HomeMy WebLinkAboutFile Documents.1350 Mountain View Dr.0027.2019 (2).ARBK
Drainage Report
1350 MOUNTAIN VIEW DRIVE
ASPEN, CO
81611
December 7, 2018
Prepared by
Adam Racette, P.E.
Roaring Fork Engineering
592 Highway 133
Carbondale, CO 81623
01/03/2019
Reviewed by Engineering
03/06/2019 8:47:01 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.
ii
Drainage Report
1350 MOUNTAIN VIEW DRIVE
ASPEN, CO
81611
I HEREBY AFFIRM THAT THIS REPORT FOR THE IMPROVEMENTS AT 1350 MOUNTAIN VIEW
DRIVE 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.
ADAM RACETTE, P.E.
RFE Project # 2017-43
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Table of Contents
1.0 General ................................................................................................................................. 4
1.1 Existing Site ..................................................................................................................... 4
1.2 Proposed Site .................................................................................................................... 4
1.3 Offsite Drainage ............................................................................................................... 5
2.0 Drainage Basins and Sub-basins .......................................................................................... 7
2.1 Drainage Basins................................................................................................................ 7
2.2 Peak Discharge Calculations ............................................................................................ 9
3.0 Low Impact Site Design..................................................................................................... 11
3.1 Principles ........................................................................................................................ 11
4.0 Hydrological Criteria ......................................................................................................... 13
4.1 Storm Recurrence and Rainfall ...................................................................................... 13
4.2 Storage Volumes Methodology ...................................................................................... 13
5.0 Hydraulic Criteria .............................................................................................................. 14
5.1 Inlets ............................................................................................................................... 14
5.2 Pipes ............................................................................................................................... 16
6.0 Operation and Maintenance ............................................................................................... 17
6.1 Pervious Paver Areas ..................................................................................................... 17
6.2 Drywell ........................................................................................................................... 18
6.3 Inlets ............................................................................................................................... 18
6.4 Trench Drains ................................................................................................................. 18
6.5 Swale .............................................................................................................................. 18
Appendices:
Appendix A – Geotechnical Investigation Report
Appendix B – HP Kumar Drywell Recommendations for Foundation Underdrain Letter
Appendix C – Hydrant Test Results
Appendix D – Drawings
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1.0 General
1.1 Existing Site
The residence of 1350 Mountain View Drive in Aspen, Colorado is located at the end of the
North Drive cul-de-sac on the east side of Cemetery Lane, north of Highway 82 within the City
of Aspen limits. The existing site contains an approximately 3,500 square foot home, a paved
turnaround driveway that extends into the ROW and existing vegetation including trees of
various sizes and native grasses and shrubs.
The parcel is surrounded by berms to the north and northwest. The Offsite topography from
Cemetery Lane to the west and the neighboring parcel to the southwest (1030 Cemetery Lane)
slope towards these berms and is routed to the highly vegetated area to the north and northeast of
the property, an aerial photograph is provided as Figure 2 further in the report. The historical
runoff from the 1030 Cemetery Lane is captured by a subtle swale on the west side of the
property and flows north to a low point south of the northern berm where water pools and travels
to the highly vegetated area to the northeast. These Offsite basins are considered in the analysis
of the drainage for 1350 Mountain View Drive. An existing conditions sheet is part of the
building permit set.
A geotechnical report was developed by HP Kumar dated September 6, 2017. A copy of the
geotechnical report is included in the submittal package. The geotechnical investigation of the
subsoils found below the topsoil and about 3 feet of mixed clay, sand and gravel fill, consist of
medium dense to dense, slightly silty sand above relatively dense, sand and gravel with cobbles
and probable boulders to the boring depths of 9 to 16 feet. No free water was encountered in the
borings at the time of drilling and the subsoils were moist to slightly moist with depth. Graphic
logs of the subsurface conditions encountered at the site are shown on Figure 2 of the
geotechnical report.
1.2 Proposed Site
This project is classified as a ‘Major Project’ per Table 1.1. of the URMP. The proposed
development is over 1000 square feet and disturbs an area of approximately 15,000 square feet,
roughly 90% 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 reconstruction of a two-story, single family residence
with a basement level and covered deck, driveway, and hardscape areas including a pathway
around the house and a walkway from the cul-de-sac. There are a number of plantings and
landscaped areas associated with this project as well. The proposed work reconstructs the
driveway entrance configuration and a walkway within the existing right-of-way but not beyond
the existing driveway limits within the cul-de-sac excluding the trenching of the existing right-
of-way for a water service tap. The topography of the parcel is relatively flat with berms to the
north and northwest of the property that divert the majority of offsite runoff.
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Design recommendations related to drainage include the implementation of a foundation drain
system and drywell specifications. Although free water was not encountered during exploration,
it is recommended that a foundation drain system be installed for local perched groundwater
during times of heavy precipitation or seasonal runoff. As such, foundation drain system around
the crawlspace areas and associated sump system have been proposed. Additionally, the drywell
design recommendations suggest installing drywells that have solid casings down to at least 2
feet below basement floor level with perforations below that level for drywells that are in close
proximity to the foundation as to not percolate directly into the building foundation.
This drainage report will focus on the onsite and offsite basins being collected and conveyed by
the proposed storm drainage systems. The final collection point for basins that are no longer
following historical runoff flow paths or experience a change in historical peak runoff is a
drywell designed for full detention of a 100-year storm event. The foundation drain and sump
system collects water and pumps excess water detained by the sump to a pipe daylighting to the
proposed west lawn swale as suggested by the geotechnical consultant.
1.3 Offsite Drainage
The Offsite basin east of Cemetery Lane and the neighboring parcel is referred to as Offsite
Basin C. Offsite Basin C continues its historical flow path to the highly vegetated area to the
northeast of the property via the swale on the west side of the property for its Sub-basin C1. Sub-
basin C2 directly flows to the low point to the south of the berm on the north side of the property
which ponds and flows to the highly vegetated area to the northeast. The proposed design
emphasizes the grading of a specified swale to ensure proper runoff of Offsite Sub-basin C1.
Offsite drainage captured in the North Drive cul-de-sac is referred to as Offsite Basin D and
accounts for the portion of the cul-de-sac that is sloped towards the property. This area is City of
Aspen right-of-way. The proposed storm drainage system design accounts for the North Drive
cul-de-sac runoff and detains it at the proposed onsite drywell.
The west lawn swale is the historical path for offsite runoff from the neighboring parcel (1030
Cemetery Lane) and a portion of offsite delineation to the northwest of the property; all
considered Offsite Basin C. In order to continue this historical path, a swale design is specified to
ensure sufficient runoff and a calculated depth of open channel flow. The total runoff to the
swale, as presented further in tables, is 1.70 cubic feet per second (cfs) with Offsite Basin C
contributing 1.46 cfs and Onsite Sub-basin B1 contributing 0.24 cfs of runoff during a 100-year
storm event.
A cross section detail of the 100-year storm event elevation in the designed swale is shown in
Figure 1.
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Figure 1: West Lawn Swale Profile
Site grading of the property will maintain this cross-section in order to properly route Offsite
drainage and continue the historical runoff flow path of the west side of the property. This
profile cross-section is included in the detail sheets within the plan set.
Figure 2: Aerial map of surrounding area. Offsite and western Onsite drainage continue to the highly vegetated area
northeast of the property (middle of subdivision).
The North Drive cul-de-sac does not currently have drainage collection. Since the proposed
scope of work involves work within the ROW such as reconstruction of the existing edge of road
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elevations, an effort is being made to collect the surface runoff at this location. The proposed
drainage system is referred to as Storm System D, which includes a trench drain at the driveway
entrance and a landscape inlet that collect runoff as part of the storm drainage system (Storm
System A). It is detained by Drywell A.
2.0 Drainage Basins and Sub-basins
The parcel’s basin, excluding the west lawn area, is considered a single onsite basin with a point
of concentration located at the proposed drywell, which can then be subdivided into smaller sub-
basins. Basin and Sub-basin delineations are shown on sheet C-102 and C-103. These sheets list
impervious areas, runoff coefficients, peak flows, and the required volume of runoff to be
detained. The sub-basins were created to calculate the concentrated flow from each impervious
area. These sub-basin peak flows were then used to size the proposed infrastructure.
2.1 Drainage Basins
Basin A is a major basin within the parcel and consists of the disturbed area for the home
reconstruction, driveway, path and walkways, and lawn areas. The basin has a total area of
12,218 square feet (sf) and is 27.57% impervious. Impervious sections of the basin include the
roof structure and landscape walls. The driveway and pathways are to be constructed of pervious
pavers. The remainder of the basin is made up of pervious landscaped areas that surround the
residence. This basin was divided into a total of 13 sub-basins.
Sub-basin A1, A2, A7, A8, A9, and A10 collect runoff from roof drains and are routed to
Drywell A for full detention.
Sub-basin A3 collects runoff from the southwest corner of the home in the area of the chiller
pad and utility meters. This landscape drain prevents additional runoff into the west lawn swale
and drains the area of the home where utilities are concentrated.
Sub-basin A4 collects runoff from the North Drive cul-de-sac and a portion of the front lawn
and walkway which is to be constructed with pervious pavers.
Sub-basin A5 is a small sub-basin for the onsite portion of offsite runoff from the cul-de-sac that
is collected by the driveway trench drain. The driveway is to be constructed with pervious
pavers.
Sub-basin A6 collects runoff from the front lawn and driveway as well as a portion of the
pathway around the house. The driveway and front lawn area is graded to direct flow to the
landscape drain adjacent to the turning radius as a low-point. The driveway is to be constructed
with pervious pavers.
All inlets connect into Storm System A that drains into a drywell located to the east of the
building. This drywell, Drywell A, is 6 ft. in diameter and is 15.5 feet deep (rim elevation to
sump elevation). The depth is based on the geotechnical design recommendation to allow
percolation below foundation level as a precaution. The drywell emergency overflow will follow
the historical flow path towards the highly vegetated area to the northeast.
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Basin B is the Onsite basin that consists of the west lawn where a swale exists and is 5,011 SF
with 0% impervious area. Grading and drainage is to remain on its historical path with a more
pronounced swale than pre-development. The Grading and Drainage is sheet C-202 and shows
the flow path and spot elevations along the west lawn to continue a slope of 0.005 ft/ft.
Sub-basin B1 is the onsite sub-basin that contributes runoff to the west lawn swale. It is worth
noting that there will be ample vegetation on the west side of the property with proper
consideration for implementing the designed swale.
Sub-basin B2 is the onsite sub-basin that directly flows into a low point south of the berm
located north of the property. This low point is a historical concentration point for the west lawn
swale and routes water to the highly vegetated area to the northeast of the property. This
historical runoff pattern will continue post-development.
Basin C is the Offsite major basin that consists of the vegetated areas east of Cemetery Lane and
the neighboring parcel (1030 Cemetery Lane). Historical peak flows will remain constant as
there is no development to offsite basins for this project and the historical path of this flow will
remain via the west lawn swale described previously.
Sub-basin C1 is an Offsite sub-basin mainly consisting of the neighboring parcel to the
southwest (1030 Cemetery Lane). Historical peak flows will remain constant as there is no
development to offsite basins for this project and the historical path of this flow will remain via
the west lawn swale described previously.
Sub-basin C2 is an offsite sub-basin that flows south from the northern berm to a low point on
the site. This low point is a historical concentration point for the west lawn swale and routes
water to the highly vegetated area to the northeast of the property. This historical runoff pattern
will continue post-development.
Basin D is the asphalt paved area of the North Drive cul-de-sac that is graded to flow toward the
property. The runoff from this basin is collected via a driveway trench drain and a landscape
drain that is located near the pavement edge in a low-point for collection to prevent ponding on
the front lawn.
Sub-basin D1 is a portion of the asphalt paved cul-de-sac that flows to a low point between the
pavement and the property. This low point will have a curb cut and landscape inlet within the
disturbance limits to collect runoff. Topography south of this sub-basin flows south and away
from the property.
Sub-basin D2 is a portion of the asphalt paved cul-de-sac that flows toward the property
driveway and is collected via a trench drain at the driveway entrance. Topography south of this
sub-basin flows south and away from the property.
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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).
𝑰= 𝟖𝟖.𝟖 𝑷𝟎
(𝟎𝟎+𝑻𝒅)𝟎.𝟎𝟓𝟎 (𝐶𝑛𝑛𝑎𝑛�ℎ𝑛𝑛 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.
𝑷𝒑=𝑪𝑰𝑨
𝑃𝑝=𝑃𝑒𝑎𝑘 𝐶�ℎ𝑛𝑐�𝑎𝑛𝑒𝑒 (𝑐𝑒𝑛)
𝐶=𝑃𝑛𝑛𝑛𝑒𝑒 𝐶𝑛𝑒𝑒𝑒�ℎ𝑐�ℎ𝑒𝑛𝑛
𝐼=𝑃𝑎�ℎ𝑛𝑒𝑎𝑘𝑘 𝐼𝑛𝑛𝑒𝑛𝑛�ℎ𝑛𝑦 (�ℎ𝑛𝑐�𝑒𝑛 𝑛𝑒𝑛 �𝑛𝑛𝑛)
𝐴=𝐴𝑛𝑒𝑎 (𝑎𝑐𝑛𝑒𝑛)
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.
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On-site 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)
A 12218.00 3445.00 28.20%0.230 5 3.29 0.21
B 5011.00 0.00 0.00%0.080 5 3.29 0.03
On-site 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)
A 12218.00 0.00 0.00%0.080 5 3.29 0.07
B 5011.00 0.00 0.00%0.080 5 3.29 0.03
On-Site 100 Year On-site 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)
A 12218.00 3445.00 28.20%0.460 5 6.33 0.82
B 5011.00 0.00 0.00%0.350 5 6.33 0.25
On-Site 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)
A 12218.00 0.00 0.00%0.350 5 6.33 0.62
B 5011.00 0.00 0.00%0.350 5 6.33 0.25
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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 25% impervious. The treatment train approach is used on all runoff to increase
water quality and percolation.
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. Multiple 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. The existing swale was incorporated into the site to collect the
vast majority of the offsite runoff.
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.
Principle 4: Reduce runoff rates and volumes to more closely match natural conditions.
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)
A1 798 798 100.00%0.950 5 6.33 0.11
A2 234 234 100.00%0.950 5 6.33 0.03
A3 246 25 10.16%0.400 5 6.33 0.01
A4 153 0 0.00%0.350 5 6.33 0.01
A5 713 76 10.66%0.400 5 6.33 0.04
A6 2198 0 0.00%0.350 5 6.33 0.11
A7 4953 0 0.00%0.350 5 6.33 0.25
A8 611 0 0.00%0.350 5 6.33 0.03
A9 825 825 100.00%0.950 5 6.33 0.11
A10 713 713 100.00%0.950 5 6.33 0.10
A11 774 774 100.00%0.950 5 6.33 0.11
B1 3828 0 0.00%0.350 5 6.33 0.19
B2 1183 0 0.00%0.350 5 6.33 0.06
C1 23386 3120 13.34%0.400 5 6.33 1.36
C2 1744 0 0.00%0.350 5 6.33 0.09
D1 668 668 100.00%0.950 5 6.33 0.09
D2 1724 1724 100.00%0.950 5 6.33 0.24
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All runoff from impervious surfaces on the property is collected and routed to a drywell. This drywell has
been sized to capture and infiltrate the WQCV and to fully detain the 100-year runoff volume.
Principle 5: Integrate storm water quality management and flood control.
The use of the existing swale and calculating its capacity for a more refined swale to collect
runoff and a drywell for storage acts to integrate water quality BMPs with flood control methods.
Principle 6: Develop storm water quality facilities that enhance the site, the community and the
environment.
The use of the drywell for water quality reduces the runoff of sediment and contaminants from
the site. This reduces the site’s effect on the community.
Principle 7: Use treatment train approach.
The use of a drywell serves as a treatment train that adds a level of treatment to storm water from
the site. The use of a swale for the offsite runoff provides a natural treatment train of surface
storm water runoff.
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. 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.
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4.0 Hydrological Criteria
4.1 Storm Recurrence and Rainfall
The property is located outside of the commercial core and isn’t served by any storm system so
this property classifies as a “Sub-urban area not served by public storm sewer”. 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. The below tables
summarize these calculations.
The drywell diameter and storage depth of Drywell A was selected to meet the required capacity
of the impervious runoff detention and to satisfy the Geotech recommendation to install drywells
that have solid casings down to at least 2 feet below basement floor level with perforations below
that level.
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)
A 14610 5837 39.95%1.23 1 598 Drywell A
Drywell Storage
Drywell Basins Diameter Storage Depth Internal Volume External (18" of Screened Rock) Volume Total Capacity Required Capacity
(Name)(#)D (ft)H (ft)π*H*(D/2)2) (ft3)0.3*π*H*((D/2)+1.5)2 - (D/2)2) (ft3)(ft3)(ft3)
Drywell A A 6 15.5 438 164 603 598
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5.0 Hydraulic Criteria
This property is not connected to the COA’s storm water infrastructure. All hydraulics are sized
for onsite infrastructure.
5.1 Inlets
Onsite Basin A was divided into sub-basins according to which inlet they discharged into and
additional flow from Offsite Sub-basins D1 and D2 were added to their respective collection
points. The peak flows for the 100-year event in each sub-basin were used as the flowrate to size
the proposed inlets. Equations 4.17 through 4.20 from the URMP were used in these
calculations. The equations incorporate a 50% clogging factor and assume a 40% 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.
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Sub Basin and Rectangular Inlet Calculations 1 Hour(P1)1.23m=40%Ys=.04 (Depress inlet by 0.04')Return Period100Cg=50%Co=0.65Inlet IDBasin IDTotal Area Imp. Area Impervious C ValueTime of ConcentrationIntensityQ MaxInlet TypeInlet WidthInlet LengthEffective Open Area (EQ. 4-20)Inlet Capacity (EQ 4-19)Has CapacitySee(D1)(ft2)(ft2)(%)(From Table) (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)RectangularWo (inches)Lo (inches)Ae=(1-Cg)mWoLoQ=CoAe√2gYs(Yes/No)TRENCH DRAIN-A4.2A5, D22437180073.86%0.62056.330.2190.33' x 18'42341.3001.304Yes01/03/2019
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5.2 Pipes
Pipes used for the storm system will be SDR35 PVC with a Manning’s coefficient (n) of 0.01.
The pipes were sized to accommodate peak flows for a 100-year event from all contributing sub-
basins. The below table lists the sub-basins that contribute to each section of pipe.
Pipe sizes were tested for hydraulic capacity at 80% 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 Contributing Sub-Basins Design Flow Rate
Qdes
A1.1 A1 0.11
A1.2 A1, A2 0.14
A1.3 A1-A3 0.16
A1.4 A1-A3 0.16
A1.5 A1-A3 0.16
A1.6 A1-A6 0.32
A2.1 A4, D1 0.10
A2.2 A4, A5, D1, D2 0.38
A2.3 A4-A6, D1, D2 0.49
A3.1 A8, A9 0.14
A3.2 A8, A9 0.14
A3.3 A8-A10 0.24
A3.4 A8-A11 0.35
A3.5 A8-A11 0.35
A3.6 A10 0.10
A3.7 A11 0.11
A3
A1
A2
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/K√S}3/8 Dreq (in) Dpro (in)
A1.1 0.11 4.00%0.01 0.19 2.28 4.0
A1.2 0.14 4.00%0.01 0.21 2.51 4.0
A1.3 0.16 2.00%0.01 0.25 2.96 4.0
A1.4 0.16 2.00%0.01 0.25 2.96 4.0
A1.5 0.16 2.00%0.01 0.25 2.96 4.0
A1.6 0.32 2.00%0.01 0.32 3.86 6.0
A2.1 0.10 2.00%0.01 0.21 2.50 4.0
A2.2 0.38 2.00%0.01 0.34 4.13 6.0
A2.3 0.49 4.00%0.01 0.33 3.99 6.0
A3.1 0.14 2.00%0.01 0.24 2.88 4.0
A3.2 0.14 2.00%0.01 0.24 2.88 4.0
A3.3 0.24 2.00%0.01 0.29 3.49 4.0
A3.4 0.35 2.00%0.01 0.33 4.00 6.0
A3.5 0.35 4.00%0.01 0.29 3.52 6.0
A3.6 0.10 4.00%0.01 0.18 2.18 4.0
A3.7 0.11 4.00%0.01 0.19 2.25 4.0
Pipe Sizing
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6.0 Operation and Maintenance
6.1 Pervious Paver Areas
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 BMP’s.
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 Dpro(in)S (%)Dpro*.8 (in)n
A (ft) = π
(Dpro/2)2 Qfull (ft3/s) = Qdes/Qfull (from Chart)d (in) = (d/D)*Dpro (Yes/No)
A1.1 0.11 4.0 4.00%3.2 0.01 0.087 0.496 0.22 0.35 1.40 Yes
A1.2 0.14 4.0 4.00%3.2 0.01 0.087 0.496 0.29 0.41 1.62 Yes
A1.3 0.16 4.0 2.00%3.2 0.01 0.087 0.351 0.45 0.52 2.06 Yes
A1.4 0.16 4.0 2.00%3.2 0.01 0.087 0.351 0.45 0.52 2.06 Yes
A1.5 0.16 4.0 2.00%3.2 0.01 0.087 0.351 0.45 0.52 2.06 Yes
A1.6 0.32 6.0 2.00%4.8 0.01 0.196 1.034 0.31 0.43 2.58 Yes
A2.1 0.10 4.0 2.00%3.2 0.01 0.087 0.351 0.28 0.41 1.62 Yes
A2.2 0.38 6.0 2.00%4.8 0.01 0.196 1.034 0.37 0.47 2.82 Yes
A2.3 0.49 6.0 4.00%4.8 0.01 0.196 1.462 0.34 0.45 2.70 Yes
A3.1 0.14 4.0 2.00%3.2 0.01 0.087 0.351 0.41 0.50 2.00 Yes
A3.2 0.14 4.0 2.00%3.2 0.01 0.087 0.351 0.41 0.50 2.00 Yes
A3.3 0.24 4.0 2.00%3.2 0.01 0.087 0.351 0.69 0.68 2.70 Yes
A3.4 0.35 6.0 2.00%4.8 0.01 0.196 1.034 0.34 0.45 2.70 Yes
A3.5 0.35 6.0 4.00%4.8 0.01 0.196 1.462 0.24 0.37 2.19 Yes
A3.6 0.10 4.0 4.00%3.2 0.01 0.087 0.496 0.20 0.34 1.34 Yes
A3.7 0.11 4.0 4.00%3.2 0.01 0.087 0.496 0.22 0.35 1.40 Yes
Hydraulic Grade Line and Pipe Capacity
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6.2 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:
• Inspect drywells at least four times a year and after every storm exceeding 0.5 inches.
• 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.
6.3 Inlets
Culvert and inlet must be inspected and maintained quarterly and after every storm exceeding
0.5 inches. All sediment and debris that has entered the system must be removed. Dispose of
sediment, debris, and any other waste material removed from the inlets. Inspect for any damage
to the system, and replace or repair as necessary to prevent further deterioration. If grate is
damaged, repair or replace as necessary. Inspect all grouted seams and cracks. If cracks are
smaller than ½”, record information and continue inspection regularly. If cracks are larger than
½”, regrout and repair to prevent further damage. Report all settling and deteriorating conditions
to the infrastructure.
6.4 Trench 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 ½”, record
information and continue inspection regularly. If cracks are larger than ½”, regrout and repair to
prevent further damage. If grate is damaged, repair or replace as necessary.
6.5 Swale
Inspect and maintain swale quarterly, along with after every storm exceeding 0.5 inches. After
seasonal snowmelt, check swale for damage from snow removal or erosion. Any damage to
vegetation, grading, or compaction must be repaired to prevent further erosion. Revegetate
damaged areas to original condition. Any debris, rocks, or trash must be removed from the
structure. The swale must be mowed a minimum of 4 times during the summer, and a fall
cleanup of the swale must occur prior to snowfall.
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