HomeMy WebLinkAboutFile Documents.855 Chatfield Rd.0072-2020-BRES (24)
Drainage Report
855 CHATFIELD ROAD
ASPEN, CO 81611
June 26th 2020
Prepared by Richard Goulding, P.E.
Roaring Fork Engineering
592 Highway 133
Carbondale, CO 81623
07/09/2020
Drainage Report
855 CHATFIELD ROAD
ASPEN, CO 81611
I HEREBY AFFIRM THAT THIS REPORT FOR THE IMPROVEMENTS AT 855 CHATFIELD ROAD
WAS 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 # 2019-57
07/09/2020
Table of Contents
1.0 General ................................................................................................................................. 4
1.1 Existing Site ..................................................................................................................... 4
1.2 Proposed Site .................................................................................................................... 4
1.3 Previous Drainage Studies ............................................................................................... 5
1.4 Offsite Drainage ............................................................................................................... 5
2.0 Drainage Basins and Sub-basins .......................................................................................... 6
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 5.1 Inlets ......................................................................................................................... 11
5.2 5.2 Pipes ......................................................................................................................... 12
5.3 Valley pan ...................................................................................................................... 17
6.0 Proposed Facilities ............................................................................................................. 19
6.1 Drywell ........................................................................................................................... 19
7.0 Operation and Maintenance ............................................................................................... 19
7.1 Inlets and Piping ............................................................................................................. 19
7.2 Trench Drains and Slot Drains ....................................................................................... 19
7.3 Drywell ........................................................................................................................... 20
7.4 Pervious Paver Area ....................................................................................................... 20
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1.0 General
1.1 Existing Site
The following report is an evaluation of the proposed redevelopment of the existing residence at
855 Chatfield Road in Aspen, Colorado, parcel number 273502402006. The property is located on
the west side of the road and overlooks the Maroon Creek drainage. The site contains a single-
family residence with a garage, consisting of an approximate footprint of 3,400 square feet. The
site has extensive hardscape patios and walkways, large existing trees, landscaped areas, and a
looped driveway. There are neighboring properties with single-family residences located to the
south and north, with the right of way to the east and Aspen Golf Course on the other side of the
street, and an empty lot to the west. The existing topography is sloping to the west, and steeper
slopes are found in the northwest corner of the lot. Maroon Creek drainage drops in elevation
shortly after the property line to the west. The City of Aspen city limits borders the west side of
the property. An existing conditions sheet has been included in the submitted building permit
drawings. Utilities are all located in the right of way to the east of the site with utility services
connecting to the existing house.
Figure 1: Pitkin County GIS vicinity view. Parcel 273502402006 shown in red.
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 that exceeds 25% of the entire 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. Onsite storm infrastructure has
been sized to convey runoff for a 100-year storm event.
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The existing residence will be entirely demolished and replaced with the proposed residence with
a footprint of 3300 square feet. A walkout basement will exit on the west side of the residence,
with extensive landscaping, walls, walkways, spa, and a fire feature transitioning into the main
level. Landscaping, patios, and walkways are proposed around the rest of the site. A garage will
be located on the east end of the residence, with a driveway sloped to the west from the right of
way.
The proposed drainage infrastructure includes downspouts from roof structures, trench drains and
inlets within hardscaped areas, and area drains surrounding the site capture on-site flows before
they reach the adjacent properties. All onsite drainage is captured from impervious areas and is
routed through an onsite pipe system that connects to a drywell located in the garage.
Improvements will be made to the right of way, including a clean transition from the asphalt into
landscaping, utility upgrades, and a valley pan to manage storm runoff.
1.3 Previous Drainage Studies
The City of Aspen updated their URMP in 2001 and the property is within the boundaries of the
study. The study indicates that the property is not within a Mudflow area.
1.4 Offsite Drainage
A small offsite basin affects the site, including a portion of the right of way flowing onto the site.
An analysis was performed to determine sizing for a valley pan in order to convey runoff from
sheetflowing down the driveway. The flowrates for peak runoff were determined for the basin for
a 5- and 100-year storm event using the equations found in section 2.2 of this drainage report. See
tables below for calculated values.
Offsite 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 1059.00 1059.00 100.00%0.896 5 3.29 0.07
Offsite 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 1059.00 0.00 0.00%0.080 5 3.29 0.01
07/09/2020
No drywell is shown in the
garage on the plans.
6
2.0 Drainage Basins and Sub-basins
The development on the parcel is proposed as two large onsite basins and one small basin for
conveyance of pervious areas away from the structure. These basins will be subdivided into smaller
sub-basins and analyzed to aid with design of the storm water infrastructure. Basin delineation is
shown on sheet C4. This sheet lists impervious area, 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 concrete driveway, impervious walkways, and the roof. The basin has a total area of
6644 square feet and is 78% impervious. The remaining pervious areas of the basin include several
landscaped areas surrounding the residence. Runoff from the basin is collected through trench
drains, area drains, and downspouts from the roof. The captured runoff is then conveyed through
the piping system to a drywell in the driveway that is sized for full detention.
Basin 2 consists of the developed area of the residence and includes the backyard, which contains
roof downspouts, patios, walkways, and landscaped areas. The basin has a total area of 4714 square
feet and is 50% impervious. Runoff from the basin is collected through a trench drain, area drains,
and downspouts from the roof. The captured runoff is conveyed to a drywell in the landscaping
that is sized for full detention.
Basin 3 is a portion of landscaping to the north of the residence. It has a total area of 344 square
feet and is 0% impervious. Runoff from the basin is collected through perforated pipes that convey
excess water from landscaped areas. The captured runoff is conveyed to an area north of the basin
and released onto the hillside. riprap is located at the overflow to prevent erosion.
2.2 Peak Discharge Calculations
The peak flows were calculated for the onsite basins for the 5-year and 100-year storm event 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
Offsite 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 1059.00 1059.00 100.00%0.950 5 6.33 0.15
Offsite 100 Year Peak Discharge Pre Development Calculations
1 Hour(P 1)1.23
Return Period 10
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 1059.00 0.00 0.00%0.350 5 6.33 0.05
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(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 were taken from Table 2.2 of
the URMP and are 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 (πΈπΈπΈπΈ.2.1)
Runoff Coefficients (C), a function of the Soil Group (in this case B for the basins) and the
percentage of impervious area were developed using Figure 3.3. The Runoff Coefficient (C) was
then multiplied by the Rainfall Intensity (I) and the area of the calculated basin (A, in acres) to
determine the peak discharge. πΈπΈππ=πͺπͺπ°π°πͺπͺ ππππ=ππππππππ π·π·π·π·π·π·π·π·βππππππππ (π·π·πππ·π·) πΆπΆ=π π π π π π π π ππππ πΆπΆπ π πππππππ·π·π·π·π·π·πππ π πΆπΆ πΌπΌ=π π πππ·π·π π πππππ π π π πΌπΌπ π πΆπΆπππ π π·π·π·π·πΆπΆπΌπΌ (π·π·π π π·π·βπππ·π· ππππππ βπ π π π ππ) π΄π΄=π΄π΄ππππππ (πππ·π·πππππ·π·)
These peak flow values were used to calculate the size of the proposed detention and conveyance
structures, such as the drywell, inlets and pipes. The tables below contain the peak flows for
developed and undeveloped conditions for 5-year 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 6644.60 5156.50 77.60%0.540 5 3.29 0.27
2 4714.75 2360.10 50.06%0.350 5 3.29 0.12
3 344.50 0.00 0.00%0.080 5 3.29 0.00
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 6644.60 0.00 0.00%0.080 5 3.29 0.04
2 4714.75 0.00 0.00%0.080 5 3.29 0.03
3 344.50 0.00 0.00%0.080 5 3.29 0.00
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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 43% 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. Given the site and hillsides, above grade detention was not
feasible, so drywell locations were discussed early on.
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.
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. Several walkways were
designed with pervious pavers in mind to reduce impervious area.
Principle 4: Reduce runoff rates and volumes to more closely match natural conditions.
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 6644.60 5156.50 77.60% 0.650 5 6.33 0.63
2 4714.75 2360.10 50.06% 0.520 5 6.33 0.36
3 344.50 0.00 0.00% 0.350 5 6.33 0.02
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 6644.60 0.00 0.00% 0.350 5 6.33 0.34
2 4714.75 0.00 0.00% 0.350 5 6.33 0.24
3 344.50 0.00 0.00% 0.350 5 6.33 0.02
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All runoff from impervious surfaces on the property is collected and routed to BMP structures.
The infrastructure has been sized to capture the 100-year storm with full detention. The drywell
is designed to infiltrate storage capacity into the surrounding earth.
Principle 5: Integrate storm water quality management and flood control.
The proposed drywell will capture and treat runoff for water quality, and the drywell will infiltrate
the runoff into the soils, eliminating runoff from the site.
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. The drywell is proposed to be buried under the addition to the home so as to not be visible by
the public.
Principle 7: Use treatment train approach.
The design implements sheetflow across landscaping, pervious pavers, and sumps in the pipe
network 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.
Principle 9: Design and maintain facilities with public safety in mind.
The proposed design for driveway and walkways reduces ice buildup and dangerous conditions.
All grading was done with safety in mind, and no steep slopes occur on site.
4.0 Hydrological Criteria
4.1 Storm Recurrence and Rainfall
The property is not in the commercial core and is served by any city curb and gutter so this property
classifies as a βSub-urban area not served by public storm sewerβ. Due to this, the 5-year and
100-year events were analyzed.
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
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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. The storm systems were designed to route all impervious surfaces to the
drywells located onsite. The basins were delineated into sub-basins per the design points of
concentrations created by roof drains and inlets. Pipe networks were then created connecting the
sub-basins and conveying the flows to the overall point of concentration for the basin. The 100-
year peak flow for each sub-basin was calculated. Pipe sizes will be tested for hydraulic capacity
at 80 percent of their full flowrate for the permit submittal. Design charts giving Qdesign / Q full were
downloaded from FHWA and the equations in Section 4.8.4 will be used as the basis for these
calculations.
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 6644.60 5156.50 77.60%1.23 1 529 Drywell A
2 4714.75 2360.10 50.06%1.23 1 242 Drywell B
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5.1 5.1 Inlets
The 100-year peak flows were used in the sizing of inlets. Equations 4-17 to 4-20 from the URMP were
used in the analysis. They incorporate a 50% clogging factor and 40% opening in the grates. A water depth
of 0.04β was assumed and all the inlets were treated as sumps as they will be set a minimum of .04β(½
Inch) below the flow lines. Below is a summary of each square inlet being tested for capacity against their
tributary basin.
Below is a summary of each round inlet being tested for capacity against their tributary basin.
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 40.00 0.00 0.00% 0.350 5 6.33 0.00
1.2 62.50 0.00 0.00% 0.350 5 6.33 0.00
1.3 235.60 0.00 0.00% 0.350 5 6.33 0.01
1.4 235.00 0.00 0.00% 0.350 5 6.33 0.01
1.5 3246.00 2510.00 77.33% 0.650 5 6.33 0.31
1.6 175.00 175.00 100.00% 0.950 5 6.33 0.02
1.7 2650.50 2471.50 93.25% 0.820 5 6.33 0.32
2.1 47.25 0.00 0.00% 0.350 5 6.33 0.00
2.2 102.00 0.00 0.00% 0.350 5 6.33 0.01
2.3 93.50 0.00 0.00% 0.350 5 6.33 0.00
2.4 223.75 39.00 17.43% 0.430 5 6.33 0.01
2.5 1130.50 1130.50 100.00% 0.950 5 6.33 0.16
2.6 542.00 345.00 63.65% 0.570 5 6.33 0.04
2.7 238.00 19.00 7.98% 0.380 5 6.33 0.01
2.8 62.50 0.00 0.00% 0.350 5 6.33 0.00
2.9 117.50 0.00 0.00% 0.350 5 6.33 0.01
2.10 598.00 82.00 13.71% 0.400 5 6.33 0.03
2.11 104.00 9.50 9.13% 0.380 5 6.33 0.01
2.12 92.40 0.00 0.00% 0.350 5 6.33 0.00
2.13 91.40 0.00 0.00% 0.350 5 6.33 0.00
2.14 91.40 0.00 0.00% 0.350 5 6.33 0.00
2.15 349.30 349.30 100.00% 0.950 5 6.33 0.05
2.16 357.00 288.50 80.81% 0.700 5 6.33 0.04
2.17 474.25 97.30 20.52% 0.450 5 6.33 0.03
3.1 255.50 0.00 0.00% 0.350 5 6.33 0.01
3.2 89.00 0.00 0.00% 0.350 5 6.33 0.00
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)
A9-TRENCH DRAIN 1.6 175.00 175.00 100.00% 0.950 5 6.33 0.024 4" x 33.33'4 399.96 2.222 2.229 Yes
A13-TRENCH DRAIN 1.7 2650.50 2471.50 93.25% 0.820 5 6.33 0.316 4" x 36.20'4 434.4 2.413 2.421 Yes
B8-TRENCH DRAIN 2.6 542.00 345.00 63.65% 0.570 5 6.33 0.045 4" x 20.77'4 249.24 1.385 1.389 Yes
B20-TRENCH DRAIN 2.15 349.30 349.30 100.00% 0.950 5 6.33 0.048 4" x 16.33'4 195.96 1.089 1.092 Yes
B21-TRENCH DRAIN 2.16 357.00 288.50 80.81% 0.700 5 6.33 0.036 4" X 17'4 204 1.133 1.137 Yes
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5.2 5.2 Pipes
The pipes were analyzed by calculating the flow from the sub basins entering them. Below is table which
groups what sub basins are conveyed in each pipe. The TOC is below 5 minutes for all sub-basins, so a
reduction was not taken for the intensity. They were tested for hydraulic capacity at 80% of pipe
diameter. Depth of flow was also calculated in the spread sheets below. The pipes are all SDR 35 PVC with
a manningβs coefficient of .01.
Design Q design / Q full charts were downloaded from The Federal Highway Administration. The equations
in Section 4.8.4 was used as the basis for these calculations.
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)
A1-INLET 1.1 40.00 0.00 0.00%0.350 5 6.33 0.002 6" Round 6 0.039 0.046 Yes
A2-INLET 1.2 62.50 0.00 0.00%0.350 5 6.33 0.003 6" Round 6 0.039 0.046 Yes
A4-INLET 1.3 235.60 0.00 0.00%0.350 5 6.33 0.012 6" Round 6 0.039 0.046 Yes
A6-INLET 1.4 235.00 0.00 0.00%0.350 5 6.33 0.012 6" Round 6 0.039 0.046 Yes
A11-INLET 0.00 0.00 0.00%0.350 5 6.33 0.000 6" Round 6 0.039 0.046 Yes
B1-INLET 2.1 47.25 0.00 0.00%0.350 5 6.33 0.002 6" Round 6 0.039 0.046 Yes
B2-INLET 2.2 102.00 0.00 0.00%0.350 5 6.33 0.005 6" Round 6 0.039 0.046 Yes
B3-INLET 2.3 93.50 0.00 0.00%0.350 5 6.33 0.005 6" Round 6 0.039 0.046 Yes
B6-INLET 2.4 223.75 39.00 17.43%0.430 5 6.33 0.014 6" Round 6 0.039 0.046 Yes
B9-INLET 2.7 238.00 19.00 7.98%0.380 5 6.33 0.013 6" Round 6 0.039 0.046 Yes
B10-INLET 2.8 62.50 0.00 0.00%0.350 5 6.33 0.003 6" Round 6 0.039 0.046 Yes
B11-INLET 2.9 117.50 0.00 0.00%0.350 5 6.33 0.006 6" Round 6 0.039 0.046 Yes
B14-INLET 2.10 598.00 82.00 13.71%0.400 5 6.33 0.035 6" Round 6 0.039 0.046 Yes
B15-INLET 2.11 104.00 9.50 9.13%0.380 5 6.33 0.006 6" Round 6 0.039 0.046 Yes
B17-INLET 2.12 92.40 0.00 0.00%0.350 5 6.33 0.005 6" Round 6 0.039 0.046 Yes
B18-INLET 2.13 91.40 0.00 0.00%0.350 5 6.33 0.005 6" Round 6 0.039 0.046 Yes
B19-INLET 2.14 91.40 0.00 0.00%0.350 5 6.33 0.005 6" Round 6 0.039 0.046 Yes
C4-INLET 0.00 0.00 0.00%0.350 5 6.33 0.000 6" Round 6 0.039 0.046 Yes
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Storm System Pipes
Pipe System Pipe Contibuting Sub-Basins Design Flow Rate
Qdes
A A1 1.1 0.00
A2 1.2 0.00
A3 1.1,1.2 0.01
A4 1.3 0.01
A5 1.3 0.01
A6 1.4 0.01
A7 1.5 0.31
A8 1.5 0.31
A9 1.6 0.02
A10 1.5,1.6 0.33
A11 0.00
A12 1.5,1.6 0.33
A13 1.5-1.7 0.65
B B1 2.1 0.00
B2 2.1,2.2 0.01
B3 2.1-2.3 0.01
B4 2.1-2.3 0.01
B5 2.1-2.3 0.01
B6 2.1-2.4 0.03
B7 2.5 0.16
B8 2.5,2.6 0.20
B9 2.7 0.01
B10 2.7,2.8 0.02
B11 2.5-2.9 0.22
B12 2.1-2.9 0.25
B13 2.1-2.9 0.25
B14 2.10 0.03
B15 2.1-2.11 0.29
B16 2.1-2.11 0.29
B17 2.1-2.12 0.29
B18 2.1-2.13 0.30
B19 2.1-2.14 0.30
B20 2.1-2.15 0.35
B21 2.16 0.04
B22 2.16 0.04
B23 2.1-2.16 0.39
B24 2.17 0.03
B25 2.17 0.03
B26 2.17 0.03
B27 2.1-2.17 0.42
B28 2.1-2.17 0.42
B29 2.1-2.17 0.42
B30 2.1-2.17 0.42
B31 2.1-2.17 0.42
B32 2.1-2.17 0.42
C C1 3.1 0.01
C2 3.1 0.01
C3 3.1,3.2 0.02
C4 0.00
C5 3.1,3.2 0.02
C6 3.1, 3.2 0.02
C7 0.00
C8 0.00
C9 0.00
C10 3.1, 3.2 0.02
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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 0.00 2.00%0.01 0.05 0.58 4.0
A2 0.00 2.00%0.01 0.06 0.69 4.0
A3 0.01 10.00%0.01 0.05 0.61 4.0
A4 0.01 2.00%0.01 0.09 1.13 4.0
A5 0.01 2.00%0.01 0.09 1.13 4.0
A6 0.01 2.00%0.01 0.09 1.13 4.0
A7 0.31 2.00%0.01 0.32 3.81 6.0
A8 0.31 2.00%0.01 0.32 3.81 6.0
A9 0.02 2.00%0.01 0.12 1.47 4.0
A10 0.33 2.00%0.01 0.33 3.92 6.0
A11 0.00 2.00%0.01 0.00 0.00 4.0
A12 0.33 2.00%0.01 0.33 3.92 6.0
A13 0.65 2.00%0.01 0.42 5.04 6.0
B1 0.00 2.00%0.01 0.05 0.62 4.0
B2 0.01 2.00%0.01 0.08 0.95 4.0
B3 0.01 2.00%0.01 0.10 1.14 4.0
B4 0.01 2.00%0.01 0.10 1.14 4.0
B5 0.01 2.00%0.01 0.10 1.14 4.0
B6 0.03 15.00%0.01 0.09 1.04 4.0
B7 0.16 2.00%0.01 0.25 2.96 4.0
B8 0.20 2.00%0.01 0.27 3.25 4.0
B9 0.01 2.00%0.01 0.10 1.17 4.0
B10 0.02 2.00%0.01 0.11 1.27 4.0
B11 0.22 15.00%0.01 0.19 2.32 4.0
B12 0.25 15.00%0.01 0.20 2.42 4.0
B13 0.25 15.00%0.01 0.20 2.42 4.0
B14 0.03 2.00%0.01 0.14 1.68 4.0
B15 0.29 10.00%0.01 0.23 2.76 4.0
B16 0.29 10.00%0.01 0.23 2.76 4.0
B17 0.29 10.00%0.01 0.23 2.78 4.0
B18 0.30 10.00%0.01 0.23 2.79 4.0
B19 0.30 10.00%0.01 0.23 2.81 4.0
B20 0.35 10.00%0.01 0.25 2.97 4.0
B21 0.04 2.00%0.01 0.14 1.71 4.0
B22 0.04 2.00%0.01 0.14 1.71 4.0
B23 0.39 2.00%0.01 0.35 4.16 6.0
B24 0.03 2.00%0.01 0.13 1.61 4.0
B25 0.03 2.00%0.01 0.13 1.61 4.0
B26 0.03 2.00%0.01 0.13 1.61 4.0
B27 0.42 2.00%0.01 0.36 4.28 6.0
B28 0.42 2.00%0.01 0.36 4.28 6.0
B29 0.42 2.00%0.01 0.36 4.28 6.0
B30 0.42 2.00%0.01 0.36 4.28 6.0
B31 0.42 2.00%0.01 0.36 4.28 6.0
B32 0.42 2.00%0.01 0.36 4.28 6.0
C1 0.01 2.00%0.01 0.10 1.16 4.0
C2 0.01 2.00%0.01 0.10 1.16 4.0
C3 0.02 2.00%0.01 0.11 1.30 4.0
C4 0.00 2.00%0.01 0.00 0.00 4.0
C5 0.02 2.00%0.01 0.11 1.30 4.0
C6 0.02 2.00%0.01 0.11 1.30 4.0
C7 0.00 2.00%0.01 0.00 0.00 4.0
C8 0.00 2.00%0.01 0.00 0.00 4.0
C9 0.00 2.00%0.01 0.00 0.00 4.0
C10 0.02 2.00%0.01 0.11 1.30 4.0
Pipe Sizing
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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 0.00 4.0 2.00%3.2 0.01 0.087 0.351 0.01 0.00 0.00 Yes
A2 0.00 4.0 2.00%3.2 0.01 0.087 0.351 0.01 0.00 0.00 Yes
A3 0.01 4.0 10.00%3.2 0.01 0.087 0.784 0.01 0.00 0.00 Yes
A4 0.01 4.0 2.00%3.2 0.01 0.087 0.351 0.03 0.12 0.48 Yes
A5 0.01 4.0 2.00%3.2 0.01 0.087 0.351 0.03 0.12 0.48 Yes
A6 0.01 4.0 2.00%3.2 0.01 0.087 0.351 0.03 0.12 0.48 Yes
A7 0.31 6.0 2.00%4.8 0.01 0.196 1.034 0.30 0.41 2.43 Yes
A8 0.31 6.0 2.00%4.8 0.01 0.196 1.034 0.30 0.41 2.43 Yes
A9 0.02 4.0 2.00%3.2 0.01 0.087 0.351 0.07 0.20 0.80 Yes
A10 0.33 6.0 2.00%4.8 0.01 0.196 1.034 0.32 0.43 2.58 Yes
A11 0.00 4.0 2.00%3.2 0.01 0.087 0.351 0.00 0.00 0.00 Yes
A12 0.33 6.0 2.00%4.8 0.01 0.196 1.034 0.32 0.43 2.58 Yes
A13 0.65 6.0 2.00%4.8 0.01 0.196 1.034 0.62 0.63 3.78 Yes
B1 0.00 4.0 2.00%3.2 0.01 0.087 0.351 0.01 0.00 0.00 Yes
B2 0.01 4.0 2.00%3.2 0.01 0.087 0.351 0.02 0.08 0.32 Yes
B3 0.01 4.0 2.00%3.2 0.01 0.087 0.351 0.04 0.12 0.48 Yes
B4 0.01 4.0 2.00%3.2 0.01 0.087 0.351 0.04 0.12 0.48 Yes
B5 0.01 4.0 2.00%3.2 0.01 0.087 0.351 0.04 0.12 0.48 Yes
B6 0.03 4.0 15.00%3.2 0.01 0.087 0.960 0.03 0.12 0.48 Yes
B7 0.16 4.0 2.00%3.2 0.01 0.087 0.351 0.44 0.52 2.06 Yes
B8 0.20 4.0 2.00%3.2 0.01 0.087 0.351 0.57 0.60 2.40 Yes
B9 0.01 4.0 2.00%3.2 0.01 0.087 0.351 0.04 0.12 0.48 Yes
B10 0.02 4.0 2.00%3.2 0.01 0.087 0.351 0.05 0.16 0.62 Yes
B11 0.22 4.0 15.00%3.2 0.01 0.087 0.960 0.23 0.37 1.46 Yes
B12 0.25 4.0 15.00%3.2 0.01 0.087 0.960 0.26 0.38 1.52 Yes
B13 0.25 4.0 15.00%3.2 0.01 0.087 0.960 0.26 0.38 1.52 Yes
B14 0.03 4.0 2.00%3.2 0.01 0.087 0.351 0.10 0.24 0.94 Yes
B15 0.29 4.0 10.00%3.2 0.01 0.087 0.784 0.37 0.47 1.88 Yes
B16 0.29 4.0 10.00%3.2 0.01 0.087 0.784 0.37 0.47 1.88 Yes
B17 0.29 4.0 10.00%3.2 0.01 0.087 0.784 0.38 0.49 1.94 Yes
B18 0.30 4.0 10.00%3.2 0.01 0.087 0.784 0.38 0.49 1.94 Yes
B19 0.30 4.0 10.00%3.2 0.01 0.087 0.784 0.39 0.49 1.94 Yes
B20 0.35 4.0 10.00%3.2 0.01 0.087 0.784 0.45 0.52 2.06 Yes
B21 0.04 4.0 2.00%3.2 0.01 0.087 0.351 0.10 0.25 1.00 Yes
B22 0.04 4.0 2.00%3.2 0.01 0.087 0.351 0.10 0.25 1.00 Yes
B23 0.39 6.0 2.00%4.8 0.01 0.196 1.034 0.38 0.49 2.91 Yes
B24 0.03 4.0 2.00%3.2 0.01 0.087 0.351 0.09 0.24 0.94 Yes
B25 0.03 4.0 2.00%3.2 0.01 0.087 0.351 0.09 0.24 0.94 Yes
B26 0.03 4.0 2.00%3.2 0.01 0.087 0.351 0.09 0.24 0.94 Yes
B27 0.42 6.0 2.00%4.8 0.01 0.196 1.034 0.41 0.50 3.00 Yes
B28 0.42 6.0 2.00%4.8 0.01 0.196 1.034 0.41 0.50 3.00 Yes
B29 0.42 6.0 2.00%4.8 0.01 0.196 1.034 0.41 0.50 3.00 Yes
B30 0.42 6.0 2.00%4.8 0.01 0.196 1.034 0.41 0.50 3.00 Yes
B31 0.42 6.0 2.00%4.8 0.01 0.196 1.034 0.41 0.50 3.00 Yes
B32 0.42 6.0 2.00%4.8 0.01 0.196 1.034 0.41 0.50 3.00 Yes
C1 0.01 4.0 2.00%3.2 0.01 0.087 0.351 0.04 0.12 0.48 Yes
C2 0.01 4.0 2.00%3.2 0.01 0.087 0.351 0.04 0.12 0.48 Yes
C3 0.02 4.0 2.00%3.2 0.01 0.087 0.351 0.05 0.16 0.62 Yes
C4 0.00 4.0 2.00%3.2 0.01 0.087 0.351 0.00 0.00 0.00 Yes
C5 0.02 4.0 2.00%3.2 0.01 0.087 0.351 0.05 0.16 0.62 Yes
C6 0.02 4.0 2.00%3.2 0.01 0.087 0.351 0.05 0.16 0.62 Yes
C7 0.00 4.0 2.00%3.2 0.01 0.087 0.351 0.00 0.00 0.00 Yes
C8 0.00 4.0 2.00%3.2 0.01 0.087 0.351 0.00 0.00 0.00 Yes
C9 0.00 4.0 2.00%3.2 0.01 0.087 0.351 0.00 0.00 0.00 Yes
C10 0.02 4.0 2.00%3.2 0.01 0.087 0.351 0.05 0.16 0.62 Yes
Hydraulic Grade Line and Pipe Capacity
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Pipe Design Flow
Rate
Proposed Pipe
Diameter Slope d/D Manning
Coefficient Rh/D Hydraulic Radius Exit Velocity
(ID)Qdes (ft3/sec) Dpro(in)(%)(from Chart)n (from Chart)Rh (ft) = (Rh/D) Dpro V (ft/sec) = [1.49/n] Rh2/3 βS
A1 0.002 4.0 2.00%0.00 0.01 0.00 0.00 0.00
A2 0.003 4.0 2.00%0.00 0.01 0.00 0.00 0.00
A3 0.005 4.0 10.00%0.00 0.01 0.00 0.00 0.00
A4 0.012 4.0 2.00%0.12 0.01 0.08 0.08 3.76
A5 0.012 4.0 2.00%0.12 0.01 0.08 0.08 3.76
A6 0.012 4.0 2.00%0.12 0.01 0.08 0.08 3.76
A7 0.306 6.0 2.00%0.41 0.01 0.21 0.21 7.54
A8 0.306 6.0 2.00%0.41 0.01 0.21 0.21 7.54
A9 0.024 4.0 2.00%0.20 0.01 0.12 0.12 5.14
A10 0.331 6.0 2.00%0.43 0.01 0.23 0.23 7.81
A11 0.000 4.0 2.00%0.00 0.01 0.00 0.00 0.00
A12 0.331 6.0 2.00%0.43 0.01 0.23 0.23 7.81
A13 0.646 6.0 2.00%0.63 0.01 0.28 0.28 9.10
B1 0.002 4.0 2.00%0.00 0.01 0.00 0.00 0.00
B2 0.008 4.0 2.00%0.08 0.01 0.05 0.05 2.91
B3 0.012 4.0 2.00%0.12 0.01 0.08 0.08 3.76
B4 0.012 4.0 2.00%0.12 0.01 0.08 0.08 3.76
B5 0.012 4.0 2.00%0.12 0.01 0.08 0.08 3.76
B6 0.026 4.0 15.00%0.12 0.01 0.08 0.08 10.30
B7 0.156 4.0 2.00%0.52 0.01 0.25 0.25 8.43
B8 0.201 4.0 2.00%0.60 0.01 0.28 0.28 8.97
B9 0.013 4.0 2.00%0.12 0.01 0.08 0.08 3.76
B10 0.016 4.0 2.00%0.16 0.01 0.09 0.09 4.32
B11 0.223 4.0 15.00%0.37 0.01 0.20 0.20 19.59
B12 0.249 4.0 15.00%0.38 0.01 0.21 0.21 20.13
B13 0.249 4.0 15.00%0.38 0.01 0.21 0.21 20.13
B14 0.035 4.0 2.00%0.24 0.01 0.14 0.14 5.58
B15 0.290 4.0 10.00%0.47 0.01 0.24 0.24 18.20
B16 0.290 4.0 10.00%0.47 0.01 0.24 0.24 18.20
B17 0.295 4.0 10.00%0.49 0.01 0.24 0.24 18.37
B18 0.299 4.0 10.00%0.49 0.01 0.24 0.24 18.37
B19 0.304 4.0 10.00%0.49 0.01 0.24 0.24 18.37
B20 0.352 4.0 10.00%0.52 0.01 0.25 0.25 18.85
B21 0.036 4.0 2.00%0.25 0.01 0.15 0.15 5.86
B22 0.036 4.0 2.00%0.25 0.01 0.15 0.15 5.86
B23 0.388 6.0 2.00%0.49 0.01 0.24 0.24 8.21
B24 0.031 4.0 2.00%0.24 0.01 0.14 0.14 5.58
B25 0.031 4.0 2.00%0.24 0.01 0.14 0.14 5.58
B26 0.031 4.0 2.00%0.24 0.01 0.14 0.14 5.58
B27 0.419 6.0 2.00%0.50 0.01 0.25 0.25 8.36
B28 0.419 6.0 2.00%0.50 0.01 0.25 0.25 8.36
B29 0.419 6.0 2.00%0.50 0.01 0.25 0.25 8.36
B30 0.419 6.0 2.00%0.50 0.01 0.25 0.25 8.36
B31 0.419 6.0 2.00%0.50 0.01 0.25 0.25 8.36
B32 0.419 6.0 2.00%0.50 0.01 0.25 0.25 8.36
C1 0.013 4.0 2.00%0.12 0.01 0.08 0.08 3.76
C2 0.013 4.0 2.00%0.12 0.01 0.08 0.08 3.76
C3 0.018 4.0 2.00%0.16 0.01 0.09 0.09 4.32
C4 0.000 4.0 2.00%0.00 0.01 0.00 0.00 0.00
C5 0.018 4.0 2.00%0.16 0.01 0.09 0.09 4.32
C6 0.018 4.0 2.00%0.16 0.01 0.09 0.09 4.32
C7 0.000 4.0 2.00%0.00 0.01 0.00 0.00 0.00
C8 0.000 4.0 2.00%0.00 0.01 0.00 0.00 0.00
C9 0.000 4.0 2.00%0.00 0.01 0.00 0.00 0.00
C10 0.018 4.0 2.00%0.16 0.01 0.09 0.09 4.32
Exit Velocities
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5.3 Valley pan
The proposed valley pan located at the top of the driveway prevents runoff from the offsite basin from
flowing down the driveway. This offsite basin was analyzed to have a flow of 0.07 cubic feet per second
from a 100-year event, which was used to determine the necessary depth and slope of the structure. The
following page shows the report generated by Autocad Express, which was used to determine the capacity
of the valley pan.
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6.0 Proposed Facilities
This property is not connected to the COAβs storm water infrastructure, and the onsite drywells
are sized for full detention, as clarified in section 4.2 of this report. Below are the analyses for the
individual detention structureβs capacity and infiltration.
6.1 Drywell
Below is a table that shows the proposed drywells meeting the capacity required for full detention
of Basin 1 and 2.
7.0 Operation and Maintenance
7.1 Inlets and Piping
The piping must be maintained periodically to ensure proper operation. Minimum inspection
and maintenance requirements include the following:
β’ During the first year draw down should be checked for every event exceeding 0.25β of
precipitation to ensure no significant backups are occurring.
β’ Piping systems and sumps should be checked during and after storms routinely.
β’ After the first year, the system should be cleaned out at least once a year and more if the
first-year inspection proves more maintenance is required.
β’ More frequent cleaning reduces the amount of debris entering the system and reduces the
need for more intense maintenance.
β’ Clean the inside of any perforated pipes with a pipe cleaner accessed through cleanouts.
This should be done yearly, or as necessary if the system is not infiltrating properly or if the
system has become contaminated.
β’ Ensure heat tape is functioning before colder months to prevent damage to piping.
If the storm system is not maintained properly, replacement of parts or of the entire system may
be necessary.
7.2 Trench Drains and Slot Drains
Trench drains must be regularly inspected and maintained to prevent clogging and debris from
travelling further into the system. Routinely keep drain grates and surrounding patios clean and
free of leaves, dirt, and other debris. This will prevent clogging and damage to the storm
infrastructure. Inspect drain sumps quarterly and after every storm exceeding 0.5 inches,
remove excess sediment and debris buildup from the catch basin. Inspect system for damage
to the concrete and the grate. Inspect all grouted seams and cracks. If cracks are smaller than
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 16 8 452 85 537 529
Drywell B 2 6 8 4 226 42 269 242
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½β, record information and continue inspection regularly. If cracks are larger than ½β, regrout
and repair to prevent further damage. If grate is damaged, repair or replace as necessary.
7.3 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.
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.
7.4 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.
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