HomeMy WebLinkAboutFile Documents.617 W Bleeker St.0062-2019-BRES (19)
Drainage Report
617 WEST BLEEKER ST.
ASPEN, CO
81611
September 26, 2019
Revised March 25, 2020
Prepared by
Richard Goulding, P.E.
Roaring Fork Engineering
592 Highway 133
Carbondale, CO 81623
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
Drainage Report
617 WEST BLEEKER ST.
ASPEN, CO
81611
I HEREBY AFFIRM THAT THIS REPORT FOR THE IMPROVEMENTS AT 617 WEST BLEEKER
STREET PREPARED BY ME FOR THE OWNERS THEREOF IN ACCORDANCE WITH THE
PROVISIONS OF CITY OF ASPEN AND APPROVED VARIANCES AND EXCEPTIONS LISTED
THERETO. I UNDERSTAND THAT IT IS THE POLICY OF THE CITY OF ASPEN THAT ASPEN DOES
NOT AND WILL NOT ASSUME LIABILITY FOR DRAINAGE FACILITIES DESIGNED BY OTHERS.
RICHARD GOULDING, P.E.
RFE Project # 2018-65
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
Table of Contents
1.0 General ................................................................................................................................. 4
1.1 Existing Site ..................................................................................................................... 4
1.2 Proposed Site .................................................................................................................... 5
1.3 Previous Drainage Studies ............................................................................................... 5
1.4 Offsite Drainage ............................................................................................................... 5
2.0 Drainage Basins and Sub-basins .......................................................................................... 5
2.1 Drainage Basins................................................................................................................ 6
2.2 Peak Discharge Calculations ............................................................................................ 6
3.0 Low Impact Site Design....................................................................................................... 8
3.1 Principles .......................................................................................................................... 8
4.0 Hydrological Criteria ........................................................................................................... 9
4.1 Storm Recurrence and Rainfall ........................................................................................ 9
4.2 Storage Volumes Methodology ........................................................................................ 9
5.0 Hydraulic Criteria .............................................................................................................. 10
5.1 Inlets ............................................................................................................................... 10
5.2 Pipes ............................................................................................................................... 10
6.0 Proposed Facilities ............................................................................................................. 13
6.1 Drywell ........................................................................................................................... 13
6.2 Pervious Pavers .............................................................................................................. 13
7.0 Operation and Maintenance ............................................................................................... 13
7.1 Drywell ........................................................................................................................... 13
7.2 7.2 Pervious Paver Area ................................................................................................. 14
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
4
1.0 General
1.1 Existing Site
617 West Bleeker Street, parcel number 273512444002, is located in Aspen, Colorado at the
west end, two blocks north of West Main Street within the City of Aspen limits. The site
contains an existing house with an approximate footprint of 2,574 square feet, a paved driveway
that extends into the Right-Of-Way on West Bleeker Street, and vegetation including large fir
trees, shrubs, and landscape lawn.
The parcel is surrounded by heavy vegetation. The topography is generally flat, but slopes away
from the two-story residence, through the highly vegetated area surrounding the property,
towards West Bleeker Street. An aerial photograph is provided as Figure 1. An existing
conditions sheet provided by the surveyor is part of the building permit set.
A geotechnical investigation was performed by Kumar & Associates on September 27, 2019. A
copy of the interim geotechnical report is included in the submittal package. The geotechnical
investigation resulted in one boring drilled in the northwest corner of the site. The first three feet
in the boring indicated silty sand and gravel fill overlaying dense, silty sand and gravel with
some cobbles. Auger refusal occurred 20 feet down. No free water was encountered in the
borings at the time of drilling and the subsoils were slightly moist to moist with depth. A
percolation rate of 2 inches per hour was documented in the interim report and was used for the
infiltration calculations in this report.
Figure 1: Aerial map of existing site.
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
5
1.2 Proposed Site
This project is classified as a βMajor Projectβ per Table 1.1. of the City of Aspen Urban Runoff
Management Plan (URMP). The proposed development is over 1,000 square feet and disturbs an
area of approximately 8,800 square feet, roughly 95 percent of the site. The intent of this report
is to demonstrate compliance with the requirements of the URMP. The Low Impact Design
(LID) Principles in the introduction of the manual were used as a guide throughout the design
process.
The proposed scope of work includes the demolition of an existing home and build of a two-
story, single family residence with a basement level, driveway, flagstone walkways, and a
concrete deck. There are a number of plantings and landscaped areas associated with this project
as well.
The topography of the parcel is relatively flat with existing grade typically draining away from
the site towards West Bleeker Street. The proposed drainage infrastructure includes area inlets
and a trench drain to convey flows to an onsite drywell for infiltration into the surrounding earth.
This drainage report will focus on the drainage basins being captured and conveyed by the storm
drainage system. The onsite basin that is no longer following historical runoff flow paths has
been analyzed for full detention design of a 100-year storm event.
1.3 Previous Drainage Studies
The analyzed parcel of land at 617 West Bleeker is located in basin, System 3, of the Aspen
Master Drainage plan. The City of Aspen public storm infrastructure is located three blocks
away from the property. Sheetflowing into the street is not possible due to grades and installing
infrastructure along 5th Street is not economically feasible for the project. Therefore, full
detention is proposed and will not impact the City of Aspenβs surface flows.
1.4 Offsite Drainage
The adjacent roads historically do not drain toward the property as there is an existing curb and
gutter adjacent to the property along the Right-of-Way. The site has a small swale on the west
and east side of the residence that will be kept post-development to not impact existing drainage
paths from neighboring properties. Offsite drainage will not be incorporated into the proposed
onsite storm system.
2.0 Drainage Basins and Sub-basins
The development on the parcel is proposed as one large onsite basin. This basin was then
subdivided into smaller sub-basins and analyzed to aid with design of the storm water
infrastructure. Basin and Sub-basin delineations are shown on sheets C4 and C5 of the submitted
civil drawings. These sheets list impervious areas, runoff coefficients, peak flows, and the
required volume of runoff to be detained.
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
6
2.1 Drainage Basins
Basin 1 is a major basin within the parcel and consists of the developed area of the residence,
including the snowmelted driveway, concrete deck, impervious roof, flagstone walkway, and
landscape areas sloped toward the home. The basin has a total area of 7,802 square feet and is
62% impervious. Impervious sections of the basin include the roof structure, snowmelted
driveway, flagstone walkway, and the concrete deck. The remainder of the basin is made up of
pervious landscaped areas and pervious paved patio sections that surrounds the residence. Runoff
from the basin is collected by area inlets, a trench drain, and downspouts. The runoff is conveyed
into a drywell which is sized for full detention of a 100-year storm event.
Sub-basins 1.1, 1.3, 1.6 and 1.8 include the impervious roof structure and is collected through a
system of gutter and downspouts. The concrete deck is included in the subbasin as well, with
drainage being routed through roof drains. All of the sub-basins within this overhead roof
structure are 100% impervious.
Sub-basin 1.2 includes the portion of flagstone walkway in the front yard along with landscaped
areas. All contributing flows are collected through an area drain. This sub-basin is 28%
impervious.
Sub-basins 1.4, 1.5 and 1.9 include pervious areas of the site that drain towards the residence.
Drainage within these sub-basins are almost entirely pervious, with small section of the driveway
adding minor impervious areas. These sub-basins are collected through area drains, set at low
points around the property, that tie into the onsite storm system.
Sub-basin 1.7 includes the impervious flagstone walkway along the eastern side of the
residence, along with some green space that drains toward the residence. Runoff is collected
through an area drain located in the landscaped area to the east of the proposed structure. This
subbasin is 28% impervious.
Sub-basin 1.10 is the impervious snowmelted driveway that slopes toward the garage. This
basin is 100.00% impervious and is collected through a trench drain within the driveway.
2.2 Peak Discharge Calculations
The peak flows were calculated for the Major Basin for 5 and 100-year storm events using the
Rational Method. The Rational Method is an acceptable method to calculate runoff for this basin
as the area is under 90 acres. Rainfall intensity was calculated using a Time of Concentration
(Td) of 5 minutes. The actual time of concentration for this site is less than 5 minutes, but
according to the City of Aspen URMP, equations used to calculate rainfall intensity are only
valid for a time of concentration of 5 minutes or greater so the smallest valid time of
concentration value was used. The 1-hour Rainfall depths (P1) used for these calculations was
taken from Table 2.2 of the URMP and is equal to 0.64 inches for the 5-year event and 1.23
inches for the 100-year event. Equation 2.1 was referenced when solving for the Rainfall
Intensity (I). π°π°= ππππ.ππ π·π·ππ(ππππ+π»π»π π )ππ.ππππππ (πΈπΈπΈπΈπΈπΈπΈπΈπΈπΈπΈπΈπΈπΈπΈπΈ 2.1)
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
7
Runoff Coefficients (C), a function of the Soil Group (in this case B for the onsite basin) and the
percentage of impervious area within each sub basin were developed using Figure 3.3. The
Runoff Coefficient (C) was then multiplied by the Rainfall Intensity (I) and the area of the Major
Basin (A, in acres) to determine the peak discharge. πΈπΈππ=πͺπͺπ°π°πͺπͺ ππππ=πππππΈπΈππ π·π·πΈπΈπ·π·π·π·βπΈπΈππππππ (π·π·πππ·π·) πΆπΆ=π π πΈπΈπΈπΈπΈπΈππππ πΆπΆπΈπΈπππππππΈπΈπ·π·πΈπΈπππΈπΈπΈπΈ πΌπΌ=π π πΈπΈπΈπΈπΈπΈπππΈπΈππππ πΌπΌπΈπΈπΈπΈπππΈπΈπ·π·πΈπΈπΈπΈπΌπΌ (πΈπΈπΈπΈπ·π·βπππ·π· ππππππ βπΈπΈπΈπΈππ) π΄π΄=π΄π΄πππππΈπΈ (πΈπΈπ·π·πππππ·π·)
These peak flow values were used to calculate the size of the proposed detention and conveyance
structures, such as the inlets, pipes and drywell. The tables below contain the peak flows for
developed and undeveloped conditions for 5 and 100-year storm events for the major basin, and
the 100-year peak flow rate for the sub basins.
5 Year Peak Discharge Developed Calculations
1 Hour(P 1)0.64
Return Period 5
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1)(ft2)(ft2)(%)From Table (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)
1 7082.01 4372.95 61.75%0.410 5 3.29 0.22
5 Year Peak Discharge Pre Development Calculations
1 Hour(P 1)0.64
Return Period 5
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1)(ft2)(ft2)(%)From Table (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)
1 7082.01 0.00 0.00%0.080 5 3.29 0.04
100 Year Peak Discharge Developed Calculations
1 Hour(P 1)1.23
Return Period 100
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1)(ft2)(ft2)(%)From Table (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)
1 7082.01 4372.95 61.75%0.570 5 6.33 0.59
100 Year Peak Discharge Pre Development Calculations
1 Hour(P 1)1.23
Return Period 100
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1)(ft2)(ft2)(%)From Table (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)
1 7082.01 0.00 0.00%0.350 5 6.33 0.36
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
8
3.0 Low Impact Site Design
Low Impact Development (LID) aims to mimic the natural pre-development hydrologic pattern.
The goal is to manage storm water as close to its source as is possible. This entire developed site
is approximately 62% percent impervious. The treatment train approach is used on all runoff to
increase water quality and infiltration.
3.1 Principles
Principle 1: Consider storm water quality needs early in the design process.
The grading and drainage design were coordinated between the architect, and civil engineering
teams throughout the design process and water quality requirements were discussed early on.
Site visits ensured proper understanding of existing conflicts and opportunities to improve
existing drainage patterns.
Principle 2: Use the entire site when planning for storm water quality treatment.
Storm water quality was considered in the design of every part of the site that is being affected
by the proposed construction. Sheet flowing runoff through landscaping is implemented, where
possible, to increase infiltration and water quality.
Principle 3: Avoid unnecessary impervious area.
The total impervious area on the site is kept to a minimum while meeting the architectural design
goals by incorporating pervious landscaped areas throughout the site. Pervious pavers are
utilized to reduce the amount of impervious area on site.
Principle 4: Reduce runoff rates and volumes to more closely match natural conditions.
All runoff from impervious surfaces on the property is collected and routed to BMP structures.
The infrastructure is sized to capture and infiltrate the 100-year runoff volume.
Principle 5: Integrate storm water quality management and flood control.
Water quality and flood control is accounted for in the design with six inch sumps proposed for
inlets to capture and detain runoff for a 100-year storm event.
Principle 6: Develop storm water quality facilities that enhance the site, the community and the
environment.
Full detention is proposed for all stormwater, meaning no runoff will be leaving the site. Swales
are proposed to keep runoff generated from the developed property, onsite.
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
9
Principle 7: Use treatment train approach.
The design implements sheetflow across landscaping, overland flow through grass-lined swales,
sumps in the pipe networks, and a multi chambered drywell to ensure treatment throughout the
system.
Principle 8: Design sustainable facilities that can be safely maintained.
Inlets and piping will be vacuumed or flushed periodically to maintain adequate flow. Proper
grading reduces dangerous slopes. Cleanouts are located where necessary to ensure the lifetime
of the drainage infrastructure. The drywell will be easily accessible for maintenance.
Principle 9: Design and maintain facilities with public safety in mind.
Proper drainage and grading of the driveway and walkways reduce ice buildup and dangerous icy
conditions. All grading was done with safety in mind and no steep slopes occur on the site.
4.0 Hydrological Criteria
4.1 Storm Recurrence and Rainfall
The property is located outside of the commercial core and isnβt served by any municipal storm
system, so this property classifies as a βSub-urban area not served by public storm sewerβ.
Therefore, the storm system for the site was designed to meet detention requirements for the 5
and 100-year historical storm events.
The 1-hour Rainfall depth (P1) is given in Table 2.2 as 0.64 inches for the 5-year event and 1.23
inches for the 100-year event. The Intensity in inches per hour for different storm duration (Td)
was calculated using Equation 2.1 from the City of Aspen URMP.
4.2 Storage Volumes Methodology
The storage requirements for this site were calculated using the total impervious area along with
the historic and developed peak runoff rates that were established in section 2.2. The proposed
storm drainage system is designed for full detention of a 100-year storm event. No detention is
required for pervious areas. Below is a summary of the required storage.
Full Detention Storage
Basin Total Area Impervious Area Impervious Full Detention Depth Required Storage BMP
(ft2)(ft2)(%)(in)(ft3)
1 7082.01 4372.95 61.75%1.23 448 DRYWELL A
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
10
5.0 Hydraulic Criteria
This property is not connected to the COAβs storm water infrastructure. All hydraulic
calculations are used to size onsite infrastructure. Below is a table that was used for an in-depth
analysis of the flows through the conveyance structures.
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
depths used in these calculations are based on the grading around each inlet and safe ponding
levels above the inlets. The tables on the following page summarize the calculations for each
inlet as well as for the trench drain.
5.2 Pipes
The pipes were sized by using the calculated flow from the sub-basins they are connected to.
Below is a table which groups what sub-basins are conveyed to each pipe. 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. The pipes are all SDR 35
PVC with a manningβs coefficient of 0.01.
100 Year Sub Basin Peak Discharge Developed Calculations
1 Hour(P 1)1.23
Return Period 100
Sub Basin Total Area Imp. Area Impervious C Value Time of C Intensity Sub Basin Flow Rate
(Name)At (ft2)Ai (ft2)Ai/At (%)From Table (Td)I=88.8P1/(10+Td)01.052 Qsub (ft3/sec)
1.1 301.18 301.18 100.00%0.950 5 6.33 0.04
1.2 475.67 135.28 28.44%0.460 5 6.33 0.03
1.3 312.78 312.78 100.00%0.950 5 6.33 0.04
1.4 575.83 0.00 0.00%0.350 5 6.33 0.03
1.5 692.10 20.00 2.89%0.350 5 6.33 0.04
1.6 1248.33 1248.33 100.00%0.950 5 6.33 0.17
1.7 537.03 151.00 28.12%0.460 5 6.33 0.04
1.8 1486.27 1486.27 100.00%0.950 5 6.33 0.21
1.9 756.38 21.67 2.86%0.350 5 6.33 0.04
1.10 696.44 696.44 100.00%0.950 5 6.33 0.10
Sub Basin and Circular Inlet Calculations
1 Hour(P 1)1.23 m=40%Ys=.04 (Depress inlet by 0.04')
Return Period 100 Cg=50%Co=0.65
Inlet ID Basin ID Total Area Imp. Area Impervious C Value
Concentration Intensity Q Max Inlet Type Diameter
Area(EQ. 4-20)Inlet Capacity (EQ 4-19)Has Capacity
See(D1)(ft2)(ft2)(%)From Table (Td)I=88.8P1/(10+Td)1.052 ft3/sec Wo (inches)Ae=(1-Cg)mA Q=CoAeβ2gYs (Yes/No)
A2-INLET 1.2 475.67 135.28 28.44%0.46 5 6.33 0.032 8" Round 8 0.070 0.081 Yes
A7-INLET 1.4 575.83 0.00 0.00%0.35 5 6.33 0.029 8" Round 8 0.070 0.081 Yes
A10-INLET 1.5 692.10 20.00 2.89%0.35 5 6.33 0.035 8" Round 8 0.070 0.081 Yes
A14-INLET 1.7 537.03 151.00 28.12%0.46 5 6.33 0.036 8" Round 8 0.070 0.081 Yes
A16-INLET 1.9 756.38 21.67 2.86%0.35 5 6.33 0.038 8" Round 8 0.070 0.081 Yes
Sub Basin and Rectangular Inlet Calculations
1 Hour(P1)1.23 m=40%Ys=.04 (Depress inlet by 0.04')
Return Period 100 Cg=50%Co=0.65
Inlet ID Basin ID Total Area Imp. Area Impervious C Value Time of Concentration Intensity Q Max Inlet Type Inlet Width Inlet Length Effective Open Area (EQ. 4-20)Inlet Capacity (EQ 4-19)Has Capacity
See(D1)(ft2)(ft2)(%)(From Table) (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)Rectangular Wo (inches)Lo (inches)Ae=(1-Cg)mWoLo Q=CoAeβ2gYs (Yes/No)
A18-TRENCH DRAIN 1.10 696.44 696.44 100.00%0.95 5 6.33 0.096 4" x 19.4'4 232.2 1.290 1.294 Yes
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
11
Design Q design / Q full charts were downloaded from FHWA. The equations in Section 4.8.4 was
used as the basis for these calculations.
Pipe sizes were tested for hydraulic capacity at 80 percent of their full flowrate. 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.
Storm System Pipes
Pipe System Pipe Contibuting Sub-Basins Design Flow Rate
Qdes
A1 1.1 0.04
A2 1.2 0.03
A3 1.1, 1.2 0.07
A4 1.1, 1.2 0.07
A5 1.3 0.04
A6 1.1-1.4 0.15
A7 1.1-1.4 0.15
A8 1.1-1.4 0.15
A9 1.1-1.4 0.15
A10 1.1-1.5 0.18
A11 1.6 0.17
A12 1.6 0.17
A13 1.1-1.6 0.35
A14 1.7 0.04
A15 1.7, 1.8 0.24
A16 1.9 0.04
A17 1.7-1.9 0.28
A18 1.10 0.10
A19 1.7-1.10 0.38
A20 1.7-1.10 0.38
A
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
12
K=0.462
Pipe Design Flow
Rate
Proposed
Slope
Manning
Coefficient
Required Pipe Diameter
Equation 4-31
Required Pipe
Diameter
Proposed Pipe
Diameter
Qdes (ft3/sec) S (%)n d (ft) = {nQdes/KβS}3/8 D req (in) D pro (in)
A1 0.04 1.00%0.01 0.17 2.05 4.0
A2 0.03 1.00%0.01 0.15 1.85 4.0
A3 0.07 1.00%0.01 0.21 2.54 4.0
A4 0.07 1.00%0.01 0.21 2.54 4.0
A5 0.04 1.00%0.01 0.17 2.08 4.0
A6 0.15 1.00%0.01 0.27 3.28 4.0
A7 0.15 1.00%0.01 0.27 3.28 4.0
A8 0.15 1.00%0.01 0.27 3.28 4.0
A9 0.15 1.00%0.01 0.27 3.28 4.0
A10 0.18 1.00%0.01 0.30 3.56 4.0
A11 0.17 2.00%0.01 0.26 3.07 4.0
A12 0.17 2.00%0.01 0.26 3.07 4.0
A13 0.35 1.00%0.01 0.38 4.58 6.0
A14 0.04 2.00%0.01 0.14 1.70 4.0
A15 0.24 2.00%0.01 0.29 3.48 4.0
A16 0.04 2.00%0.01 0.15 1.75 4.0
A17 0.28 2.00%0.01 0.31 3.68 4.0
A18 0.10 2.00%0.01 0.21 2.47 4.0
A19 0.38 2.00%0.01 0.34 4.11 6.0
A20 0.38 2.00%0.01 0.34 4.11 6.0
Pipe Sizing
Pipe Design Flow
Rate
Proposed Pipe
Diameter Slope 80% of Proposed
Pipe Diameter
Manning
Coefficient
Full Pipe Cross
Sectional Area Full Pipe Flow Rate Q Design /
Q Full d/D Hydraulic Grade Line
(Depth of Flow)
Depth of Flow Less Than
80% of Pipe Diameter
Qdes (ft3/sec) Dpro(in)S (%)Dpro*.8 (in)n A (ft) = Ο (Dpro/2)2 Qfull (ft3/s) = A(1.49/n)((Dpro/48)2/3)S1/2 Qdes/Qfull (from Chart)d (in) = (d/D)*Dpro (Yes/No)
A1 0.04 4.0 1.00%3.2 0.01 0.087 0.248 0.17 0.31 1.25 Yes
A2 0.03 4.0 1.00%3.2 0.01 0.087 0.248 0.13 0.28 1.10 Yes
A3 0.07 4.0 1.00%3.2 0.01 0.087 0.248 0.30 0.41 1.62 Yes
A4 0.07 4.0 1.00%3.2 0.01 0.087 0.248 0.30 0.41 1.62 Yes
A5 0.04 4.0 1.00%3.2 0.01 0.087 0.248 0.17 0.31 1.25 Yes
A6 0.15 4.0 1.00%3.2 0.01 0.087 0.248 0.59 0.62 2.46 Yes
A7 0.15 4.0 1.00%3.2 0.01 0.087 0.248 0.59 0.62 2.46 Yes
A8 0.15 4.0 1.00%3.2 0.01 0.087 0.248 0.59 0.62 2.46 Yes
A9 0.15 4.0 1.00%3.2 0.01 0.087 0.248 0.59 0.62 2.46 Yes
A10 0.18 4.0 1.00%3.2 0.01 0.087 0.248 0.73 0.70 2.81 Yes
A11 0.17 4.0 2.00%3.2 0.01 0.087 0.351 0.49 0.55 2.20 Yes
A12 0.17 4.0 2.00%3.2 0.01 0.087 0.351 0.49 0.55 2.20 Yes
A13 0.35 6.0 1.00%4.8 0.01 0.196 0.731 0.48 0.55 3.30 Yes
A14 0.04 4.0 2.00%3.2 0.01 0.087 0.351 0.10 0.25 1.00 Yes
A15 0.24 4.0 2.00%3.2 0.01 0.087 0.351 0.69 0.68 2.70 Yes
A16 0.04 4.0 2.00%3.2 0.01 0.087 0.351 0.11 0.25 1.00 Yes
A17 0.28 4.0 2.00%3.2 0.01 0.087 0.351 0.80 0.74 2.95 Yes
A18 0.10 4.0 2.00%3.2 0.01 0.087 0.351 0.27 0.38 1.52 Yes
A19 0.38 6.0 2.00%4.8 0.01 0.196 1.034 0.36 0.47 2.82 Yes
A20 0.38 6.0 2.00%4.8 0.01 0.196 1.034 0.36 0.47 2.82 Yes
Hydraulic Grade Line and Pipe Capacity
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
13
6.0 Proposed Facilities
This property is not connected to the COAβs storm water infrastructure, and the onsite BMP is
sized for full detention, as clarified in section 2.2 of this report. Pervious pavers are utilized in
some patios of the site to reduce to amount of impervious area to collect and detain.
Below are the analyses for the detention structureβs capacity and infiltration.
6.1 Drywell
Below is a table that shows the proposed drywell meeting the capacity required for full detention
of Basin 1.
Infiltration of the drywell is calculated using the percolation rate given by the interim
geotechnical report. The infiltration area is through the side of the gravel surrounding the
drywell. Infiltration through the bottom was disregarded due to potential for clogging.
6.2 Pervious Pavers
Pervious pavers are proposed on two patio areas for the project. The use of pervious pavers
reduces the imperviousness of the site and the amount of runoff to be detained on site.
Approximately 160 square feet of pervious pavers are proposed at the south end of the structure.
Six inches of fractured rock is proposed below the pervious pavers which promotes infiltration
below grade. The gravel also provides a small amount of storage during storm events to mitigate
any ponding close to the proposed structure.
7.0 Operation and Maintenance
7.1 Drywell
Drywells must be inspected and maintained quarterly to remove sediment and debris that has
washed into them. A maintenance plan shall be submitted to the City in the Drainage Report
describing the maintenance schedule that will be undertaken by the owners of the new residence
or building. Minimum inspection and maintenance requirements include the following:
β’ Inspect drywells at least four times a year and after every storm exceeding 0.5 inches.
β’ Dispose of sediment, debris/trash, and any other waste material removed from a drywell at suitable disposal sites and in compliance with local, State, and Federal waste regulations.
Drywell Storage
Drywell Basins Diameter Storage Depth Perforated Depth Internal Volume External (18" of Screened Rock) Volume Total Capacity Required Capacity
(Name)(#)D (ft)H (ft)P (ft)Ο*H*(D/2)2) (ft3)0.3*Ο*P*((D/2)+1.5)2 - (D/2)2) (ft3)(ft3)(ft3)
DRYWELL A 1 6 13 8 368 85 452 448
Drywell Infiltration
Name Diameter Perforation Height Perforated Area Total Capacity Infiltration Rate Infiltration Time Volume Infiltrated in 24 Hours
(Name)D (ft)H (ft)A (ft2) = 3.14*D*H V (ft3)I (in/hr)T (hr) = V/(A*I/12)Vtotal (ft3) = V*T
DRYWELL A 6 8 150.80 452.39 30 1.2 542.87
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.
14
β’ Routinely evaluate the drain-down time of the drywell to ensure the maximum time of 24
hours is not being exceeded. If drain-down times are exceeding the maximum, drain the
drywell via pumping and clean out the percolation area (the percolation barrel may be jetted
to remove sediment accumulated in perforations. If slow drainage persists, the system may
need to be replaced.
7.2 7.2 Pervious Paver Area
As per section 8.5.3.1 of the URMP, the following schedule will be undertaken by the owners of
the property to achieve long term performance of the BMPβs.
04/13/2020
Reviewed by Engineering
06/26/2020 9:05:09 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.