 3 were provided (Exhibit #7). The site is well above the river
elevation and groundwater in not anticipated at the depth of our drywell. The City of Aspen
soils map locates this site in the Type “B” soils area. According to the USDA Web Soil
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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 some basement sections 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 on the northwest corner. Site landscaping will include
grass swales around the home and a significant amount of grasses, trees and shrubs 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 portion of this lot in the new alley contains a portion of the drywell and the detention for
the alley improvements. The alley was reviewed through the city process with the alley
approval and the alley and detention system acts independently of the new home being
proposed.
The proposed home’s drainage will be mitigated by providing site detention and water quality
within the site through a network of grass-lined swales, detention pond and drywell. The
drywell will collect the required WQCV per the city code at a factor of 1.5 times the required
volume. The drywell and pond will collect the detention volume and will discharge to
groundwater 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 concrete
weir. The site is required to capture 75.3CF of WQCV. The site is also required to capture
167.5CF of detention, thus sizing the drywell and pond based upon the FAA Method to
calculate the time of concentration with a controlled release to match historic rates. The 4’
diameter and 10’ deep drywell can accommodate a total of 172.1CF, including an upper
chamber capable of 86CF; see attached WQCV and detention drywell calculations in the
Appendices. The proposed pond has 3:1 side slopes and a depth of roughly 0.42’ adding an
additional 29CF of detention; 201.1CF in total.
The site consists of three proposed basins, see attached proposed basin map for site layout
(Exhibit #4).
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.
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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 to West Smuggler along with this site and down Nth. 8th as
before. This system ultimately delivers the stormwater to 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 one onsite drainage basin. Refer to sheet EXDR (exhibit #3)
for a map of existing basin layouts. Basin EX-1 encompasses the entire access road.
Historic Flow Path One:
Runoff from basin EX-1 sheet flows to the north on the easterly side of the property across the
site from a high point in the southeast portion of the site. The runoff continues to sheet flow
past the property boundary into an existing roadside swale before crossing Smuggler Street at
the intersection of N. 8th and 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:
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Runoff from basin EX-2 sheet flows to the north on the westerly side of the property across
the site from a high point in the southeast portion of the site. The runoff continues to sheet
flow past the property boundary into an existing roadside swale before crossing Smuggler
Street at the intersection of N. 8th and 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 Three:
Runoff from basin EX-3 sheet flows to the west in the proposed alley corridor and then
northerly in the n. 8th Street swale. The runoff continues to sheet flow past the property
boundary before crossing Smuggler Street at the intersection of N. 8th and 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.
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 0.095 0.15 2.83 0.04 0.35 4.53 0.15
EX-2 0.037 0.15 3.07 0.02 0.35 4.90 0.06
EX-3 0.02 0.15 2.87 0.01 0.35 4.58 0.03
TOTAL 0.07 TOTAL 0.24
Existing historic release rates from the site release at Design Point 1 is at a rate of 0.06cfs
(10yr) and 0.22cfs (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 requires 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
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space) per the URMP.
Water Quality Capture Volume (WQCV) will be determined for the site as per the URMP
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 bioretention 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.
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
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The capacity of the valley pan within the driveway is calculated utilizing the Hydrology
channel calculator with AutoCAD’s system. The valley pan has the ability to carry the entire
basin design flows even though only a portion of the basin will flow through the pan. There
are also a couple of pipes, within the system, that carry the stormwater flows into the pond
drywell area. Pipes have been sized per Civil 3D Hydraflow Express utilizing Manning’s
equation. The 6” pipe is located under the sidewalk going out to W. Smuggler and the 4” pipe
is located from the deck drains that will discharge through the building and directly to the
drywell; during a 100yr storm, the pipe capacities are 38% and 18% respectively. See basin
descriptions below for explanation.
WQCV and required detention volumes will be captured in the underground drywell and
percolate into the silty sandy gravel/cobble underneath and around the drywell. The drywell
has been designed to accommodate a total of 172.1CF, including an upper chamber capable of
86CF. The drywell meets the total required detention of 167.5 CF, which also covers the
75.3CF of WQCV per the 1.5 factor calculated against the overall site requirements. This
leaves approximately 4.6 CF for excess capacity, not including the extra storage volume
provided by the pond. The drywell and pond will collect storm water from the site via pipes
and swales. This water conveys to the pond and drywell via the swale flowlines and through
patio drain piping with minimum slopes of 2.2% 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 123SF that exceeds the
required 96SF. 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, 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
nearby Lot 3.
If the drywell and pond water level surpasses the proposed detention, then the system will
overflow via a broad crested concrete weir, 5.5’x0.67’ with a depth of 0.25’. This will allow
storm-water to leave the site at the historic 10-year and 100-year rates; 0.06 CFS and 0.22
CFS. See appendices for weir release calculations.
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 are standard zoning
setbacks from property lines. These setbacks do not affect the overall site drainage design.
V. DRAINAGE FACILITY DESIGN.
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A. General Concept
The proposed site plan calls for a new single family home, concrete driveway and sidewalks,
drainage facilities, and associated landscaping. A drywell and pond are proposed to be
constructed on the northeast side of the property. The pond and drywell will allow for the
capture of the required WQCV and detention per the URMP code. A sidewalk and ADA
compliant ramp along the east side of 8th Street constructed with the alley permit will give
access to pedestrians. The existing swale along 8th Street will carry flow to the corner of
Smuggler Street and 8th. The only change to the stormwater released from the site will be that
less runoff will sheet flow to the northwest down N. 8th due to full detention of the area of the
lot in the alley. This will improve the neighboring properties stormwater situation.
Historically, a total rate of 0.06cfs left the site as sheet flow to the northwest. In the proposed
condition, no more than a total of 0.22cfs through the proposed weir. First the flows will go
to the pond and drywell with the excess capacity before flowing 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 site constraints, this is the most feasible design for the
site. The grass lined swales will allow for capture of all hardscape water and the transfer of
that water to the pond and drywell with the WQCV and required detention on the site. The
infiltration drywell size holds the WQCV based on the 1.5 factor and the detention required
for drywells per code. A site-specific geotechnical soil study has been completed for this site,
with gradation of the soils and we are utilizing a percolation test for Lot 3 less than 75’ away
and is 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 but
per the Geotechnical engineer we are only having the perforations once the depth is beneath
the footer elevations. The basement is located much further back well over 10’ away from
the drywell. With the site constraints, the use of swales and the pond to store and convey the
stormwater all allows for a 10’ 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 to provide treatment before entering the pond and drywell. Over detention also
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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 drywell being oversized will reduce small storm runoff from the site and
will accommodate for 10yr or 100yr storm events. The drywell 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 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. Refer to sheet PRDR, Exhibit
#4, in the exhibit section for a map of the proposed basins and drainage design.
Basin PR-1 consists of the westerly side of the lot and approximately half of the proposed
home. This basin also includes the driveway and sidewalks on the front and back of the
home. Additionally the drywell and the pond to the north of the lot are 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 and into the drywell. The driveway in at the rear of the
property conveys stormwater via a pan between the alley and the garage. The flows release at
design point 1.
Basin PR-2 consists of the easterly side of the lot and approximately half of the proposed
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home. This basin also includes a pipe from an upper deck that will drain to the drywell.
There are also some ac pads and a small patio included within this basin. 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 2.
Basin PR-3 consists of the alley that has been designed and is currently being completed with
the permit for the alley improvements. This basin has a drywell that is designed to detain the
entire storm event for the PR-3 basin. The flows release at design point 3 into N. 8th.
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 0.068 0.44 3.96 0.12 0.53 6.33 0.23
PR-2 0.07 0.41 3.96 0.11 0.52 6.33 0.23
PR-3 0.014 0.92 3.96 0.05 0.96 6.33 0.08
TOTAL 0.28 TOTAL 0.54
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 drywell, thus reducing the transfer of pollutants to the City
of Aspen storm sewer system and the 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 being utilized for the WQCV is capable of capturing the 86CF of
Volume.
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Table 3. Proposed WQCV Table
BASIN
AREA
(S.F.)
IMPERVIOUS
AREA (SF)
PERCENT
IMPERVIOUS
WQCV (Watershed
inches)
WQCV
(CF)
PR-1 2983 1677 56.2 0.11 27.3
PR-2 3043 1586 52.1 0.1 25.4
TOTAL 6026 3263 54.2 50.2
x1.5 FACTOR 75.3
D. Operation and Maintenance
Correct operation of the system shall include drainage flowing north along both swales,
draining to the pond and into the drywell. Once the drywell overtops and the pond reaches
capacity, the system will overflow via a concrete weir to allow storm-water to leave the
northwest corner of the site at historic rates. Grass swales, pond, valley pan and drywell shall
all be kept clear of debris for site inspections. If the system is not functioning the pond will
not be draining and the drywell will need to be cleaned. See below for drywell function.
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
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 drywell 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.
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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.
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 Kumar, Inc. “Subsoil Study for Foundation Design, Proposed Residence, Lot 1, Ranger
Station Subdivision, Southeast Corner of West Smuggler Street and 8th Street, Aspen, CO”
dated August 22, 2018, Job Number 18-7-507.
UDFCD. www.udfcd.org.
05/28/2019
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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
05/28/2019
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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
05/28/2019
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Exhibit #7 – Subsoil Study and Percolation Test
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05/28/2019
HYDROLOGIC
COMPUTATIONS
05/28/2019
EXISTING CONDITIONS
05/28/2019
Lot 1, Ranger Station Subdivision
DRAINAGE REPORT
BY: BDB
CHECKED BY: RDN
DATE: 10-1-18
EX-1 4,134.7 0.095 0.0 0.0 0.08 0.15 0.35
EX-2 1,626.1 0.037 0.0 0.0 0.08 0.15 0.35
EX-3 867.4 0.020 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)
05/28/2019
Ranger Station Subdivision, Aspen
DRAINAGE REPORT
BY: BDB
CHECKED BY: RDN
DATE: 10-1-18
REACH
Basin I P1-10yr P1-100yr Td
EX-1 2.83 0.77 10.6
EX-1 4.53 1.23 10.6
Basin I P1-10yr P1-100yr Td
EX-2 3.07 0.77 9.1
Tc EX-2 4.90 1.23 9.1
TC
Tc
Basin I P1-10yr P1-100yr Td
10 YEAR EX-3 2.87 0.77 10.4
100 YEAR EX-3 4.58 1.23 10.4
To = [0.395 (1.1 - C5) SQRT(L)] / (S0.333) 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
EX-2
3.07
4.90
Rainfall Intenstity Chart EX-2
0.0000
1
0.0
9.1
10.3
6.0
EX-2
0.08
52.9
0.032
9.1
0
4.58
EX-3
0.08
67
Rainfall Intenstity Chart EX-3
15.1
10.4
5.0
EX-3
2.87
0.01
15.1
0
0.0000
1
0.0TR
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
4.53
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
2.83
5.0
1
RATIONAL COEFFICIENT. C (FIGURE 3.2 OF URMP)
Rainfall Intenstity Chart EX-1
0.027
14.0
EX-1
111
0.08
10.6
MINIMUM 5 MINUTES
14.0
EX-1BASIN
(MIN)
05/28/2019
CALCULATED BY: BDB STANDARD FORM SF-3
DATE: 10-1-18 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 30.020 0.15 10.4 0.00 2.872 EX-3 0.01
DESIGN POINT 12.830.095
REMARKS
CHANNEL
EX-11 10.60.15 0.01 0.04
DE
S
I
G
N
P
O
I
N
T
DIRECT RUNOFF
STRUCTURE NO.
TOTAL RUNOFF
PROJECT: LOT 1 RANGER STA. SUBDIVISION
JOB NO. 2181030.01
PIPE
DESIGN STORM: EXISTING 10 YEAR
TRAVEL TIME
2 EX-2 0.037 0.15 9.1 DESIGN POINT 20.01 3.07 0.02
05/28/2019
CALCULATED BY: BDB STANDARD FORM SF-3
DATE: 9-13-18 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
(
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)
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 4.58 0.032 EX-3 0.020 0.35 10.4
0.15 DESIGN POINT 1
TRAVEL TIME
REMARKS
1 EX-1 0.095 0.35 10.6 0.03 4.53
JOB NO. 2181030.01
PROJECT: LOT 1 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
2 EX-2 0.037 0.35 9.1 DESIGN POINT 20.01 4.90 0.06
05/28/2019
PROPOSED CONDITIONS
05/28/2019
Ranger Station Subdivision, Aspen
DRAINAGE REPORT
BY: BDB
CHECKED BY: RDN
DATE: 10-1-18
PR-1 2,983.2 0.068 1,677.3 56.2 0.110 27.3 0.34 0.38 0.44 0.53
PR-2 3,043.1 0.070 1,586.0 52.1 0.100 25.4 0.30 0.35 0.41 0.52
PR-3 600.6 0.014 600.6 100.0 0.260 13.0 0.89 0.90 0.92 0.96
TOTAL SITE 6,026.3 0.138 3,263.3 54.2 0.1 50.2
Time 1.5 for Drywell 75.3
BASIN AREA (S.F.) AREA (ACRE)
IMPERVIOUS AREA
(SF)
PERCENT
IMPERVIOUS
2 YR RUNOFF
COEFFICIENT
10 YR RUNOFF
COEFFICIENT
100 YR RUNOFF
COEFFICIENT
WQCV (Watershed
inches) WQCV (CF)
5 YR RUNOFF
COEFFICIENT
Type B Soils
05/28/2019
Ranger Station Subdivision, Aspen
DRAINAGE REPORT
BY: BDB
CHECKED BY: RDN
DATE: 10-1-18
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-1 2.42 0.47 5.0
TC PR-1 3.96 0.77 5.0
Tc PR-1 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-1 2.42 0.47 5.0
PR-1 3.96 0.77 5.0
To = [0.395 (1.1 - C5) SQRT(L)] / (S0.333) EQUATION 3-4 PR-1 6.33 1.23 5.0
C= 5 YR runoff coefficient from City of Aspen Urban Runoff Management Plan
INTENSITY I=29p/((10+T)^0.789) EQUATION 2-1
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
Rainfall Intenstity Chart PR-2
Rainfall Intenstity Chart PR-3
5.0
PR-3
2.42
3.96
6.33
49.1
0.03
3.46
0.2
1.2
10.3
PR-2
2.42
3.96
6.33
PR-3
0.900
10.0
0.02
0.9
0.037
2.55
0.6
3.2
10.6
5.0
PR-2
0.350
10.0
0.05
2.5
97.0
URBAN CHECK = 10+L/180
142.6
0.026
10.9
To (MIN)
5.0
2.6
3.3
4.2
0.9
RATIONAL COEFFICIENT. C (FIGURE 3.2 OF URMP) 0.380
AREA IDENTIFIER
FLOW SLOPE, S (ft./ft.)
(MIN)
TRAVEL TIME = L/(60V) (min.)
0.03
BASIN
MINIMUM 5 MINUTES
6.33
PR-1
3.96
2.42
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
12.6
05/28/2019
CALCULATED BY: BDB STANDARD FORM SF-3
DATE: 10-1-18 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
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M
I
N
)
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M
(
C
*
A
)
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C
)
I
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H
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)
Q
(
C
F
S
)
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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
(
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)
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P
E
S
I
Z
E
(
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N
C
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S
)
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N
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T
H
(
F
T
)
VE
L
O
C
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T
Y
(
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P
S
)
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(
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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 3
Design Point 2
3 PR-3 0.014 0.89 5.00 0.01 2.42
0.02 2.42 0.052 PR-2 0.070 0.30 5.00
TRAVEL TIMEPIPESTREETTOTAL RUNOFF
PROJECT: LOT 1 RANGER STA. SUBDIVISION
JOB NO. 2181030.01
DIRECT RUNOFF
0.06
STRUCTURE NO.
DE
S
I
G
N
P
O
I
N
T
REMARKS
DESIGN STORM: PROPOSED 2 YEAR
0.34 Design Point 11 PR-1 5.000.068 0.02 2.42
05/28/2019
CALCULATED BY: BDB STANDARD FORM SF-3
DATE: 10-1-18 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
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H
R
)
Q
(
C
F
S
)
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(
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I
N
)
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M
(
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*
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)
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C
)
I
(
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Q
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F
S
)
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O
P
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(
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)
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R
E
E
T
F
L
O
W
(
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F
S
)
DE
S
I
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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)
JOB NO. 2181030.01
PROJECT: LOT 1 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 TRAVEL TIME
REMARKS
1 PR-1 0.068 0.44 5.00 0.03 3.96 0.12 Design Point 1
2 PR-2 0.070 0.41 5.00 0.03 3.96 0.11 Design Point 2
3 PR-3 0.014 0.92 5.00 0.01 3.96 0.05 Design Point 3
05/28/2019
CALCULATED BY: BDB STANDARD FORM SF-3
DATE: 10-1-18 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
(
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I
N
)
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M
(
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*
A
)
(
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C
)
I
(
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N
/
H
R
)
Q
(
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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
)
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N
G
T
H
(
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T
)
VE
L
O
C
I
T
Y
(
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P
S
)
Tt
(
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I
N
)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)
JOB NO. 2181030.01
PROJECT: RANGER STATION SUBDIVISION
DESIGN STORM: PROPOSED 100 YEAR
STRUCTURE NO.
DE
S
I
G
N
P
O
I
N
T
DIRECT RUNOFF TOTAL RUNOFF STREET PIPE TRAVEL TIME
REMARKS
1 PR-1 0.068 0.53 5.00 0.04 6.33 0.23 Design Point 1
2 PR-2 0.070 0.52 5.00 0.04 6.33 0.23 Design Point 2
3 PR-3 0.014 0.96 5.00 0.01 6.33 0.08 Design Point 3
05/28/2019
HYDRAULIC
COMPUTATIONS
05/28/2019
VALLEY PAN & SWALE & PIPE CALCULATIONS
05/28/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Friday, Sep 21 2018
PR-1 Swale 10-year Flowrate
Triangular
Side Slopes (z:1) = 2.00, 2.00
Total Depth (ft) = 0.50
Invert Elev (ft) = 7896.51
Slope (%) = 2.18
N-Value = 0.027
Calculations
Compute by: Known Q
Known Q (cfs) = 0.12
Highlighted
Depth (ft) = 0.20
Q (cfs) = 0.120
Area (sqft) = 0.08
Velocity (ft/s) = 1.50
Wetted Perim (ft) = 0.89
Crit Depth, Yc (ft) = 0.19
Top Width (ft) = 0.80
EGL (ft) = 0.23
0 .5 1 1.5 2 2.5 3
Elev (ft)Depth (ft)Section
7896.00 -0.51
7896.50 -0.01
7897.00 0.49
7897.50 0.99
7898.00 1.49
Reach (ft)
05/28/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Friday, Sep 21 2018
PR-1 Swale 100-year Flowrate
Triangular
Side Slopes (z:1) = 2.00, 2.00
Total Depth (ft) = 0.50
Invert Elev (ft) = 7896.51
Slope (%) = 2.18
N-Value = 0.027
Calculations
Compute by: Known Q
Known Q (cfs) = 0.23
Highlighted
Depth (ft) = 0.25
Q (cfs) = 0.230
Area (sqft) = 0.13
Velocity (ft/s) = 1.84
Wetted Perim (ft) = 1.12
Crit Depth, Yc (ft) = 0.25
Top Width (ft) = 1.00
EGL (ft) = 0.30
0 .5 1 1.5 2 2.5 3
Elev (ft)Depth (ft)Section
7896.00 -0.51
7896.50 -0.01
7897.00 0.49
7897.50 0.99
7898.00 1.49
Reach (ft)
05/28/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Saturday, Sep 22 2018
PR-2 Swale 10-year Flowrate
Triangular
Side Slopes (z:1) = 4.00, 4.00
Total Depth (ft) = 0.70
Invert Elev (ft) = 7896.51
Slope (%) = 2.34
N-Value = 0.027
Calculations
Compute by: Known Q
Known Q (cfs) = 0.11
Highlighted
Depth (ft) = 0.15
Q (cfs) = 0.110
Area (sqft) = 0.09
Velocity (ft/s) = 1.22
Wetted Perim (ft) = 1.24
Crit Depth, Yc (ft) = 0.14
Top Width (ft) = 1.20
EGL (ft) = 0.17
0 1 2 3 4 5 6 7 8
Elev (ft)Depth (ft)Section
7896.00 -0.51
7896.50 -0.01
7897.00 0.49
7897.50 0.99
7898.00 1.49
Reach (ft)
05/28/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Saturday, Sep 22 2018
PR-2 Swale 100-year Flowrate
Triangular
Side Slopes (z:1) = 4.00, 4.00
Total Depth (ft) = 0.70
Invert Elev (ft) = 7896.51
Slope (%) = 2.34
N-Value = 0.027
Calculations
Compute by: Known Q
Known Q (cfs) = 0.23
Highlighted
Depth (ft) = 0.19
Q (cfs) = 0.230
Area (sqft) = 0.14
Velocity (ft/s) = 1.59
Wetted Perim (ft) = 1.57
Crit Depth, Yc (ft) = 0.19
Top Width (ft) = 1.52
EGL (ft) = 0.23
0 1 2 3 4 5 6 7 8
Elev (ft)Depth (ft)Section
7896.00 -0.51
7896.50 -0.01
7897.00 0.49
7897.50 0.99
7898.00 1.49
Reach (ft)
05/28/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Friday, Sep 21 2018
Valley Pan @ 10.9% of PR-1 10-year Flowrate
Triangular
Side Slopes (z:1) = 8.00, 8.00
Total Depth (ft) = 0.13
Invert Elev (ft) = 7898.46
Slope (%) = 3.00
N-Value = 0.011
Calculations
Compute by: Known Q
Known Q (cfs) = 0.01
Highlighted
Depth (ft) = 0.04
Q (cfs) = 0.013
Area (sqft) = 0.01
Velocity (ft/s) = 1.02
Wetted Perim (ft) = 0.64
Crit Depth, Yc (ft) = 0.05
Top Width (ft) = 0.64
EGL (ft) = 0.06
0 .5 1 1.5 2 2.5 3 3.5
Elev (ft)Depth (ft)Section
7898.00 -0.46
7898.25 -0.21
7898.50 0.04
7898.75 0.29
7899.00 0.54
Reach (ft)
05/28/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Friday, Sep 21 2018
Valley Pan @ 10.9% of PR-1 100-year Flowrate
Triangular
Side Slopes (z:1) = 8.00, 8.00
Total Depth (ft) = 0.13
Invert Elev (ft) = 7898.46
Slope (%) = 3.00
N-Value = 0.011
Calculations
Compute by: Known Q
Known Q (cfs) = 0.03
Highlighted
Depth (ft) = 0.05
Q (cfs) = 0.030
Area (sqft) = 0.02
Velocity (ft/s) = 1.50
Wetted Perim (ft) = 0.81
Crit Depth, Yc (ft) = 0.07
Top Width (ft) = 0.80
EGL (ft) = 0.08
0 .5 1 1.5 2 2.5 3 3.5
Elev (ft)Depth (ft)Section
7898.00 -0.46
7898.25 -0.21
7898.50 0.04
7898.75 0.29
7899.00 0.54
Reach (ft)
05/28/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Saturday, Sep 22 2018
6IN PIPE AT PR-1 10-YEAR FLOWRATE
Circular
Diameter (ft) = 0.50
Invert Elev (ft) = 7895.47
Slope (%)= 1.00
N-Value = 0.009
Calculations
Compute by:Known Q
Known Q (cfs) = 0.12
Highlighted
Depth (ft)= 0.13
Q (cfs)= 0.120
Area (sqft)= 0.04
Velocity (ft/s)= 2.92
Wetted Perim (ft) = 0.54
Crit Depth, Yc (ft) = 0.18
Top Width (ft)= 0.44
EGL (ft)= 0.26
0 1
Elev (ft)
7895.00
7895.25
7895.50
7895.75
7896.00
05/28/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Saturday, Sep 22 2018
6IN PIPE AT PR-1 100-YEAR FLOWRATE
Circular
Diameter (ft) = 0.50
Invert Elev (ft) = 7895.47
Slope (%) = 1.00
N-Value = 0.009
Calculations
Compute by: Known Q
Known Q (cfs) = 0.23
Highlighted
Depth (ft) = 0.19
Q (cfs) = 0.230
Area (sqft) = 0.07
Velocity (ft/s) = 3.35
Wetted Perim (ft) = 0.66
Crit Depth, Yc (ft) = 0.24
Top Width (ft) = 0.49
EGL (ft) = 0.36
0 1
Elev (ft)
7895.00
7895.25
7895.50
7895.75
7896.00
05/28/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Friday, Sep 21 2018
4in Deck Drain Pipe at 7.7% of PR-2 10yr Flowrate
Circular
Diameter (ft) = 0.33
Invert Elev (ft) = 7892.63
Slope (%) = 2.00
N-Value = 0.009
Calculations
Compute by: Known Q
Known Q (cfs) = 0.01
Highlighted
Depth (ft) = 0.04
Q (cfs) = 0.008
Area (sqft) = 0.01
Velocity (ft/s) = 1.34
Wetted Perim (ft) = 0.24
Crit Depth, Yc (ft) = 0.05
Top Width (ft) = 0.22
EGL (ft) = 0.07
0 1
Elev (ft)
7892.00
7892.25
7892.50
7892.75
7893.00
05/28/2019
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Friday, Sep 21 2018
4in Deck Drain Pipe at 7.7% of PR-2 100yr Flowrate
Circular
Diameter (ft) = 0.33
Invert Elev (ft) = 7892.63
Slope (%) = 2.00
N-Value = 0.009
Calculations
Compute by: Known Q
Known Q (cfs) = 0.02
Highlighted
Depth (ft) = 0.06
Q (cfs) = 0.020
Area (sqft) = 0.01
Velocity (ft/s) = 1.86
Wetted Perim (ft) = 0.29
Crit Depth, Yc (ft) = 0.08
Top Width (ft) = 0.26
EGL (ft) = 0.11
0 1
Elev (ft)
7892.00
7892.25
7892.50
7892.75
7893.00
05/28/2019
Hydrology Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Thursday, Sep 20 2018
<Name>
Hydrograph type = Rational Peak discharge (cfs) = 0.373
Storm frequency (yrs) = 100 Time interval (min) = 1
Drainage area (ac) = 0.140 Runoff coeff. (C) = 0.54
Rainfall Inten (in/hr) = 4.931 Tc by FAA (min) = 9
IDF Curve = AspenIDFcurve.IDF Rec limb factor = 1.00
Hydrograph Volume = 201 (cuft); 0.005 (acft)
0 5 10 15 20
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 = 0.37 (cfs)Outflow Hyd *Req. Stor = 85 (cuft) *
* Estimated
Vol=(1/2)x(0.24cfs)x(12.5min)x(60s/1min)=82.5cf
New Req. Stor=(85+82.5) cuft=167.5 cuft
05/28/2019
FAA Formula Tc Worksheet
Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve
Rational
<Name>
Description
Flow length (ft) = 134.50
Watercourse slope (%) = 2.60
Runoff coefficient (C) = 0.54
Time of Conc. (min) = 9
05/28/2019
DETENTION VOLUME CALCULATIONS
05/28/2019
Volume to Width of Depth of gravel Dia of Percent Concrete Cylinder
Detain (cf) Gravel (ft) Below M.H. (ft) M.H. Voids (%) Thickness (in)
85.0 1.5 1 4 30 5
Area of M.H. (sqft) 12.6
Area of Gravel (sqft) 29.8 (1.23in/12in)*3125sf 241.4583333
Area of Concrete Cylinder (sqft) 5.78
Volume of 6" PCC Slab (sqft) 6.3
Volume of Gravel Bottom 48.2
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
(ft) (cf) (cf) (cf) (cf) (cf) (cf)
1 0.0 0.0 0.0 0.0 0.0 0.0 no
2 0.0 0.0 9.7 0.0 3.4 3.4 no
3 0.0 0.0 9.7 12.6 16.0 16.0 no
4 0.0 0.0 9.7 25.1 28.5 28.5 no
5 78.0 23.4 9.7 37.7 41.1 64.5 no
6 107.9 32.4 9.7 50.3 53.7 86.0 Meets Min. WQCV 75.3
7 137.7 41.3 9.7 62.8 66.2 107.6 Meets Min.
8 167.6 50.3 9.7 75.4 78.8 129.1 Meets Min.
9 197.4 59.2 9.7 88.0 91.4 150.6 Meets Min.
10 227.3 68.2 9.7 100.5 103.9 172.1 Meets Min. Provided Detention
11 257.1 77.1 9.7 113.1 116.5 193.6 Meets Min.
12 287.0 86.1 9.7 125.7 129.1 215.2 Meets Min.
13 316.8 95.0 9.7 138.2 141.6 236.7 Meets Min.
14 346.6 104.0 9.7 150.8 154.2 258.2 Meets Min.
Transmissivity Calc.
Depth of Gravel (ft)= 5
K from NRCS National Engineering Handbook, figure 3‐10, soil class GM
AP=(VR)/(K)(43,200)
AP=Total area of sides (sf)123.05
VR = runoff volume (cf)85.0
K= Hydraulic Conductivity (ft/s)0.000035
.
Area of Percolation Required (sf)56.22
Tele: (970) 945-8676 - Fax (970) 945-2555
Calculation of Drywell and Gravel
Variables
4' DIAMETER, 10' DEEP DRYWELL
1517 BLAKE AVENUE
Glenw ood Springs, CO 81601
V=1-hr (P1)*A(impervious)
Ranger Station Subdivisio n
DRAINAGE STUDY DRYWELL CALCULATION S
September 21, 2018 HCE #: 2181030.01 J:/sdskproj/21/1030.01/excel/wqcv drywell.xls
WQCV Drywell Calculations
05/28/2019
WEIR CALCULATIONS
05/28/2019
Weir Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Thursday, Dec 6 2018
Weir 10-Year
Rectangular Weir
Crest = Broad
Bottom Length (ft) = 1.00
Total Depth (ft) = 0.25
Calculations
Weir Coeff. Cw = 2.60
Compute by: Known Q
Known Q (cfs) = 0.12
Highlighted
Depth (ft) = 0.13
Q (cfs) = 0.120
Area (sqft) = 0.13
Velocity (ft/s) = 0.93
Top Width (ft) = 1.00
0 .25 .5 .75 1 1.25 1.5
Depth (ft)Depth (ft)Weir 10-Year
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.05/28/2019
Weir Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Thursday, Sep 20 2018
Weir at 100-Year Historic Release Flowrate
Rectangular Weir
Crest = Broad
Bottom Length (ft) = 1.00
Total Depth (ft) = 0.25
Calculations
Weir Coeff. Cw = 2.60
Compute by: Known Q
Known Q (cfs) = 0.22
Highlighted
Depth (ft) = 0.19
Q (cfs) = 0.220
Area (sqft) = 0.19
Velocity (ft/s) = 1.14
Top Width (ft) = 1.00
0 .25 .5 .75 1 1.25 1.5
Depth (ft)Depth (ft)Weir at 100-Year Historic Release Flowrate
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.05/28/2019
ASPEN CHARTS AND
FIGURES
05/28/2019
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
05/28/2019
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
05/28/2019
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).
05/28/2019
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
05/28/2019
City of Aspen Urban Runoff Management Plan
Chapter 8 – Water Quality 8-33 Rev 8/2009
Figure 8.13 Aspen Water Quality Capture Volume
05/28/2019