HomeMy WebLinkAboutFile Documents.122 W Main St.0032.2018 (14).ACBK122 West Main Street August 9, 2018
Drainage Report
for
122 West Main Street Avenue
Aspen, Colorado
Submitted To:
City of Aspen
Engineering Department
517 E. Hopkins St.
Aspen, CO 81611
Prepared by:
Sopris Engineering, LLC
502 Main Street Suite A3
Carbondale, Colorado 81623
SE Project Number: 17254
April 3, 2018
Revised August 9, 2018
08/23/2018
Reviewed by Engineering
12/04/2018 11:53:09 AM
"It should be known that this review shall not
relieve the applicant of their responsibility to
comply with the requirements of the City of
Aspen. The review and approval by the City is
offered only to assist the applicant's
understanding of the applicable Engineering
requirements." The issuance of a permit based
on construction documents and other data shall
not prevent the City of Aspen from requiring the
correction of errors in the construction
documents and other data.
122 West Main Street August 9, 2018
2 | P a g e
Table of Contents
A.Introduction ................................................................................................................................................. 3
B.Purpose of Report ....................................................................................................................................... 3
C.Project Location & Existing Site Description................................................................................................ 3
D.Project Summary......................................................................................................................................... 4
E.Existing Drainage Description ..................................................................................................................... 4
F.Post Drainage Description .......................................................................................................................... 4
G.Hydrologic Criteria ....................................................................................................................................... 6
H.Hydraulic Methods & Assumptions .............................................................................................................. 7
I.Water Quality Treatment & Detention Volume ............................................................................................ 8
J.Low Impact Design .................................................................................................................................... 11
K.Maintenance Plan ..................................................................................................................................... 12
L.Sediment and Erosion Control/Construction BMPs ................................................................................... 13
M.Conclusion ................................................................................................................................................ 14
N.Engineer’s Statement of Design Compliance ............................................................................................ 15
08/23/2018
122 West Main Street August 9, 2018
3 | P a g e
A. Introduction
This report has been prepared in support of the proposed improvements at 122 West Main Street Aspen,
Colorado. The information provided in this report will outline the overall onsite drainage mitigation concepts
resulting from the proposed development. Proposed improvements include a remodel of the entire interior
space, a new roof, ADA access ramp as well as the site and drainage improvements required to facilitate the
new construction. The requirements outlined with the City’s Urban Runoff Management Plan were used to
design the onsite stormwater infrastructure and water quality treatment Best Management Practices (BMPs).
B. Purpose of Report
Based on the location of this project and the proposed activity, the purposes of this Drainage Report are to:
• Comply with the City of Aspen’s Urban Runoff Management Plan (COA URMP) for a “Major Design”
project.
• Estimate existing and post development peak runoff rates for comparison to developed conditions
• Size post development stormwater mitigation infrastructure based on calculated post development
peak runoff rates and ensure allowable peak discharge rates do not exceed existing peak discharge
rates.
• Design and integrate water quality treatment facilities for the proposed onsite improvements
• Promote the City of Aspen’s 9 Principles to managing stormwater runoff where feasible given the
scope of the project and existing site constraints.
• Demonstrate that the proposed improvements will have no adverse impact to drainage on-site or
downstream of the site
C. Project Location & Existing Site Description
The existing property is approximately 13,500 square feet across Lots K, L, M, N and the west half of Lot O,
Block 58 of the original City and Townsite of Aspen. The existing property contains two buildings (122 and 132
West Main Street) connected by a lower level patio/light well. The existing Northstar Office Building (122) is
located on the eastern portion of the lot (across Lots N and O) and is the structure proposed for
redevelopment. No other improvements are proposed on Lots K, L or M.
A subsoil investigation and percolation test have been performed in support of this project by HP Kumar dated
February 5, 2018. The geotechnical study and boring results were used to determine the hydrologic
classification of the underlying soils and a field tested percolation rate of 1.1 min/in or approximately 55 in/hr
was determined, however an infiltration rate of 5 in/hr was used for this analysis.
The subject property falls within System 3 as described within the Surface Drainage Master Plan (SDMP) for
the City of Aspen, dated November 2001 prepared by WRC Engineering, Inc. The overarching approach to
the design of the stormwater mitigation is to provide drainage and water quality improvements that reduce the
overall impervious area of the existing site and to incorporate surface water quality treatment of stormwater
wherever possible; thereby reducing the development impacts on the City’s storm sewer system and
enhancing stormwater runoff that ultimately enters the Roaring Fork River.
08/23/2018
122 West Main Street August 9, 2018
4 | P a g e
According to FEMA Flood Insurance Rate Map panel number 08097C0203C with effective date of June 4,
1987, the property falls entirely within the Zone X flood hazard area. FEMA designates Zone X as areas
outside the 0.2% (500 year storm) annual chance floodplain. Additionally, the subject property lies outside of
the City’s Mud Flow Zones as depicted by Figure 7.1 of the URMP.
D. Project Summary
122 West Main intends to change the existing upper floor office to lodge units, and make some minor changes
to the exterior of the building. Changes include the construction of a third floor loft and associated dormers,
new deck construction on the north and south sides of the structure as well as new ADA access to a new front
entry of the building. Drainage and stormwater mitigation improvements are proposed to ensure the project
meets the “Major Design” project requirements of the COA Urban Runoff Management Plan. No improvement
west of 122 West Main Street, including the lower courtyard, are considered for this project. Therefore the
stormwater mitigation improvements outlined herein are limited to 122 West Main Street, which is consistent
with pre-design discussions with City Engineering Staff.
E. Existing Drainage Description
The existing site is primarily comprised of impervious roof area, from which stormwater runoff is collected
within a gutter system that appear to daylight to the surface at various points around the building. Existing
onsite basins were delineated to compare the runoff generated from the proposed site impervious areas to the
existing conditions. This analysis was utilized to calculate the existing peak discharge rates in order to provide
a comparison between existing and post development impervious areas as well as peak discharge runoff
rates.
Basin EX1 is an existing onsite basin encompassing the northern portion of the site and associated roof
drainage. The basin is primarily comprised of impervious roof, asphalt parking and an exterior concrete
walkway. Roof drainage is primarily collected in a series of gutters and directed to the surface through various
downspouts. The traditional surface drainage pattern is to the north toward the Block 58 Alley and ultimately
into the City’s curb and gutter collection system within 1st Street.
Basin EX2 is an existing onsite basin encompassing the southern portion of the site and associated roof
drainage. The basin is primarily comprised of impervious roof and walkways, as well as pervious lawn area.
Runoff generated on the south side of the existing site appears to infiltrate through the grass lawn, or sheet
flow off the site towards the Highway 82 (Main Street) right of Way.
Existing peak runoff rates summarized in Table 1 of this report.
F. Post Drainage Description
After discussions with City Staff, it was determined that the area of interest for this study did not include the
shared lower level courtyard, or any other area west of the existing 122 West Main Street building, as the
proposed remodel improvements do not alter the existing building footprint or propose any site improvements
to the lower courtyard. The overall drainage mitigation approach for this project includes routing onsite
stormwater runoff to designated water quality treatment areas. In order to properly size and design the
drainage infrastructure the proposed site was broken into various on-site post development sub-basins.
08/23/2018
122 West Main Street August 9, 2018
5 | P a g e
Descriptions of these basins are provided below and are depicted in the Civil Plans attached for illustrative
support.
Basin 1 primarily encompasses the majority of the upper level roof drainage area associated with 122 West
Main Street. Basin 1 was divided into various sub basins (1a through 1f) in order to properly size stormwater
conveyance infrastructure and locate anticipated water quality treatment facilities. Runoff generated within the
basin is collected in roof gutters/downspouts and routed to a proposed drywell (DW-A) within the permeable
paver parking zone for water quality treatment. The proposed drywell has enough capacity to provide full
retention of the 100-year storm event associated with the tributary drainage basins, however a grated lid will
be installed.
Basin 2 is comprised of the northern portion of the site and primarily encompasses the onsite at grade parking
area adjacent to the Block 58 alley. Runoff from this basin will percolate through the permeable pavement
surface for water quality treatment and into the underlying granular soils. Runoff events in excess of the
permeable paver’s treatment capacity will sheet flow off the property to the north to the Block 58 alley and
follow existing drainage patterns. A concrete walkway is proposed on the east side of the building (Sub Basin
2b) connecting the rear parking to the front entry. The east walkway replaces an existing concrete walkway
and matches existing grades and drainage patterns. Runoff from the sidewalk is collected in a landscape
swale and a series of landscape on the east side of the sidewalk. Collected runoff is then directed north to the
proposed drywell for water quality treatment.
Basin 3 primarily encompasses the southwestern portion of the upper level roof drainage area as well as the
elevated southern deck associated with 122 West Main Street. Basin 3 was divided into various sub basins (3a
through 3d) in order to properly size stormwater conveyance infrastructure and locate anticipated water quality
treatment facilities. Runoff generated within the basin is collected in roof gutters/downspouts and routed to a
proposed bioretention cell (BRC-A) within the existing front lawn, south of the proposed structure. Storm event
in excess of the bioretention cell’s design capacity will overtop the BRC and sheet flow across the front lawn
towards Main Street (Hwy 82), consistent with existing drainage patterns.
Basin 4 primarily encompasses the southern lawn and walkways associated with the front of the building.
Runoff generated within the basin follows existing drainage patterns by sheet flowing across the property to
the curb and gutter collection system within Main Street. A proposed permeable paver walkway to the front
entrance replaces the existing impervious brick walkway. The existing brick walkway on the west side of the
basin, which leads to the lower courtyard, will be regraded for ADA compliant access. Permeable pavers for
this area were deemed infeasible given the proximity of the existing trees and associated root zone. Therefore,
this path will be replaced in kind. The existing tree canopy was used when determining the effective
impervious area for this basin. . A concrete walkway is proposed on the east side of the building (Sub Basin
4b) connecting the rear parking to the front entry. The east walkway replaces an existing concrete walkway
and matches existing grades and drainage patterns. Runoff from the sidewalk is collected in a landscape
swale and a series of landscape on the east side of the sidewalk. Collected runoff is then directed north to the
proposed drywell for water quality treatment.
Developed peak runoff rates summarized in Table 1 of this report.
08/23/2018
122 West Main Street August 9, 2018
6 | P a g e
G. Hydrologic Criteria
The drainage criteria used for this study was based on the COA’s URMP dated December 2014. The
improvements associated with this project classify it as a “Major Design” which requires an analysis of the 10-
and 100-year storm events. This section describes the hydrological assumptions and methods used to
estimate these peak flow rates associated with the design storm events. Building Permit drawings have been
provided as an attachment for illustrative support of the proposed stormwater conveyance system and overall
grading plan.
Peak Runoff rates for the 10- and 100-year storm events were calculated using the Rational Hydrologic
Method (Eq. 1) since the cumulative total of basin areas was less than 90 acres.
Eq. 1: Q = C* I * A
Q = Runoff Flow Rate (cfs)
C = Runoff Coefficient
I = Rainfall Intensity (in/hr)
A= Area of Basin (acres)
The runoff coefficient (C) is a variable that represents the ratio of runoff to rainfall volumes during a storm
event. The determination of C mainly depends on the soil type, watershed impervious and storm event
frequency. Each drainage basin was studied to determine the percent of impervious area. Landscaping areas
were assumed to be 0% impervious or 0.15 and 0.35 for the 10- and 100-year runoff coefficients, respectively.
Roofs, patios and concrete areas were all assumed to be 100% impervious or 0.92 and 0.96 for the 10 and
100-year runoff coefficients, respectively. Areas with impervious areas different from 0% or 100% were
entered into UD-Rational Spreadsheets to determine the corresponding 10- and 100-year runoff coefficients.
UD-Rational Spreadsheet was developed by Urban Drainage Flood Control District (UDFCD).
The design rainfall duration used in the Rational Method is referred to as the time of concentration. The time of
concentration is the cumulative travel time, including overland flow and channelized flow, for runoff to get from
the furthest point upstream of a basin to a designated design point. Per COA URMP, 5 minutes was used as
the absolute minimum time of concentration. This minimum value was adopted for all of the delineated basins.
Two design points were taken for the proposed development in order to ensure peak runoff rates for the 10-
and 100-year storm events do not exceed existing conditions.
Design Point (DP-1) was established on the north side of the property and is consistent with the
existing drainage discharge location to the Block 58 Alley. Basin EX-1 was delineated in order to
determine the existing conditions peak runoff rates for the 10- and 100- year design storms. These
values are summarized in Table 1 below. Developed conditions Basin 1 and Basin 2 contribute runoff
to the design point and the peak runoff rates for the 10- and 100-year storm events can be found in
Table 2 and were primarily utilized in sizing onsite storm sewer conveyance pipes. It should be noted
that the proposed drywell has adequate storage capacity to fully retain the runoff volume from the 100-
year storm event for the contributory Basin 1. The 10- and 100-year runoff rates were therefore
excluded from the pre/post peak runoff comparison at DP-1. As a result, Block 58 Alley at DP-1
receives less peak runoff with the proposed construction as compared to existing conditions.
Design Point (DP-2) was established on the south side of the property and is consistent with the
existing drainage discharge location to Main Street. Basin EX-2 was delineated in order to determine
08/23/2018
122 West Main Street August 9, 2018
7 | P a g e
the existing conditions peak runoff rates for the 10- and 100- year design storms. These values are
summarized in Table 1 below. Developed conditions Basin 3 and Basin 4 contribute runoff to the
design point and the peak runoff rates for the 10- and 100-year storm events can be found in Table 2
below. The reduced onsite imperviousness combined with the proposed bioretention cell construction
results in less peak runoff to Main Street at DP-2 as compared to existing conditions.
Table 1: 10 & 100-yr Existing Drainage Basin Peak Runoff Summary
Table 2: 10 & 100-yr Post Improvement Basin Peak Runoff Summary
H. Hydraulic Methods & Assumptions
The post improvement drainage sub-basins described above were analyzed to verify the sizing of the
proposed stormwater conveyance systems proposed throughout the site. This section describes the hydraulic
methods and assumptions that were used to assist in the sizing of these stormwater infrastructure
improvements. Storm sewer pipes are utilized for hydraulic conveyance in this project. Supporting calculations
are provided within Appendix D of this report.
Storm Sewer sizing was achieved by using Manning’s equation (Eq. 2) to compute the flow rate in open
channels and partially full closed conduits. PVC SDR 35 pipe is proposed for all storm sewer conveyance
pipes and a Manning’s roughness coefficient of 0.013 was used. Storm pipes have been sized to
08/23/2018
122 West Main Street August 9, 2018
8 | P a g e
accommodate the peak runoff rates associated with a 100-year storm event contributory to the storm sewer
conveyance pipe. Table 3 below summarizes the design criteria utilized to size the storm sewer collection
mains. Hydraflow Software was used to determine flow depths and velocities for the analyzed pipes.
Supporting calculations and data for the street capacity analysis are provided within Appendix D.
Eq 2: Q = 1.49/n * (A/Pw)2/3 * A * S0.5
Q = Channel Capacity (cfs)
n = manning’s runoff coefficient (native: n = 0.027)
A = Area of flow (sf)
Pw = Wetted perimeter of channel (ft)
S = Channel longitudinal slope (ft/ft)
East Storm is located on the east side of the development property and collects roof drain downspout
drainage from Basins 1b through 1f, and conveys stormwater to the proposed Drywell located within
the permeable paver parking area.
West Storm is located on the west side of the development property and collects roof drain downspout
drainage from Basins 1a and 1c, and conveys stormwater to the proposed Drywell located within the
permeable paver parking area.
RG Storm is located on the west side of the development property and collects roof drain downspout
drainage from Basins 3a through 3c, and conveys stormwater to the proposed bioretention cell located
within the front lawn of the site.
Table 3: Storm Sewer Summary
Upon review of Table 3 all proposed drain pipes are sized to accommodate 100-year peak runoff rates
according to the design parameters required by the URMP. Support calculations are provided within Appendix
D of this report.
I. Water Quality Treatment & Detention Volume
Water quality treatment is required for all projects that disturb more than 200 square feet. The overall goal of
the water quality treatment requirements is to protect receiving waters including the Roaring Fork River,
Maroon Creek, Castle Creek and tributaries to these water ways. The treatment is provided by strategically
incorporating stormwater Best Management Practices into the project’s stormwater infrastructure that are
capable of providing full water quality treatment for up to the 80th percentile runoff event which corresponds to
the volume of runoff generated from a storm event with a magnitude falling between a 6-month and 1-year.
The water quality capture volume associated with these more common storm events is directly correlated to
the amount of impervious area within a contributing drainage basin.
08/23/2018
122 West Main Street August 9, 2018
9 | P a g e
The proposed solution to treat the runoff generated from the project’s imperviousness is to incorporate Low
Impact Design concepts and integrate permanent water quality treatment facilities such as drywell, permeable
pavers and a rain garden which are discussed in further detail below.
Dry Wells are a permanent structural BMP that incorporates manhole structures with perforated barrels at the
deeper depths. Washed screened rock is installed around the exterior of the perforated sections. When sub-
soils are capable of moderate to high infiltration rates, dry wells are considered to be a viable BMP. They
dramatically reduce the increased runoff and volume of stormwater generated from surrounding impervious
areas and promote infiltration; thereby improving the water quality of stormwater runoff. The dry well sizing
requirements outlined within Chapter 8 of the URMP were followed to determine the perforated area required
to treat the proposed roof area. The dry well proposed for this project is described in further detail below:
Dry Well (DW-A) is proposed to provide water quality treatment for post development drainage Basin
1. The proposed drywell is designed to have perforated barrels at the deeper depths with cleaned
screened rock around the exterior of the perforated sections. Runoff that is routed to the structure is
stored and allowed to infiltrate into the surrounding soils.
In addition to the providing water quality treatment capacity, the 10’ minimum drywell depth as
required by Chapter 8 of the URMP provides adequate storage volume to fully retain the runoff
generated by the 100-year, 1-hour storm event. The required storage volume for this design storm was
calculated using URMP Equation 3-2 and results in a required 144.4 cubic feet of storage based on
the contributory area and associated imperviousness. The proposed 10’ deep, 4’ diameter drywell
provides approximately 125 CF of storage volume within the drywell chamber alone, with an additional
34 cubic feet of storage capacity provided within the 1’ gravel backfill zone.
Vol Req. = P1,100* (1/12)* Impervious Area
Table 4: Drywell Retention Summary
A field tested average infiltration rate of 55 in/hr was estimated by the Geotechnical Engineer,
however a conservative value of 5 in/hr was used for this analysis. Table 5 summarizes the water
quality design results and supporting calculations are provide within Appendix E.
Rain Gardens (RG) are depressed landscaping areas designed to capture and filter or infiltrate the water
quality capture volume. Rain gardens utilize depressed zones within landscaping and incorporate the required
filter material set forth in Section 8.5.3 of the URMP. The water quality drainage basins for the proposed
improvements have been laid out based on the proposed building ridgelines to ensure the proposed receiving
rain garden is adequately sized to provide the required treatment volume. The water quality capture volume for
the respective BMP was calculated based on the criteria outlined within chapter 8 of the COA URMP.
RG-1 is located within the landscaping area directly south of the proposed building at 122 West Main
Street and is designed to provide water quality treatment for runoff from impervious roof and deck
areas within Basin 3. The rain garden utilizes the flat bottom for water quality treatment area, and the
08/23/2018
122 West Main Street August 9, 2018
10 | P a g e
required filter media is installed beneath the proposed plantings. Flows that exceed the capacity of
this facility will simply overtop the southern edge and will sheet flow across the front lawn, which will
offer additional water quality treatment. Flows will ultimately be routed to the curb and gutter system
within Main Street.
Permeable Pavers (PP) will provide water quality treatment for impervious areas located within Basin 2 as
well as the front entry and side yard walkways within Basin 2b and 4b. Given the close proximity to the
existing building foundation in Basin 2, an impermeable liner has been incorporated for a 10’ distance away
from the existing foundation. The underlying membrane will be sloped and direct percolated water away from
the foundation rather than infiltrating directly toward the foundation stemwall. Collected stormwater will then
permeate the underlying soils for water quality treatment consistent with a “full Infiltration” permeable
pavement design according to Chapter 8 of the URMP.
PP-Basin2a- A total of 600 SF of permeable pavers are proposed within Basin 2, replacing existing
concrete parking. No additional impervious areas are directed onto the permeable paver surface,
resulting in an impervious tributary area ratio of 0.0. A total effective imperviousness of 10% was
applied to the paver area based on a full infiltration section within Figure 8.28 of the URMP when
calculating peak runoff rates for the 10- and 100-year design storms. Water quality treatment is
provided through the URMP compliant construction given the impervious tributary area ratio is less
than the 2.0 maximum.
PP-Basin2b- A total of 131 SF of permeable pavers are proposed within Basin 2b, replacing existing
concrete sidewalk. No additional impervious areas are directed onto the permeable paver surface,
resulting in an impervious tributary area ratio of 0.0. A total effective imperviousness of 40% was
applied to the paver area based on a no-infiltration section within Figure 8.28 of the URMP when
calculating peak runoff rates for the 10- and 100-year design storms. Water quality treatment is
provided through the URMP compliant construction given the impervious tributary area ratio is less
than the 2.0 maximum
PP-Basin4a- A total of 46 SF of full infiltration permeable pavers are proposed within Basin 2,
replacing the existing brick entry walkway. No additional impervious areas are directed onto the
permeable paver surface, resulting in an impervious tributary area ratio of 0.0. A total effective
imperviousness of 40% was applied to the paver area to according to Figure 8.28 of the URMP when
calculating peak runoff rates for the 10- and 100-year design storms. Water quality treatment is
provided through the URMP compliant construction given the impervious tributary area ratio is less
than the 2.0 maximum.
PP-Basin4b- A total of 65 SF of permeable pavers are proposed within Basin 2b, replacing existing
concrete sidewalk. No additional impervious areas are directed onto the permeable paver surface,
resulting in an impervious tributary area ratio of 0.0. A total effective imperviousness of 40% was
applied to the paver area based on a no-infiltration section within Figure 8.28 of the URMP when
calculating peak runoff rates for the 10- and 100-year design storms. Water quality treatment is
provided through the URMP compliant construction given the impervious tributary area ratio is less
than the 2.0 maximum
Tree Canopy Credit will reduce the overall site imperviousness and provide water quality treatment for
regraded impervious brick walkway on the western portion of Basin 4 consistent with Section 8.4.1 of the
08/23/2018
122 West Main Street August 9, 2018
11 | P a g e
URMP. Tree canopies can considerably reduce stormwater runoff through the interception of direct rainfall and
root transpiration. An existing 11-ft radius coniferous tree that overhangs the existing brick walkway and has a
canopy area of 380 SF according to the survey provided. An impervious reduction credit of 114 SF (380 SF *
0.30) can therefore be applied to Basin 4. An existing 11-ft radius deciduous tree also overhangs the existing
brick walkway and has a canopy area of 380 SF according to the survey provided. An impervious reduction of
57 SF (380 SF * 0.15) can therefore be applied to Basin 4. Total basin imperviousness for Basin 4 is 110 SF.
Canopy Credit impervious reduction exceeds Basin 4 impervious area, therefore no additional water quality
treatment BMPs are required.
Table 5: Water Quality Treatment Volume Summary
*See Table 4 and Appendix for gravel volume calculation
J. Low Impact Design
Low Impact Design (LID) is a stormwater management strategy that aims to control stormwater at the source
by promoting infiltration, evaporation, filtering and detain runoff close to its source. The LID techniques that
have been incorporated into this project’s stormwater mitigation plan include: disconnecting impervious areas
where practical, reducing impervious areas, reducing peak runoff rates and volumes, and incorporating water
quality treatment facilities. Below is a list of the 9 Principles outlined within the URMP as well as the ways this
project has attempted to implement these principles.
• Principle #1-“Consider stormwater quality needs early in the design process”: SE was consulted
during the initial design process to provide drainage mitigation recommendations best as possible with
the proposed improvements. The results are the integration of permeable pavers, rain garden and a
drywell.
• Principle #2-“Use the entire site when planning for stormwater quality treatment”: The stormwater
mitigation approach for this project was somewhat limited by the existing site constraints. However
permeable pavers were integrated to replace existing impervious areas. A rain garden and a drywell
have been incorporated to provide water quality treatment for the impervious roof areas.
• Principle #3- “Avoid unnecessary impervious areas”: Efforts have been made to reduce impervious
areas whenever possible. This is evident with the permeable paver parking area, as well as the
permeable paver entry walkway, which are currently impervious.
• Principle #4- “Reduce runoff rates and volumes to more closely match natural conditions”: Runoff
rates and volumes have been reduced through the reduction of overall basin imperviousness and
natural conditions are mimicked through surface water infiltration via the permeable pavers, drywell
and rain garden.
08/23/2018
122 West Main Street August 9, 2018
12 | P a g e
• Principle #5- “Integrate stormwater quality management and flood control”: The proposed drywell and
reduced site imperviousness combine to provide stormwater treatment retention. The proposed
drywell has sufficient capacity to detain the 100-year storm volume for the contributory area. The
results are post development peak runoff rates that are less than existing levels.
• Principle #6- “Develop stormwater quality facilities that enhance the site, the community and the
environment”: The proposed bioretention cell provides a planting zone that can be landscaped
aesthetically. The implementation of permeable pavers reduces the amount of direct runoff compared
to existing conditions and promotes subsurface infiltration.
• Principle #7- “Use a treatment train approach”: Given the nature of the project being a remodel rather
than a scrape and replace, water quality mitigation treatment train opportunities were limited. However
the use of a bioretention cell in the front yard and permeable pavers in the rear parking, maintaining
existing tree canopy cover, and drywell detention/infiltration meet the intent of this principle.
• Principle #8- “Design sustainable facilities that can be safely maintained”: There are no risks
associated with maintaining the proposed BMPs. The proposed bioretention cell can be revegetated
upon sediment removal. The proposed drywell utilizes an access lid with inspection port in order to
reduce the drywell depth providing safer inspection conditions. A full maintenance plan has been
provided within Section K of this report.
• Principle #9- “Design and maintain facilities with public safety in mind”: The current drainage design
poses no risks to public safety.
K. Maintenance Plan
This section describes the stormwater management systems proposed for the project as well as the
associated maintenance anticipated with these improvements. All of the onsite stormwater mitigation
improvements will be owned and maintained by the property owner and the following maintenance program
should be followed to ensure proper functioning of the proposed improvements.
Dry Well: In the event the development stalls after Phase 1 infrastructure has been installed, inspection of this
structure should occur annually via the provided inspection port. Inspection and maintenance of the Phase 1
dissipation drywell is required at a minimum prior to the Phase 4 certificate of occupancy issuance. The
following may be required if debris and trash are compromising the infiltration capacity of the structure:
Remove sediment, trash and debris that is washed into them.
Verify that the dry well is infiltrating properly. This can be confirmed by inspecting the chamber 24
hours after a rainfall event. If standing water is encountered clogging should be further investigated
and remedied.
Replace the geo-fabric at the bottom and sides of the structure when it appears saturated with
sediment or infiltration time is slow. Replacement fabric should be attached to the concrete wall of the
dry well chamber.
Annually, after a large rain event or with a water hose, evaluate the drain-down time of the dry well to
ensure the maximum drain time of 24 hours is not being exceeded. If drain-down times are exceeding
the maximum, drain the dry well via pumping and clean out the percolation areas. If slow drainage
persists, the system may need to be replaced.
08/23/2018
122 West Main Street August 9, 2018
13 | P a g e
Bio-Retention Cell: Sediment build-up may require periodic removal of sediments and plants when clogging
reduces infiltration capacity to unacceptable levels. Plant materials in areas prone to sediment build-up should
be limited to grass and groundcovers tolerant of periodic wet-dry cycles.
Inspect detention area to determine if the sandy growth media is allowing acceptable infiltration. This
should be performed annually.
Occasional removal of weeds and unwanted vegetation will be required.
Remove debris and litter from detention area to minimize clogging of filter grow media.
The grow media will clog in time as materials accumulate on it. This layer will need to be removed and
replaced to rehabilitate infiltration rates, along with all turf and other vegetation growing on the surface.
This will be required every 5- 15 years, depending on infiltration rates needed to drain the WQCV in
12-hours or less.
Contractor to inspect all BRCs prior to Certificate of Occupancy and remove sediment as necessary
Permeable Pavers: After the installation of permeable paver, maintenance is relatively minimal but absolutely
critical to ensure the long lifetime of the system. The key maintenance objective for any permeable pavement
system is to know when runoff is no longer rapidly infiltrating into the surface, which is typically due to void
spaces becoming clogged and requiring sediment removal. This section identifies key maintenance
considerations for the Permeable Pavers.
Inspect pavement condition and observe infiltration at least once a year to ensure water infiltrates into
the surface. This can be done during a rain event or with a garden house. Video, photographs or
notes should be taken to help assess the infiltration degradation over time.
Debris should be removed, routinely, as a source control measure. Use a vacuum or regenerative air
sweeper to help maintain or restore infiltration as required. This should be done on a warm dry day for
best results. Do not use water with the sweeper. The frequency of sweeping is site specific and it
may be determined that biannual vacuuming is not necessary. After vacuuming pavers, replace infill
aggregate as needed.
In general pervious pavers do not form ice to the same extent as conventional pavements; therefore
sanding of these areas should not be needed. In fact, placing sand on the pervious pavers is not
recommended as it can reduce the infiltration capacity of the area. Snow shovels in lieu of mechanical
plows will be utilized to clear snow from the permeable paver area to avoid damaging the system.
When properly installed the system should not require much for repair/replacement. If a repair is
required, it is frequently due to poor placement of the paver blocks. Follow industry guidelines for
installation and replacement after underground repairs. If surface is completely clogged and rendering
a minimal surface infiltration rate, restoration of surface infiltration can be achieved by removing the
first ½ to 1 inch of soiled aggregate infill material with a vacuum sweeper. After cleaning, the voids
between the pavers will need to be refilled with clean aggregate infill material. Replacement of the
infill is best accomplished with push brooms.
L. Sediment and Erosion Control/Construction BMPs
Current practice standards provide parameters for mitigation of drainage and soil erosion activities relative to
site development. These parameters are referred to as best management practices (BMP’s). These BMP’s
are primarily grouped for two stages of the development, the construction phase and the post-development
phase, with the main emphasis on soil erosion and sediment transport controls.
08/23/2018
122 West Main Street August 9, 2018
14 | P a g e
During the construction phase for the proposed improvements the contractor will have to prepare and provide
a Construction Management Plan (CMP) that will address site erosions, dust control and disturbed ground
stability.
Final construction stages of work must follow a complete landscaping and ground covering task to
permanently re-vegetate and cover bear grounds that will remain open space to avoid long-term soil erosion.
This effort will reduce the risk of unnecessary degradation of the City’s drainage system. Temporary erosion
control structures installed during construction shall be left in place as necessary and maintained until new
vegetation has been re-established at a 70% level. Upon reaching a satisfactory level of soil stabilization from
the new vegetation, all erosion control structures shall be removed.
M. Conclusion
The proposed development incorporates stormwater and drainage mitigation strategies consistent with the
requirements of the current URMP. Overall site imperviousness is reduced by replacing existing asphalt with
permeable pavers, installing a bioretention cell to treat tributary roof drainage and removing an existing
concrete sidewalk on the east side of the property. Additional impervious area currently directing surface runoff
to the adjacent ROW will now be directed to the project’s drywell where water quality treatment and
stormwater detention will be provided.
08/23/2018
122 West Main Street August 9, 2018
15 | P a g e
N. Engineer’s Statement of Design Compliance
I hereby affirm that this report and the accompanying plans for the site drainage mitigation of the property
located at 122 Main Street was prepared under my direct supervision for the owners thereof in accordance
with the provisions of City of Aspen Urban Runoff Management Plan and approved variances and exceptions
listed thereto. I understand that it is the policy of the City of Aspen that the City of Aspen does not and will not
assume liability for drainage facilities by others.
________________________
Jesse K Swann, PE License No. 42787
08/23/2018
08/23/2018
08/23/2018
08/23/2018
08/23/2018
08/23/2018
08/23/2018
122 Main Street Major Design Drainage Study SE Project #17254
S OPRIS E NGINEERING • LLC
APPENDIX A
Urban Drainage Runoff Spreadsheets
10- and 100-yr Existing Conditions
08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =EX1
Area =0.039 Acres
Percent Imperviousness =98.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.88
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.86
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.86 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.13 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR EX1
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
EX-1-10YR.xls, Tc and PeakQ 4/2/2018, 1:31 PM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =EX1
Area =0.039 Acres
Percent Imperviousness =98.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.92
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.86
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.86 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.23 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR EX1
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
EX-1-100YR.xls, Tc and PeakQ 4/2/2018, 1:31 PM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =EX2
Area =0.036 Acres
Percent Imperviousness =53.8 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.42
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.37
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.37 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.06 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR EX2
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
EX-2-10YR.xls, Tc and PeakQ 4/2/2018, 1:31 PM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =EX2
Area =0.036 Acres
Percent Imperviousness =53.8 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.54
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.37
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.37 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.12 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR EX-2
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
EX-2-100YR.xls, Tc and PeakQ 4/2/2018, 1:32 PM08/23/2018
122 Main Street Major Design Drainage Study SE Project #17254
S OPRIS E NGINEERING • LLC
APPENDIX B
Urban Drainage Runoff Spreadsheets
10- and 100-yr Developed Conditions
08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =1a
Area =0.004 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.92
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.01 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-1a-10YR.xls, Tc and PeakQ 8/8/2018, 11:02 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =1b
Area =0.004 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.92
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.01 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-1b-10YR.xls, Tc and PeakQ 8/8/2018, 11:04 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =1d
Area =0.005 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.92
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.02 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-1d-10YR.xls, Tc and PeakQ 8/8/2018, 11:09 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =1e
Area =0.004 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.92
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.01 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-1e-10YR.xls, Tc and PeakQ 8/8/2018, 11:09 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =1f
Area =0.003 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.92
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.01 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-1f-10YR.xls, Tc and PeakQ 8/8/2018, 11:09 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =2a
Area =0.013 Acres
Percent Imperviousness =20.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.27
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.20
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.20 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.01 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-2a-10YR.xls, Tc and PeakQ 8/8/2018, 11:20 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =2b
Area =0.007 Acres
Percent Imperviousness =62.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.47
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.43
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.43 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.01 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-2b-10YR.xls, Tc and PeakQ 8/8/2018, 11:20 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =3a
Area =0.005 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.92
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.02 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-3a-10YR.xls, Tc and PeakQ 8/8/2018, 11:20 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =3b
Area =0.003 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.92
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.01 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-3b-10YR.xls, Tc and PeakQ 8/8/2018, 11:24 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =3c
Area =0.003 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.92
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.01 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-3c-10YR.xls, Tc and PeakQ 8/8/2018, 11:27 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =3d
Area =0.003 Acres
Percent Imperviousness =0.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.15
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.08
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.08 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.00 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-3d-10YR.xls, Tc and PeakQ 8/8/2018, 11:30 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =4a
Area =0.013 Acres
Percent Imperviousness =0.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.15
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.08
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.08 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.01 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-4a-10YR.xls, Tc and PeakQ 8/8/2018, 11:30 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =4b
Area =0.002 Acres
Percent Imperviousness =20.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =10 years (input return period for design storm)
C1 =64.50 (input the value of C1)
C2=9.00 (input the value of C2)
C3=0.983 (input the value of C3)
P1=0.77 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.27
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.20
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.20 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =3.71 inch/hr Peak Flowrate, Qp =0.00 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
10-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-4b-10YR.xls, Tc and PeakQ 8/8/2018, 11:30 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =1a
Area =0.004 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.96
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.02 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-1a-100YR.xls, Tc and PeakQ 8/8/2018, 11:35 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =1b
Area =0.004 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.96
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.02 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-1b-100YR.xls, Tc and PeakQ 8/8/2018, 11:37 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =1c
Area =0.006 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.96
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.03 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-1c-100YR.xls, Tc and PeakQ 8/8/2018, 11:43 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =1d
Area =0.005 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.96
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.03 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-1d-100YR.xls, Tc and PeakQ 8/8/2018, 11:39 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =1e
Area =0.005 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.96
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.03 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-1e-100YR.xls, Tc and PeakQ 8/8/2018, 11:44 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =1f
Area =0.003 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.96
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.02 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-1f-100YR.xls, Tc and PeakQ 8/8/2018, 11:41 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =2a
Area =0.013 Acres
Percent Imperviousness =20.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.44
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.20
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.20 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.04 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-2a-100YR.xls, Tc and PeakQ 8/8/2018, 11:45 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =2b
Area =0.007 Acres
Percent Imperviousness =62.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.57
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.43
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.43 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.03 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-2b-100YR.xls, Tc and PeakQ 8/8/2018, 11:48 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =3a
Area =0.005 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.96
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.03 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-3a-100YR.xls, Tc and PeakQ 8/8/2018, 11:48 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =3b
Area =0.003 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.96
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.02 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-3b-100YR.xls, Tc and PeakQ 8/8/2018, 11:49 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =3c
Area =0.003 Acres
Percent Imperviousness =100.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.96
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.90
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.90 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.02 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-3c-100YR.xls, Tc and PeakQ 8/8/2018, 11:49 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =3d
Area =0.003 Acres
Percent Imperviousness =0.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.35
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.08
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.08 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.01 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-3d-100YR.xls, Tc and PeakQ 8/8/2018, 11:51 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =4a
Area =0.013 Acres
Percent Imperviousness =0.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.35
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.08
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.08 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.03 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-4a-100YR.xls, Tc and PeakQ 8/8/2018, 11:51 AM08/23/2018
Project Title:
Catchment ID:
I.Catchment Hydrologic Data
Catchment ID =4b
Area =0.002 Acres
Percent Imperviousness =20.0 %
NRCS Soil Type =B A, B, C, or D
II.Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr =100 years (input return period for design storm)
C1 =100.10 (input the value of C1)
C2=10.70 (input the value of C2)
C3=1.080 (input the value of C3)
P1=1.23 inches (input one-hr precipitation--see Sheet "Design Info")
III.Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C =0.44
Overide Runoff Coefficient, C =(enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 =0.20
Overide 5-yr. Runoff Coefficient, C =(enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/Short Nearly Grassed
Type Meadow Field Pasture/Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations:Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey-Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.20 N/A 0.00 0.00
1
2
3
4
5
0 Computed Tc =0.00
Regional Tc =10.00
User-Entered Tc =5.00
IV.Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at Regional Tc, I =inch/hr Peak Flowrate, Qp =cfs
Rainfall Intensity at User-Defined Tc, I =6.29 inch/hr Peak Flowrate, Qp =0.01 cfs
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
122 MAIN STREET
100-YR
Paved Areas &
(Sheet Flow)
20
Shallow Paved Swales
DEV-4b-100YR.xls, Tc and PeakQ 8/8/2018, 11:51 AM08/23/2018
122 Main Street Major Design Drainage Study SE Project #17254
S OPRIS E NGINEERING • LLC
APPENDIX C
Water Quality BMP Calculations
08/23/2018
08/23/2018
122 Main Street Major Design Drainage Study SE Project #17254
S OPRIS E NGINEERING • LLC
APPENDIX D
Hydraulic Conveyance Structure Calculations
08/23/2018
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Friday, Mar 30 2018
EAST STORM
Circular
Diameter (ft) = 0.50
Invert Elev (ft) = 100.00
Slope (%) = 2.00
N-Value = 0.013
Calculations
Compute by: Known Q
Known Q (cfs) = 0.10
Highlighted
Depth (ft) = 0.12
Q (cfs) = 0.100
Area (sqft) = 0.04
Velocity (ft/s) = 2.75
Wetted Perim (ft) = 0.51
Crit Depth, Yc (ft) = 0.16
Top Width (ft) = 0.43
EGL (ft) = 0.24
0 1
Elev (ft)Section
99.75
100.00
100.25
100.50
100.75
101.00
Reach (ft)
08/23/2018
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Friday, Mar 30 2018
WEST STORM
Circular
Diameter (ft) = 0.50
Invert Elev (ft) = 100.00
Slope (%) = 2.00
N-Value = 0.013
Calculations
Compute by: Known Q
Known Q (cfs) = 0.06
Highlighted
Depth (ft) = 0.10
Q (cfs) = 0.060
Area (sqft) = 0.03
Velocity (ft/s) = 2.13
Wetted Perim (ft) = 0.46
Crit Depth, Yc (ft) = 0.12
Top Width (ft) = 0.40
EGL (ft) = 0.17
0 1
Elev (ft)Section
99.75
100.00
100.25
100.50
100.75
101.00
Reach (ft)
08/23/2018
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Monday, Apr 2 2018
RG STORM
Circular
Diameter (ft) = 0.50
Invert Elev (ft) = 100.00
Slope (%) = 1.00
N-Value = 0.013
Calculations
Compute by: Known Q
Known Q (cfs) = 0.07
Highlighted
Depth (ft) = 0.12
Q (cfs) = 0.070
Area (sqft) = 0.04
Velocity (ft/s) = 1.93
Wetted Perim (ft) = 0.51
Crit Depth, Yc (ft) = 0.13
Top Width (ft) = 0.43
EGL (ft) = 0.18
0 1
Elev (ft)Section
99.75
100.00
100.25
100.50
100.75
101.00
Reach (ft)
08/23/2018