HomeMy WebLinkAboutFile Documents.805 Roaring Fork Rd.0235.2018 (4).ARBK
Drainage Report
805 ROARING FORK ROAD
ASPEN, CO
81611
April 20th, 2018
Revised June 6th, 2018
Revised July 24th, 2018
Revised September 4th, 2018
Prepared by Richard Goulding, P.E.
Roaring Fork Engineering
592 Highway 133
Carbondale, CO 81623
02/11/2019
Reviewed by Engineering
03/04/2019 4:39:20 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.
Drainage Report
805 ROARING FORK ROAD
ASPEN, CO
81611
I HEREBY AFFIRM THAT THIS REPORT FOR THE IMPROVEMENTS AT 805 ROARING FORK
ROAD WAS PREPARED BY ME FOR THE OWNERS THEREOF IN ACCORDANCE WITH THE
PROVISIONS OF PITKIN COUNTY AND APPROVED VARIANCES AND EXCEPTIONS LISTED
THERETO. I UNDERSTAND THAT IT IS THE POLICY OF PITKIN COUNTY THAT PITKIN COUNTY
DOES NOT AND WILL NOT ASSUME LIABILITY FOR DRAINAGE FACILITIES DESIGNED BY
OTHERS.
RICHARD GOULDING, P.E.
RFE Project # 2017-61
02/11/2019
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 .......................................................................................... 7
2.1 Drainage Basins ................................................................................................................ 7
2.2 Peak Discharge Calculations ............................................................................................ 8
3.0 Low Impact Site Design....................................................................................................... 9
3.1 Principles .......................................................................................................................... 9
4.0 Hydrological Criteria ......................................................................................................... 11
4.1 Storm Recurrence and Rainfall ...................................................................................... 11
4.2 Storage Volumes Methodology ...................................................................................... 11
5.0 Hydraulic Criteria .............................................................................................................. 11
5.1 Inlets ............................................................................................................................... 12
5.2 Pipes ............................................................................................................................... 12
6.0 Proposed Facilities ............................................................................................................. 15
6.1 Pervious Paver Subbase ................................................................................................. 15
6.2 Drywell ........................................................................................................................... 15
7.0 Operation and Maintenance ............................................................................................... 16
7.1 Drywell ........................................................................................................................... 16
7.2 Pervious Paver Area ....................................................................................................... 16
7.3 Biodetention Basins ........................................................................................................ 17
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1.0 General
1.1 Existing Site
805 Roaring Fork Road is located in Aspen, Colorado at the south end of Roaring Fork Road,
north of Highway 82 within the City of Aspen limits. The site contains an existing house with an
approximate footprint of 4,100 square feet, three stone patios, a paved driveway that extends into
the Right-Of-Way on North 3rd Street, approximately 285 square feet of gravel parking adjacent
to Roaring Fork Road, and vegetation including large fir trees, aspens, 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, down
toward both Roaring Fork Road and N. 3rd Street. An aerial photograph is provided as Figure 1.
An existing conditions sheet is part of the building permit set.
A geotechnical report was developed by HP Kumar and is dated November 1, 2017. A copy of
the geotechnical report is included in the submittal package. The geotechnical investigation
resulted in an observation of relatively dense, silty sand and gravel with cobbles and possible
boulders found below the driveway on the west side of the property. No free water was
encountered in the borings at the time of drilling and the subsoils were slightly moist to moist
with depth. Graphic logs of the subsurface conditions encountered at the site are shown on
Figure 2 of the geotechnical report. A percolation rate of 6 inches per hour was documented in
the report and was used for the infiltration calculations in this report.
Figure 1: Aerial map of existing site.
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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 11,000 square feet, roughly 90 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 renovation of a two-story, single family residence with
a basement level, driveway, and hardscape areas including a pathway around the house, three
patios and a walkway from an off-street parking spot on Roaring Fork Road. 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 the existing roads on either side of the property. The proposed drainage
infrastructure includes an onsite drywell and an offsite screened rock bed. This drainage report
will focus on the onsite and offsite basins being captured and conveyed by the storm drainage
systems. The onsite basin that is no longer following historical runoff flow paths has been
analyzed for full detention of a 100-year storm event. The screened rock bed is designed for
water quality capture volume of a 100-year storm event for offsite basin 2.
1.3 Previous Drainage Studies
The parcel of land belonging to 805 Roaring Fork Road is located in basin 8, a 53.8-acre portion
of System 3 of the Aspen Master Drainage plan. The site is not located close enough to City of
Aspen drainage infrastructure to feasibly utilize. Full detention is being implemented, and
therefore will not affect the cityβs stormwater system capacity.
1.4 Offsite Drainage
The adjacent roads historically drain into the vegetation along the road within the right of way.
An offsite basin, OS1, along N. 3rd Street was analyzed to ensure that the existing swale in the
right-of-way has capacity for full detention of the impervious area for a 100-year storm event
and will not overflow onto the property. This existing swale will be maintained to ensure that
this basin functions as intended. Roaring Fork Road, labeled OS2 for calcs, historically does not
flow onto the property as there is a berm within the right of way about 5β from the edge of road,
however, as a measure of mitigation, the existing gravel parking is proposed to be renovated with
pervious pavers and a screen rock subbase to capture the 100-year water quality capture volume.
The basins have been labeled OS1 and OS2, respectively, and are presented on page C.03 of the
civil set.
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Offsite 5 Year Peak Discharge Developed Calculations
1 Hour(P1)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)
OS1 10721.77 5482.00 51.13%0.350 5 3.29 0.28
OS2 4201.70 4201.70 100.00%0.896 5 3.29 0.28
Offsite 5 Year Peak Discharge Pre Development Calculations
1 Hour(P1)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)
OS1 10721.77 0.00 0.00%0.080 5 3.29 0.06
OS2 4201.70 0.00 0.00%0.080 5 3.29 0.03
Offsite 100 Year Peak Discharge Developed Calculations
1 Hour(P1)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)
OS1 10721.77 5482.00 51.13%0.520 5 6.33 0.81
OS2 4201.70 4201.70 100.00%0.950 5 6.33 0.58
Offsite 100 Year Peak Discharge Pre Development Calculations
1 Hour(P1)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)
OS1 10721.77 0.00 0.00%0.350 5 6.33 0.54
OS2 4201.70 0.00 0.00%0.350 5 6.33 0.21
Offsite Full Detention Storage
Basin Total Area Impervious Area Impervious Full Detention Depth Factor of Safety Required Storage BMP
(ft2)(ft2)(%)(in)F.O.S.(ft3)
OS1 10721.77 5482.00 51.13%1.23 1 562 Offsite Biodetention Basin
Offsite Biodetention Basins
Storage System Basins Sectional Area Length Total Capacity Required Capacity
(Name)(#)(ft2)(ft)(ft3)(ft3)
Offsite Biodetention Basin OS1 4 175 700.00 562
Water Quality Capture Volume Storage
Basin Total Area Impervious Area Impervious WQCV Table Value WQCV Storage Required Storage BMP
(#)(ft2)(ft2)(%)(in)(ft3)(ft3)
OS2 4201.70 4201.70 100.00%0.255 89.29 89.3 Pervious Paver Subbase
Pervious Paver Subbase
Storage System Basins Area Depth Void Ratio Total Capacity Required Capacity
(Name)(#)(ft2)(ft)(ft3)(ft3)
Pervious Paver Subbase OS2 285 1.25 0.3 106.88 89
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The neighboring property detains their flows on-site and Aspen GIS topography mapping, Index:
2735_12, shows that the neighboring property will transport any un-detained water to the north
and away from 805 Roaring Fork Road.
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 sheet C.03 and C.04. These sheets
list impervious areas, runoff coefficients, peak flows, and the required volume of runoff to be
detained.
2.1 Drainage Basins
Basin 1 is a major basin within the parcel and consists of the developed area of the residence,
including the driveway, walkways, patio, the roof, and several lawn areas. The basin has a total
area of 12,129 square feet and is 52.21% impervious. Impervious sections of the basin include
the roof structure, driveway and patio surfaces. The remainder of the basin is made up of
pervious landscaped areas that surround the residence. Runoff from the basin is collected by
sheet flowing to inlets and downspouts. The runoff is conveyed into Drywell A and Drywell B,
which are sized for full detention of a 100-year storm event.
Sub-basin 1.1 consists of the landscaping to the south of the residence. The basin is graded to
slope to an inlet next to the pervious pavers, which will collect any excess runoff and convey it
through pipe system A to the drywells.
Sub-basin 1.2 includes the southwest portion of the impervious roof that will be collected by
downspout A3 and conveyed through pipe system A.
Sub-basin 1.3 is the driveway located on the west side of the residence. Runoff from the
snowmelted driveway will be collected so it does not disperse onto the right of way asphalt. The
sub basin is sloped to a trench drain, which collects the runoff and conveys it in pipe system A to
the drywells.
Sub-basin 1.4 includes the northwest portion of the impervious roof that will be collected by
downspout A7 and conveyed through pipe system A.
Sub-Basin 1.5 includes the A/C unit and utility pads and is collected to an area drain and
conveyed through pipe system A to the drywells.
Sub-Basin 1.6 includes the northeast portion of the impervious roof that will be collected by
downspout A9 and conveyed through pipe system A.
Sub-Basin 1.7 includes the back patio next to the spa, a walkway, and the landscaped areas
surrounding the patio. This basin is collected by an inlet where it is conveyed to the drywells.
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Sub-Basin 1.8 includes the east portion of the impervious roof that will be collected by
downspouts A12 and A13 and conveyed through pipe system A.
Sub-Basin 1.9 includes the snowmelted portion of the back patio next to the spa, a walkway, and
the planter area. This basin is collected by an inlet where it is conveyed to the drywells.
Sub-basin 1.10 is the portion of the roof that is included in the basin. B1 downspout captures the
roof and the runoff is conveyed through pipe system B to the drywells.
Sub-basin 1.11 includes landscaped areas, with patios and pervious walkways. The stormwater
runoff from impervious areas is collected at an area drain and conveyed through pipe system B to
the drywells.
Sub-basin 1.12 is an area including landscaping and a patio surface that drains to an inlet next to
the pervious pavers. This inlet connects into pipe system B.
Sub-basin 1.13 includes the eastern roof of the residence. B4 downspout is piped into system B.
Sub-Basin 1.14 includes the backyard of the residence to the north, this area is graded to
sheetflow to a concentrated point of Drywell A.
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)
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 πΈπΈπΈπΈπΈπΈπππΈπΈπ π π π πΌπΌπΈπΈπΈπΈπππΈπΈπ·π·πΈπΈπΈπΈπΌπΌ (πΈπΈπΈπΈπ·π·βπππ·π· ππππππ βπΈπΈπΈπΈππ) π΄π΄=π΄π΄πππππΈπΈ (πΈπΈπ·π·πππππ·π·)
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These peak flow values were used to calculate the size of the proposed detention and conveyance
structures, such as swales, drywells, inlets and pipes. 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.
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 52 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 was coordinated between the architect, landscape 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.
5 Year Peak Discharge Developed Calculations
1 Hour(P1)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 12129.27 6332.75 52.21%0.350 5 3.29 0.32
5 Year Peak Discharge Pre Development Calculations
1 Hour(P1)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 12129.27 0.00 0.00%0.080 5 3.29 0.07
100 Year Peak Discharge Developed Calculations
1 Hour(P1)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 12129.27 6332.75 52.21%0.520 5 6.33 0.92
100 Year Peak Discharge Pre Development Calculations
1 Hour(P1)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 12129.27 0.00 0.00%0.350 5 6.33 0.62
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Storm water quality was considered in the design of every part of the site that is being affected
by the proposed construction. sheetflowing runoff through landscaping was implemented to
increase infiltration and water quality.
Principle 3: Avoid unnecessary impervious area.
The total impervious area on the site was kept to a minimum while meeting the architectural
design goals by incorporating pervious landscaped areas throughout the site. All walkways were
designed with pervious pavers to reduce impervious area.
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 has been sized to capture and infiltrate all the 100-year runoff volume.
Principle 5: Integrate storm water quality management and flood control.
By keeping the existing biodetention basin in the right of way, implications on the right of way
will be minimal. Water quality was maintained within the flood control design through sheet
flowing runoff through landscaping, sumps, and pervious pavers.
Principle 6: Develop storm water quality facilities that enhance the site, the community and the
environment.
The design is proposing full detention for all stormwater, meaning no runoff will be leaving the
site. Depressions are continued to be used to ensure proper drainage of the right of way.
Principle 7: Use treatment train approach.
The design implements sheetflow across landscaping, pervious pavers, sumps in the pipe
networks, and multi chambered drywells 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 and proper drainage to reduce ice buildup. 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 reduces ice buildup and dangerous
icy conditions. All grading was done with safety in mind, and no steep slopes occur on the site.
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4.0 Hydrological Criteria
4.1 Storm Recurrence and Rainfall
The property is located outside of the commercial core and isnβt served by any 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.
5.0 Hydraulic Criteria
This property is not connected to the COAβs storm water infrastructure. All hydraulics are sized
for onsite infrastructure. Below is a table that was used for an in-depth analysis of the flows
through the conveyance structures.
Full Detention Storage
Basin Total Area Impervious Area Impervious Full Detention Depth Factor of Safety Required Storage BMP
(ft2)(ft2)(%)(in)F.O.S.(ft3)
1 12129.27 6332.75 52.21%1.23 1 649 Drywell A and B
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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 drains.
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
100 Year Sub Basin Peak Discharge Developed Calculations
1 Hour(P1)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 2658.75 200.70 7.55%0.380 5 6.33 0.15
1.2 990.63 990.63 100.00%0.950 5 6.33 0.14
1.3 632.30 632.30 100.00%0.950 5 6.33 0.09
1.4 1008.51 1008.51 100.00%0.950 5 6.33 0.14
1.5 59.82 59.82 100.00%0.950 5 6.33 0.01
1.6 812.10 812.10 100.00%0.950 5 6.33 0.11
1.7 689.59 323.56 46.92%0.510 5 6.33 0.05
1.8 553.58 553.58 100.00%0.950 5 6.33 0.08
1.9 129.00 48.63 37.70%0.490 5 6.33 0.01
1.10 985.80 985.80 100.00%0.950 5 6.33 0.14
1.11 1328.08 149.75 11.28%0.400 5 6.33 0.08
1.12 608.98 0.00 0.00%0.350 5 6.33 0.03
1.13 567.37 567.37 100.00%0.950 5 6.33 0.08
1.14 1104.76 0.00 0.00%0.350 5 6.33 0.06
Sub Basin and Circular 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
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)
A1-Inlet 1.1 2658.75 200.70 7.55%0.380 5 6.33 0.147 12" Round 12 0.157 0.183 Yes
A10-Inlet 1.5 59.82 59.82 100.00%0.950 5 6.33 0.008 6" Round 6 0.039 0.046 Yes
A11-Inlet 1.7 689.59 323.56 46.92%0.510 5 6.33 0.051 8" Round 8 0.070 0.081 Yes
A14-Inlet 1.9 129.00 48.63 37.70%0.490 5 6.33 0.009 8" Round 8 0.070 0.081 Yes
B2-Inlet 1.11 1328.08 149.75 11.28%0.400 5 6.33 0.077 8" Round 8 0.070 0.081 Yes
B3-Inlet 1.12 608.98 0.00 0.00%0.350 5 6.33 0.031 6" Round 6 0.039 0.046 Yes
C1-Inlet 1.14 1104.76 0.00 0.00%0.350 5 6.33 0.056 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)
A11-Trench Drain 1.3 632.30 632.30 100.00%0.950 5 6.33 0.087 4" x 18'4 216 1.200 1.204 Yes
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intensity. Depth of flow was also calculated in the spreadsheets below. The pipes are all SDR 35
PVC with a manningβs coefficient of .01.
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
A A1 1.1 0.15
A2 1.1 0.15
A3 1.2 0.14
A4 1.1-1.2 0.28
A5 1.3 0.09
A6 1.1-1.3 0.37
A7 1.1-1.4 0.51
A8 1.1-1.4 0.51
A9 1.6 0.11
A10 1.1-1.6 0.63
A11 1.1-1.7 0.68
A12 1.8 0.08
A13 1.8 0.08
A14 1.1-1.9 0.77
A15 1.1-1.13 1.09
B1 1.10 0.14
B2 1.10,1.11 0.21
B3 1.10-1.12 0.24
B4 1.13 0.08
B5 1.10-1.13 0.32
C C1 1.14 0.06
B
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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 Dreq (in) Dpro (in)
A1 0.15 1.50%0.01 0.25 3.05 4.0
A2 0.15 1.50%0.01 0.25 3.05 4.0
A3 0.14 1.50%0.01 0.25 2.97 4.0
A4 0.28 1.50%0.01 0.33 3.90 4.0
A5 0.09 1.50%0.01 0.21 2.51 4.0
A6 0.37 1.50%0.01 0.36 4.32 6.0
A7 0.51 1.50%0.01 0.41 4.87 6.0
A8 0.51 1.50%0.01 0.41 4.87 6.0
A9 0.11 1.50%0.01 0.23 2.76 4.0
A10 0.63 1.50%0.01 0.44 5.27 6.0
A11 0.68 1.50%0.01 0.45 5.42 6.0
A12 0.08 1.50%0.01 0.20 2.39 4.0
A13 0.08 1.50%0.01 0.20 2.39 4.0
A14 0.77 1.50%0.01 0.47 5.67 6.0
A15 1.09 1.50%0.01 0.54 6.47 8.0
B1 0.14 1.50%0.01 0.25 2.96 4.0
B2 0.21 1.50%0.01 0.29 3.51 4.0
B3 0.24 1.50%0.01 0.31 3.69 4.0
B4 0.08 1.50%0.01 0.20 2.41 4.0
B5 0.32 1.50%0.01 0.34 4.10 6.0
C1 0.06 1.50%0.01 0.18 2.13 4.0
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 0.15 4.0 1.50%3.2 0.01 0.087 0.304 0.48 0.55 2.20 Yes
A2 0.15 4.0 1.50%3.2 0.01 0.087 0.304 0.48 0.55 2.20 Yes
A3 0.14 4.0 1.50%3.2 0.01 0.087 0.304 0.45 0.52 2.06 Yes
A4 0.28 6.0 1.50%4.8 0.01 0.196 0.895 0.32 0.43 2.58 Yes
A5 0.09 4.0 1.50%3.2 0.01 0.087 0.304 0.29 0.41 1.62 Yes
A6 0.37 6.0 1.50%4.8 0.01 0.196 0.895 0.41 0.50 3.00 Yes
A7 0.51 6.0 1.50%4.8 0.01 0.196 0.895 0.57 0.60 3.60 Yes
A8 0.51 6.0 1.50%4.8 0.01 0.196 0.895 0.57 0.60 3.60 Yes
A9 0.11 4.0 1.50%3.2 0.01 0.087 0.304 0.37 0.47 1.88 Yes
A10 0.63 6.0 1.50%4.8 0.01 0.196 0.895 0.70 0.69 4.14 Yes
A11 0.68 6.0 1.50%4.8 0.01 0.196 0.895 0.76 0.73 4.35 Yes
A12 0.08 4.0 1.50%3.2 0.01 0.087 0.304 0.25 0.38 1.52 Yes
A13 0.08 4.0 1.50%3.2 0.01 0.087 0.304 0.25 0.38 1.52 Yes
A14 0.77 6.0 1.50%4.8 0.01 0.196 0.895 0.86 0.78 4.68 Yes
A15 1.09 8.0 1.50%6.4 0.01 0.349 1.928 0.56 0.60 4.80 Yes
B1 0.14 4.0 1.50%3.2 0.01 0.087 0.304 0.45 0.52 2.06 Yes
B2 0.21 4.0 1.50%3.2 0.01 0.087 0.304 0.70 0.69 2.76 Yes
B3 0.24 4.0 1.50%3.2 0.01 0.087 0.304 0.80 0.75 3.00 Yes
B4 0.08 4.0 1.50%3.2 0.01 0.087 0.304 0.26 0.38 1.52 Yes
B5 0.32 6.0 1.50%4.8 0.01 0.196 0.895 0.36 0.47 2.82 Yes
C1 0.06 4.0 1.50%3.2 0.01 0.087 0.304 0.18 0.33 1.30 Yes
Hydraulic Grade Line and Pipe Capacity
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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. The offsite Pervious Paver
system has been sized for water quality. Below are the analyses for the individual detention
structureβs capacity and infiltration.
6.1 Pervious Paver Subbase
Below are tables that show the proposed capacities meet the required volume of the screened
rock subbase used in the design. The area in the table is the surface area of the pavers that are
placed on top of the bed and the depth is the distance from the bottom of the screened rock to the
surface of the pervious pavers.
Infiltration of the subbase is shown below and uses the percolation rate given by the
Geotechnical report. The infiltration area is the side of the gravel bed. Infiltration through the
bottom was disregarded due to potential for clogging. The table below shows that the screened
rock bed infiltration rates meet the City of Aspenβs requirements.
6.2 Drywell
Below is a table that shows the proposed drywells meet the capacity required for full detention of
basin 1.
Infiltration of the drywell is calculated using the percolation rate given by the 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.
Pervious Paver Subbase
Storage System Basins Area Depth Void Ratio Total Capacity Required Capacity
(Name)(#)(ft2)(ft)(ft3)(ft3)
Pervious Paver Subbase OS2 285 1.25 0.3 106.88 89
Full Detention Infiltration
BMP Max Volume Infiltration Area Infiltration Rate Time To Drain Volume Infiltrated in 24 Hours
(name)V (ft3)A (ft2)I (in/hr)(hr)Vtotal (ft3) = V*24/T
Pervious Paver Subbase 106.88 285 6 0.75 3420.00
Drywell Storage
NOTE: DRYWELL A AND DRYWELL B SHARE THE CAPACITY FOR THE TOTAL DETENTION FOR BASIN 1
Drywell Basins Diameter Storage Depth Internal Volume External (18" of Screened Rock) Volume Total Capacity Required Capacity
(Name)(#)D (ft)H (ft)Ο*H*(D/2)2) (ft3)0.3*Ο*4*((D/2)+1.5)2 - (D/2)2) (ft3)(ft3)(ft3)
Drywell A 1 6 10 283 42 325 325
Drywell B 1 6 10 283 42 325 325
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 8 4 100.53 325.00 6 6.465669563 2101.34
Drywell B 8 4 100.53 325.00 6 6.465669563 2101.34
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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.
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 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.
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The perforated pipes should be cleaned and flushed yearly using the cleanouts on either end of
the pipe. Do not use soap or chemicals to clean the drain. Inspect annually during a storm event
to insure performance of drainage. If the drain has clogged outside of the drain pipe within the
gravel bed, further maintenance or replacement of the gravel bed may be required. To access the
gravel bed, the pavers can be lifted, where the sand, filter fabric, and gravel detention bed can be
repaired as necessary. The pavers can be maintained similar to the recommended pervious paver
table 8.8 above, following the schedule as per section 8.5.3.1 of the URMP.
7.3 Biodetention Basins
Biodetention basins are generally considered a low-maintenance stormwater management
approach. The depressions should be landscaped with grasses and plants to the maximum extent
possible. Do not fill the depression with mulch, gravel, or any fill material, as the capacity of the
basin will be minimized. Plant maintenance will occur as needed, including mowing, irrigation
(if necessary), and pruning. Remove any debris that collects in the depression during general
landscape maintenance.
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