HomeMy WebLinkAboutFile Documents.617 W Bleeker St.0052-2022-BCHO (13)
617 West Bleeker
Drainage Report
June 21, 2022
Revised December 7, 2022
Prepared By:
Vince Tomczak, P.E.
Crystal River Civil, LLC
Carbondale, CO 81623
vince@crystalrivercivil.com
(970) 510-5312
12/16/2022
Reviewed by Engineering
01/18/2023 8:19:17 AM
"It should be known that this review shall not
relieve the applicant of their responsibility to
comply with the requirements of the City of
Aspen. The review and approval by the City is
offered only to assist the applicant's
understanding of the applicable Engineering
requirements." The issuance of a permit based
on construction documents and other data shall
not prevent the City of Aspen from requiring the
correction of errors in the construction
documents and other data.
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Table of Contents
1.0 General Information ........................................................................................................... 3
1.1 Existing Conditions ......................................................................................................... 3
1.2 Proposed Conditions ...................................................................................................... 4
1.3 Existing Drainage Studies .............................................................................................. 5
1.4 Drainage Impacts ........................................................................................................... 5
2.0 Drainage Basins and Subbasins ........................................................................................ 5
2.1 Onsite Drainage Basins .................................................................................................. 5
2.2 Onsite Drainage Subbasins ............................................................................................ 5
2.3 Offsite Drainage Basins .................................................................................................. 5
3.0 Low Impact Site Design ..................................................................................................... 6
3.1 Principles ........................................................................................................................ 6
4.0 Hydrologic Criteria .............................................................................................................. 7
4.1 Runoff Calculation Method ............................................................................................. 7
4.2 Basin Analysis ................................................................................................................ 7
4.3 Sub Basin Analysis ......................................................................................................... 8
4.4 Water Quality and Storage Requirements ...................................................................... 9
5.0 Hydraulic Criteria ................................................................................................................ 9
5.1 Inlets ............................................................................................................................... 9
5.2 Pipes ............................................................................................................................. 10
6.0 Proposed Facilities ........................................................................................................... 11
6.1 Drywells ........................................................................................................................ 11
7.0 Operation and Maintenance ............................................................................................. 11
7.1 Drywell .......................................................................................................................... 11
7.2 Inlets and Trench Drains .............................................................................................. 12
7.3 Pervious Pavers ........................................................................................................... 12
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1.0 General Information
1.1 Existing Conditions
The property being discussed in this drainage report is addressed at 617 West Bleeker, Aspen,
Colorado 81611. The site is located within the City of Aspen in the area known as the “West End”
near Main Street. It is documented as parcel # 273512444002 and is described as City and
Townsite of Aspen Block: 24 and Lot: D Through F. The site is located in the middle of the West
Bleeker block, between North 5th Street and North 6th Street, and is surrounded by other
residential developments.
617 West Bleeker Street Vicinity Map
The property is currently developed with a single-family residence and is surrounded by well-
established trees and landscaping features. Concrete walkways and an at-grade deck surround
the existing residence. The topography of the site is relatively flat, sloping from the south to the
north towards West Bleeker Street, with positive drainage away from the existing structure.
Parking for the residence is accessed from West Bleeker Street. The driveway is a short, concrete
pad with concrete walkways continuing to the residence.
The majority of the existing utility services are found in the backyard of the parcel at the southern
property line. This includes sanitary sewer, gas, electric, telephone and communications services.
An electric transformer is located at the southwest corner of the parcel within a City of Aspen
Electric Easement. Water service to the property is located to the north, with a tap under the West
Bleeker Street.
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A geotechnical investigation has been completed for the property by Kumar & Associates, Inc. on
September 27, 2019 with a report dated on October 17, 2019. One boring has been drilled at the
northeastern property corner within the existing concrete driveway. This boring was drilled to a
depth of 21 feet and reported three feet of sandy fill material below the concrete pavement and
aggregate section. Following the fill material there is a sand and gravel (SW-GM) material with
cobbles to the auger refusal depth at 21 feet. A copy of this geotechnical report can be found
within the permit submission package.
1.2 Proposed Conditions
The proposed conditions at 617 West Bleeker Street includes the construction of a large, single-
family residence. The project is considered a “Major Project” per Table 1.1. of the City of Aspen
Urban Runoff Management Plan (URMP). The parcel is zoned for residential use and will not
require a change in land use or zoning.
The residence includes a snowmelted concrete driveway accessing a garage off the southern
property line. This connects into the alley located between West Bleeker and Main Street,
accessed via North 5th or North 6th Street. The driveway will be just over twenty feet wide and only
32 feet long. Boulder retaining walls are utilized for driveway construction and to create a flatter
lawn area in the southern area of the parcel. No walls on the property exceed thirty inches in
height. The residence has a proposed a patio and front entry, as well as walkways up to the front
door and rear access. Concrete mechanical pads are proposed for mechanical equipment on the
east side of the structure.
As required for designated “Major Projects”, the site requires a stormwater design that meets the
requirements of the URMP. This includes conveyance of major flows as well as detention to
eliminate additional flow rates from the development. The Low Impact Design (LID) Principals
within the URMP were used as guidelines in the development of the proposed design. The roof
structure will collect runoff through roof drains and gutters with downspouts. The roof area will tie
into the surrounding storm system. Several inlets located around the residences will collect any
runoff from landscaped areas. The driveway runoff is collected through a trench drain located at
the garage entry. All runoff is conveyed to an onsite drywell located near the southern property
line within the footprint of the concrete driveway. Due to the site constraints, the drywell shall be
designed to fully detain all runoff from the impervious areas from the development, since there is
no overflow path available.
Service utilities for the parcel generally follow the existing utility layout. All existing services shall
be abandoned per the utility provider’s requirements. Water service will require a new 1.5” tap off
the water main under West Bleeker Street. A new saddle tap for the sanitary sewer service line
will be installed on the sanitary main under the southern alley. The existing electric transformer
on the parcel will service the residence. Alterations to the utility easement are proposed to be
updated to meet current clearance requirements on the sides and back as per City of Aspen
Electric Department. The new easement can be found on the civil drawings and will be recorded
on the as-built survey for close out. Communications and telephone services will utilize the
existing pedestals located near the southwestern property corner. A new gas service tap is
located under the alley. All meter locations will be strategically located in coordination with the
architect and mechanical designer.
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1.3 Existing Drainage Studies
Currently there are no known studies performed on or around the site. The project is not within a
mudflow area defined within the URMP.
1.4 Drainage Impacts
Given that the proposed project is capturing and treating all stormwater from impervious areas for
full detention, the project will not impact downstream properties, Right-Of-Ways, or Stormwater
systems.
2.0 Drainage Basins and Subbasins
2.1 Onsite Drainage Basins
The site has been analyzed as one drainage basin that contains the entirety of the proposed
development. The point of concentration for the basin will be the drywell located within the
driveway.
Basin 1 is proposed as 7,172 square feet that is 60% impervious. This area includes the proposed
roof structure, the driveway, the concrete mechanical pads, patios, and the impervious walkways
surrounding the residence. The basin is collected by downspouts from the roof structure, a trench
drain in the driveway, and several inlets surrounding the residence. All stormwater is conveyed to
Drywell A. Drywell A has been sized to have enough capacity for the full detention volume for the
impervious areas collected. It has a storage depth of 13 feet (15 feet rim to sump depth) and an
eight-foot perforated section.
2.2 Onsite Drainage Subbasins
To size all piping and inlets, sub basins were required to be analyzed for the site.
Within Basin 1, subbasins 1.1, 1.3 1.6, 1.8, and 1.9 are all areas of the roof structure that are
collected via gutter and downspout systems, which tie into the adjacent underground storm
conveyance system. Subbasins 1.2, 1.4, 1.5, 1.7, and 1.10 are all areas collected by inlets located
within landscaped and hardscaped areas. Subbasin 1.11 includes the driveway area and is
collected through a six-inch trench drain located at the garage tie in point.
A summary showing all sub basin characteristics and their peak discharges can be seen in section
4.2 of this report, and a basins sheet can be found on sheet C5 of the civil set.
2.3 Offsite Drainage Basins
No offsite drainage basins impact the proposed development. No offsite drainage analysis is
included within this report.
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3.0 Low Impact Site Design
Low Impact Development (LID) aims to mimic the natural pre-development hydrologic patterns.
The goal is to manage storm water as close to its source as is possible. This entire developed
site is proposed at 48% impervious, and the captured onsite basin is 60% impervious.
3.1 Principles
Principle 1: Consider storm water quality needs early in the design process.
The design team focused on stormwater management early in the design phase and prioritized a
feasible and sustainable solution for water quality needs.
Principle 2: Use the entire site when planning for storm water quality treatment.
Given minimal area on the site, a drywell was utilized. However, the stormwater layout was
designed in a way to minimize the impacts of the existing conditions, trees, and transitions into
existing grade.
Principle 3: Avoid unnecessary impervious area.
Pervious paver patios and sand set pavers will be utilized to promote infiltration into the ground
in areas where possible. Large landscaping areas are included in the design to promote pre-
treatment before entering the storm system.
Principle 4: Reduce runoff rates and volumes to more closely match natural conditions.
All runoff from impervious surfaces on the property is collected and conveyed to a drywell, which
have been sized for the full detention volume.
Principle 5: Integrate storm water quality management and flood control.
A drywell is proposed onsite, which is designed to capture and treat stormwater for the entire site.
The drywell has been designed to detain the full detention volume of a 100-year 1-hour storm
event, which will eliminate any flooding impacts in the area that would be generated from this site
being developed.
Principle 6: Develop storm water quality facilities that enhance the site, the community, and the
environment.
The proposed stormwater system is designed to be treated onsite and will reduce the runoff into
neighboring properties and the public Right-of-Way system. This will minimize impacts of
stormwater on neighboring residences from the existing residence. The design allows for more
than adequate drainage while having minimal visual impacts.
Principle 7: Use treatment train approach.
The design proposes patios to release into landscaping to allow treatment prior to entering the
storm system in multiple areas on the site. Sumps are proposed for the inlets in the pipe network
to ensure treatment throughout the system. The filtration system within the dual chamber drywell
allows for an additional treatment level prior to infiltration.
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Principle 8: Design sustainable facilities that can be safely maintained.
Inlets, piping, and the drywell will be vacuumed or flushed periodically, as specified in the
maintenance section of this drainage report, to maintain adequate flow as designed. The designed
system includes cleanouts at roof drain connections and downspouts, simplified collection
systems that minimize maintenance, and easy access to the whole system. The dual chamber
drywell minimizes clogging and allows for maintenance of the system for longevity.
Principle 9: Design and maintain facilities with public safety in mind.
The proposed design for driveway and walkways allows for adequate drainage and reduces ice
buildup and dangerous conditions. Walkways and stairways are pitched at recommended slopes
and within building code thresholds to allow for safe circulation within the property. Grading has
been kept to a minimum and retainage has been minimized. Transitions into existing conditions
are smooth and natural.
4.0 Hydrologic Criteria
4.1 Runoff Calculation Method
Calculations and analyses defined in Chapter 2 and Chapter 3 of the URMP were used to define
the runoff from the basins on the property. The property is classified as a “Sub-urban area not
served by public storm sewer.” Pre-developed and developed runoff rates were determined for
both the 10-year 1-hour and the 100-year 1-hour storm events for capacity designs as required
by this classification. The basins defined for the project can be seen on the basins sheet of the
civil set.
The peak discharge shown in this analysis uses the Rational Method, as described in section 3.4
of the URMP. This requires several variables to be determined, including values for intensity, the
runoff coefficient, and basin area. Using the rainfall depths from Table 2-2 and the basin time of
concentration in conjunction with Equation 2-1, the rainfall intensity for the basins can be
calculated. The rainfall intensity equation shown in the URMP is a direct correlation of the Aspen
area Intensity Duration Frequency Curve derived from the NOAA Atlas 14 database. As stated
within the URMP, the time of concentration can be no less than 5 minutes for the calculations to
be effective. Due to the size of the basins on the site, the time of concentration within the basins
is less than 5 minutes. The runoff coefficient for each basin was established using the percent
impervious of the basin and the soil type in conjunction with the most up-to-date values as
presented in the Mile High Flood District Drainage Design Values for the specified soil type in the
area. For this project, an NRCS Soil Classification of B was utilized.
4.2 Basin Analysis
The tables below summarize the calculations that were performed on the basins using the
methods described in Section 4.1 of this report.
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4.3 Sub Basin Analysis
In addition to determining the peak discharge from basins, the areas are then subdivided into sub
basins to calculate their peak discharges. This allows for verification that all pipes and intakes into
the proposed conveyance structures have capacity. The URMP requires all structures to have
capacity for a 100-year 1-hour storm event. Using the same procedure discussed in 2.1 of this
drainage report, the peak discharge of each sub basin was determined.
Below is a table summarizing the values required for the sub basin analysis. The offsite basins
were included in this as well as they were included in calculations.
Rainfall depth, P 1 (in)0.77 Soil Class B Intensity (in/hr)Discharge (ft3/Sec)Q=CIA t
Note: For basins with a flow length of less than 500 feet, a Time of Concentration is assumed at 5 minutes. These calculations are assuming a NRCS Hydrologic Soil Class B.
Rainfall depth values derived from NOAA Atlas 14 data. Intensity equation has been derived from the Aspen area NOAA Atlas 14 IDF Curve.
Predeveloped Conditions
Basin Total Area Impervious Area Percent Impervious C Value Time of Concentration Intensity Peak Discharge
(Name)At (ft2) Ai (ft2)Ai/At (%) Tc (min)I (in/hr)Qp (ft3/sec)
1 7171.71 0 0.00%0.040 5 3.96 0.03
Developed Conditions
Basin Total Area Impervious Area Percent Impervious C Value Time of Concentration Intensity Peak Discharge
(Name)At (ft2) Ai (ft2)Ai/At (%) Tc (min)I (in/hr)Qd (ft3/sec)
1 7171.71 4316.24 60.18%0.540 5 3.96 0.35
10-Year 1-Hour Onsite Peak Discharge CalculationsI=88.8P1(10 +Td)1.052
Rainfall depth, P 1 (in)1.23 Soil Class B Intensity (in/hr)Discharge (ft3/Sec)Q=CIA t
Note: For basins with a flow length of less than 500 feet, a Time of Concentration is assumed at 5 minutes. These calculations are assuming a NRCS Hydrologic Soil Class B.
Rainfall depth values derived from NOAA Atlas 14 data. Intensity equation has been derived from the Aspen area NOAA Atlas 14 IDF Curve.
Predeveloped Conditions
Basin Total Area Impervious Area Percent Impervious C Value Time of Concentration Intensity Peak Discharge
(Name)At (ft2) Ai (ft2)Ai/At (%) Tc (min)I (in/hr)Qp (ft3/sec)
1 7171.71 0 0.00%0.430 5 6.33 0.45
Developed Conditions
Basin Total Area Impervious Area Percent Impervious C Value Time of Concentration Intensity Peak Discharge
(Name)At (ft2) Ai (ft2)Ai/At (%) Tc (min)I (in/hr)Qd (ft3/sec)
1 7171.71 4316.24 60.18%0.710 5 6.33 0.74
100-Year 1-Hour Onsite Peak Discharge CalculationsI=88.8P1(10 +Td)1.052
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4.4 Water Quality and Storage Requirements
For a property classified as a “Sub-urban area not served by public storm sewer”, runoff from the
site must meet the predeveloped peak discharge of a 100-year 1-hour storm event. Full detention
volume is detained on site due to the lack of an overflow path available on the property. All
equations used in the spreadsheets are directly from the URMP. A full detention analysis of the
drainage basin has been completed. The full detention volume is calculated using the impervious
area on the site and multiplying by the 100-year, 1-hour rainfall depth found in the NOAA Atlas 14
database. The calculation that has been used to determine the full detention volume required to
be detained on the property is shown in the spreadsheet below.
As required by the City of Aspen, a drywell must be sized for the capacity determined from the
full detention volume calculation for a 100-year, 1-hour storm if no overflow path for the BMP is
available. Since the drywell is sized for full detention, the Water Quality Capture Volume for the
onsite basin has been fulfilled. This volume will be used to adequately size the onsite drywell.
5.0 Hydraulic Criteria
The following analyses were performed using the peak flows of the sub basins described in
Section 4.2 of this report.
5.1 Inlets
The peak flows for the 100-year event in each sub-basin were used to size the proposed inlets.
Equations 4.17 through 4.20 from the URMP were used in these calculations. The equations
incorporate a 50 percent clogging factor and assume a 40 percent opening in the grates. Water
Rainfall depth, P1 (in)1.23 Soil Class B Intensity (in/hr)Discharge (ft3/Sec)Q=CIA t
The values shown in this table are analysing a 100-Year 1-Hour Storm Event. For basins with a flow length of less than 500 feet, a Time of Concentration of 5 minutes is assumed.
Developed Conditions
Sub Basin Total Area Impervious Area Percent Impervious C Value Time of Concentration Intensity Flow Rate
(Name)At (ft2) Ai (ft2)Ai/At (%)C (From Table) To (min)I (in/hr)Qs (ft3/sec)
1.1 413.98 413.98 100.00%0.89 5 6.33 0.05
1.2 728.11 181.29 24.90%0.52 5 6.33 0.05
1.3 246.54 246.54 100.00%0.89 5 6.33 0.03
1.4 768.06 0.00 0.00%0.43 5 6.33 0.05
1.5 661.32 0.00 0.00%0.43 5 6.33 0.04
1.6 601.74 601.74 100.00%0.89 5 6.33 0.08
1.7 550.64 161.46 29.32%0.54 5 6.33 0.04
1.8 1298.85 1298.85 100.00%0.89 5 6.33 0.17
1.9 664.23 664.23 100.00%0.89 5 6.33 0.09
1.10 518.00 123.79 23.90%0.52 5 6.33 0.04
1.11 720.24 624.36 86.69%0.82 5 6.33 0.09
Basin Flow Rate Calculations I =88.8P1(10 +Td )1.052
Basin Point of Concentration Total Area Impervious Area Impervious Full Detention Depth Factor of Safety Full Detention Storage
(Name) (name)(ft2)(ft2)(%)(in)(FOS)(ft3)
1 Drywell A 7171.71 4316.24 60.18%1.23 1 442
Full Detention Storage
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depths used in these calculations are based on the grading around each inlet and safe ponding
levels above the inlets. Each inlet takes the smaller value of the weir intersection capacity and
the orifice opening capacity, whichever is the smallest. The proposed dimensions of each inlet
must be greater than the subbasin peak flow for the 100-year storm. The tables below summarize
the calculations for each inlet as well as for the trench drains.
5.2 Pipes
The pipes were sized using the calculated flows from the sub-basins that release into them
through inlets and downspouts. The Time of Concentration (TOC) is below 5 minutes for all sub-
basins, so a reduction was not taken for the intensity. Depth of flow was also calculated in the
spreadsheets below to verify requirements set within the URMP. The pipes are all SDR-35 PVC
with a manning’s coefficient of .01. Design Q design / Q full values were compared to the wetted area
over the diameter squared for each pipe to generate the correct depth of water over diameter
pipe. All these ratio values are derived from the Manning’s Equation for partially full pipes. The
equations in Section 4.8.4 were used as the basis for these calculations. As specified in the
URMP, each pipe was confirmed to be less than 80% full for the 100-year 1-hour storm event.
Design charts giving Qdesign / Q full were downloaded from FHWA and the equations in Section
4.8.4 were used as the basis for these calculations. Calculated pipe sizes and depth of flow for
onsite pipes are shown below.
Effective Inlet Area, Ae (ft2)Inlet Orifice Capacity, Qo (ft3/s)Weir Flow Capacity, Qw (ft3/s)
Orifice Coefficient, Co 0.65 Clogging Factor, Cg 0.5 Area Opening Capacity Ratio, m
Weir Coefficient, Cw 3 Water Depth Above Inlet, Ys (ft)0.25 Effective Weir Length, Pe (ft)
Inlet Associated Subbasin Inlet Diameter Effective Inlet Area Orifice Flow Capacity Weir Flow Capacity Subbasin Flow
(Name)(Name)De (in)Ae (ft2)Qo (ft3/s)Qw (ft3/s)Q (ft3/s)
A2-Inlet 1.2 8 0.10 0.27 0.79 0.05
A7-Inlet 1.4 8 0.10 0.27 0.79 0.05
A10-Inlet 1.5 8 0.10 0.27 0.79 0.04
A14-Inlet 1.7 8 0.10 0.27 0.79 0.04
A18-Inlet 1.10 8 0.10 0.27 0.79 0.04
Round Inlet Capacity Calculation
0.6
Ae =1 −Cg (π(De /122)2)m Qo =Co Ae 2gYs Qw =Cw Pe Ys1.5
Pe =1 −Cg P
Effective Inlet Area, Ae (ft2)Wier Flow Capacity, Qw (ft3/s)
Orrifice Coefficient, Co 0.65 0.5 Area Opening Capacity Ratio, m
Weir Coefficient, Cw 3 0.25 Effective Weir Length, Pe (ft)
Inlet Associated Subbasin Inlet Length Inlet Width Effective Inlet Area Orifice Flow Capacity Wier Flow Capacity Subbasin Flow
(Name)(Name)(in)(in)Ae (ft2)Qo (ft3/s)Qw (ft3/s)Q (ft3/s)
A21-Trench Drain 1.11 228 6 2.85 7.43 7.31 0.09
Rectangular Inlet Capacity Calculation
0.6Clogging Factor, Cg
Water Depth Above Inlet, Ys (ft)
Inlet Orifice Capacity, Qo (ft3/s)𝐴𝑒=1 −𝐶𝑔(𝜋(𝐷𝑒/122)2)𝑚𝑄𝑜=𝐶𝑜𝐴𝑒2𝑔𝑌𝑠𝑄𝑤=𝐶𝑤𝑃𝑒𝑌𝑠1.5
𝑃𝑒=1 −𝐶𝑔𝑃
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6.0 Proposed Facilities
6.1 Drywells
The proposed dual chamber drywell meets the requirements of the URMP. The sizing of the
drywell is determined using the capacity calculations summarized in Section 4.4 of this drainage
report. Below is a summary showing the drywell dimensions to verify it has capacity. The chamber
divider, conical section, and sloped manhole lid were not included in these dimensions, which is
why the proposed drywells exceed the storage depth shown in the calculations.
7.0 Operation and Maintenance
7.1 Drywell
The drywell shall be inspected and maintained at least every three months to remove any
sediment, contaminants, and debris that has settled in the drywell. At minimum, the inspection
and maintenance of the drywell shall include the following steps:
Mannings Equation
(ft3/s)0.01
Note: Pipe Flow Rate (Qp) is the summation of the flow rates from the the collected sub basins through each pipe, or Qs.
Pipe Collected Sub Basins Pipe Flow Rate Slope Min. Pipe Diameter Prop. Pipe Diameter Pipe Max Flow Rate Percent of Capacity d/D Flow Depth Pipe Depth Percent
(Name)(#)Qp (ft3/sec)S (%) Dm(in) Dp(in)Qc (ft3/s) Qp/Qc (%)(Chart)d (%)
A1 1.1 0.05 1.00% 2.3 4 0.248 22%0.26 1.04 26%
A2 1.2 0.05 1.00% 2.3 4 0.248 22%0.27 1.08 27%
A3 1.1-1.2 0.11 1.00% 2.9 4 0.248 44%0.45 1.80 45%
A4 1.1-1.2 0.11 1.00% 2.9 4 0.248 44%0.45 1.80 45%
A5 1.1-1.2 0.11 1.00% 2.9 4 0.248 44%0.45 1.80 45%
A6 1.3 0.03 1.00% 1.9 4 0.248 13%0.18 0.72 18%
A7 1.1-1.4 0.19 1.00% 3.6 4 0.248 76%0.70 2.80 70%
A8 1.1-1.4 0.19 1.00% 3.6 4 0.248 76%0.70 2.80 70%
A9 1.1-1.4 0.19 1.00% 3.6 4 0.248 76%0.70 2.80 70%
A10 1.1-1.5 0.23 1.00% 3.9 6 0.731 31%0.35 2.10 35%
A11 1.6 0.08 1.00% 2.6 4 0.248 31%0.35 1.40 35%
A12 1.1-1.6 0.31 1.00% 4.3 6 0.731 42%0.43 2.58 43%
A14 1.7 0.04 1.00% 2.1 4 0.248 17%0.23 0.92 23%
A15 1.7-1.8 0.21 1.00% 3.8 4 0.248 85%0.79 3.16 79%
A16 1.7-1.8 0.21 1.00% 3.8 4 0.248 85%0.79 3.16 79%
A17 1.9 0.09 1.00% 2.7 4 0.248 35%0.37 1.48 37%
A18 1.9-1.10 0.12 1.00% 3.1 4 0.248 50%0.50 2.00 50%
A19 1.7-1.10 0.34 1.00% 4.5 6 0.731 46%0.46 2.76 46%
A20 1.7-1.10 0.34 1.00% 4.5 6 0.731 46%0.46 2.76 46%
A21 1.11 0.09 1.00% 2.7 4 0.248 35%0.37 1.48 37%
A22 1.7-1.11 0.42 1.00% 4.9 6 0.731 58%0.56 3.36 56%
Pipe Sectional Area (ft2)Manning Coefficient,
n
Min. Pipe Diameter,
Eq. 4-31 (ft)
City of Aspen Pipe Capacity Calculations
Ap =π Dp2 2 Qc = 1.49n Ap Dp48 2 3�SDm=nQpks 3/8
Drywell Name Associated Basin Drywell Diameter Storage Height Gravel Height Internal Capacity External Capacity Combined Capacity Calculated Volume Necessary
(Name)(Name)d (ft)h (ft)hg (ft)Vi (ft3)Ve (ft3) V (ft3)(ft3)
A 1 6 13 8 367.57 127.23 494.80 442.41
Storage Calculation - Drywells
Internal Capacity, Vi (ft3)External Capacity,Ve (ft3)Combined Capacity, V (ft3)Vi =hπ(d2)2 Ve =hg(π(d +1.52)2 −π(d2)2)V =Vi +Ve
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• Drywell shall be continuously inspected. At minimum, every three months and after every
storm event greater than ½ inches.
• Remove and dispose of any sediment, solids, debris, and any other waste. All material
removed from drywell shall be disposed of at a fitting disposal site and shall meet/comply
with all local, State, and Federal waste regulations/jurisdictions.
• Regularly inspect the drywells functionality in respect to the time it takes for water to drain
in the drywell to mee the maximum required infiltration time of 24 hours is not exceeded.
When drain down times in the drywell are larger than 24 hours, the drywell shall be drained
via pumping and the infiltrative area of the drywell shall be cleaned and all perforation in
the drywell shall be thoroughly washed out. If irregular drainage of the drywell continues
as described above, the system may be required to be replaced.
7.2 Inlets and Trench Drains
Trench drains and other linear drains shall be inspected and maintained on a regular basis to
prevent any clogging and debris from entering the storm system to provide correct functionality.
Grates and the adjacent areas to the trench drain shall be kept clean and clear of any leaves, soil,
and any other solid waste materials to prevent clogging or larger materials from entering in the
storm system. Drain sumps and catch basins shall be inspected, at the very minimum, every three
months and for each storm event that is greater than ½ inches in depth. All sediment shall be
cleaned out or vacuumed from the drain and catch basin. All sediment shall be disposed of
correctly, meeting local jurisdictional codes and requirements. Any damage to the grate and the
surrounding concrete shall be repaired correctly to maintain functionality of the drain. The grate
shall be replaced if excessive damage is present.
7.3 Pervious Pavers
Pervious pavers shall be inspected periodically to ensure long-term performance and infiltration
are working properly during its operational life. The most frequent issue with pervious pavers is
clogging caused by organic matter and other sediments. Inspection of the pervious pavers shall
be completed every three months and for any storm event that is greater than ½ inches of
rainfall depth. If clear backup of the pervious pavers is occurring, regenerative air vacuum
sweeping of the surface shall be completed. All removed aggregate during vacuuming shall be
replaced with the same materials as initially installed. It is also recommended that salt shall be
minimally used for ice melting and to prevent all soils from being washed into the pervious paver
surface. Routine sweeping of the pavement surface is recommended to removed potential
debris form entering the pervious paver section below the exposed surface. If consistent
clogging of the pavers is occurring, the entire paver section shall be replaced as defined in the
permitted civil plans to ensure functionality of the permeable properties of the pavement.
12/16/2022