HomeMy WebLinkAboutDrainage MemorandumDrai Memorandum
To: Chris Bendon
From:Jesse K. Swann, PE
Date: Sept.5,2025
Re: Drainage Memo-Sweetwater Ranch Guest Cabin 3
Encl: Appendix
Sopris Engineering LLC (SE) has prepared this drainage memo in support of the Grading & Building permit application for a cabin
Iocated in Garfield County. The proposed residence is situated on Tract G-7, which encompasses 165.2 acres within the.SB35
Subdivision Exemption Plat. The SB35 Subdivision is a recently recorded subdivision consisting of several parcels, each exceeding
35 acres, all located within an active 2,659+ l- acre working ranch under common ownership.
This memo includes a description of the existing site conditions, proposed improvements, and the general approach to stormwater
routing, considering the open expansiveness of the ranch and sunounding area,
Section A'Existing Site Overview: \
The existing site is located approximately 1 mile west of Sweetwater Road, Access to this portion of the ranch is cunently available \
via a private gravel road that extends from Sweetwater Road through the ranch. The SB35 Subdivision is a working ranch that will a
continue operations involving cattle raising and hay production. lmprovements to the existing gravel access road, including an . N-
extension to serve the proposed residence and other structures have been reviewed and approved by the U.S. Army Corps of \ l
Engineers, Garfield County, and Eagle County. Additionally, design of the road has been coordinated and approved bythe Gvosum v
Fire District. .{
The surrounding topography consists of relatively hilly tenain, with slopes ranging from 10% lo 20%,generally trending down ([
gradient towards the east and noftheast. Vegetation in the area includes pinyon pine, Gambel oak, and sagebrush, along with ' \
cultivated pastures featuring several lateral irrigation ditches used for flood irrigation.
\...
Sweetwater Creek, located approximately 0,9 miles east of the proposed residence site (as the crow flies), is the ultimate receiving . S '
waterbody. Although Sweetwater Creek is not included in FEMA Flood lnsurance Rate Maps, floodplain studies conducted in \\
anticipation of futuie bridge crossings indicate that the 1O0-year floodway and floodplain remain confined near the ordinary high- *\
water mark, all of which are well below the proposed residential site. Surface runoff from the building site follows existing drainage \
patterns, which are conveyed over and through irrigated pastures and areas of parlially vegetated ground cover typical of high- ^Nelevation, arid environments, Figure 1 is provided to illustrate the proposed location of the residence and sunounding area. \
Figure 1-Aerial lmage of Site
:,: ,;.' , i.l, l ,-,.,: : i
5C2 lt4ain $t:eei. Suile A3, C:ocnrj*l*, e0 B'i623 978-7A4."*3aa
pg. 1
Section B'Proiect Overview:
The proposed prolect involves the construction of a cabin, attached carpoft, gravel driveway, covered patio, utility improvements,
and landscaping enhancements, The landscaping will be designed to complement the surrounding vegetation and will be irrigated
using water supplied from Beaver Reservoir, located approximately 0,5 miles west of the site on the SB35 Subdivision property.
Grading activities will be carefully planned to minimize disturbance to existing topography and vegetation, Cut and fill operations
will be conducted in accordance with best management practices (BMPs) to ensure erosion control and sediment containment
during construction. Temporary sediment control measures, such as sediment control logs and silt fences, will be implemented
around the site to prevent sediment migration from the development area and to protect existing watenvays and drainage courses,
Additionally, erosion and sediment control BMPs will be maintained throughout construction, with inspections conducted in
compliance with the State issued Storm Water Management Plan permit, regularly to ensure their effectiveness. Final grading will
be completed to promote positive drainage away from the residence, reducing the potential for ponding or sudace runoff issues.
After construction is complete, disturbed areas will be stabilized through landscaping and revegetation to prevent erosion and
establish permanent ground cover.
Section C-Post Development Drainaqe Analysis:
To ensure the proper sizing of the proposed stormwater mitigation infrastructure, the post-development site has been divided into
several drainage basins. The details of these drainage basins are outlined below:
Design Point 1 - Located at the northwest corner of the cabin, this point corresponds with the outfall of Swale 1 and receives
runoff from two tributary basins:
. Basin 1 : A small, narrow, arid basin originating along the previously permitted Beaver Reservoir Access Road. The ground
cover consists of native vegetation, and sufface runoff is directed toward Swale 1.
. Roof 1 : The shed roof of the cabin directs runoff towards the south side of the structure, ultimately flowing into Swale 1.
Design Point 2 - Situated along the eastern side of the site at the outfall of Culvert '1, this point receives runoff from the following
tributary basins:
. Basin 2: Located south of the proposed cabin, this basin conveys runoff toward Swale 2, The ground cover is primarily
native vegetation, with developed areas including gravel surfaces associated with sections of the access drive and the
previously permitted Beaver Reservoir Access Road.
. Basin 3: This basin directs runoff toward Culvert 1 and mainly comprises undisturbed native ground cover. Portions of
gravel from the access road also fall within this basin.
. Roof 2: A shed roof designed to discharge rainwater directly onto the ground, where it disperses via a gravel splash pad
before flowing into Swale 2.
. Roof 3: A sloped shed roof drains into an adjacent flat roof, where water is captured by an internal drainage system.
Collected flows are discharged via a downspout into Swale 2.
Section D-Hvdroloqic Methods and Assu mptions :
Post-development drainage areas were analyzed using the Rational Method (Equation 1) since the cumulative total of tributary
areas are less than 90 acres.
Equationl:Q=CxlxA
Q = Runoff Flow Rate (cfs); C = Runoff Coefficient
l= Rainfall Intensity (in/h1; A= Area of Basin (acres)
i*2 M:!n Sireei, S',:it* A3, e::"lantai* aa 81it: t7C-7*4-0311
pg.2
The runoff coefficient (C) represents the ratio of runoff volume to rainfall volume during a storm event. lts determination is influenced
by several factors, including soil type, the percentage of impervious area within the watershed, and the frequency of storm events,
Each drainage basin was analyzed to quantify its percentage of impervious area,
The effective impervious area for each basin was then used to derive a weighted runoff coefficient. A spreadsheet tool developed
by the Mile High Flood District (MHFD) of Denver, CO was used to calculate site-specific runoff coefficients. This tool allows for the
calculation of site-specific C values based on a Type C hydrologic soil classification and associated impervious area.
The MHFD spreadsheet, which is included in Appendix, also computes the time of concentration (Tc), the time it takes for runoff to
travel from the furlhest point upstream in a basin to the designated design point, accounting for both ovedand and channelized
flow. A minimum time of concentration of 5 minutes was adopted for the smaller developed basins, whereas a minimum time of
concentration of 10 minutes was used for non-developed basins. The Tc values were then used to estimate the corresponding 100-
year rainfall intensities based on N0AA rainfall data for the sunounding area.
Table 1, provided below, presents the areas, C values, Tc, intensities and resultant 100-year peak runoff rates for the post-
development drainage basins.
Table 1 - Post Development Peak 100.Year Runoff Rates
Table 1: Post Development Drainage Basin: Rational Method Summary
Drainage Basin lD Area
{ac)
Percent
lmperuious
Runoff
Coefficient, C Selected
Tc (min)
Rainfall
lntensity
(in/hr)
Peak
Flow, Q
(cfs)
100-yr 1 00-vr 100-vr
POST DEVELOPMENT OFFSITE BASINS
BASIN 1 0.308 5.3o/o 0.51 14 4.41 0.69
BASIN 2 1.057 8.6%o.52 13.9 4.43 2.44
BASIN 3 o.402 21-84/o 0.57 10 5.18 1.19
ROOF BASINS
ROOF-1 0.02 100,00/o 0.89 7.08 0.10
ROOF-2 0.03 'l0O.Oo/o 0.89 5 7.O8 0.20
ROOF-3 0.04 1OO.Oo/o 0.8s 5 7.08 o-25
Section E-Hvdraulic Methods and Assumptions:
The 100-year post-development peak runoff rates summarized in Table 1 were used to size the proposed stormwater conveyance
system, which includes one culved and two swales.
Culvert Sizinq: Hydraflow Express Extension was used to size the single culvert located beneath the ddveway, Hydraflow Express
employs an energy-based Standard Step methodology to estimate culvert flow capacities. For maintenance and efficiency
purposes, a minimum culveft diameter of 18 inches was adopted. The proposed culverl will be constructed from ADS N-12 smooth
interior pipe, utilizing a Manning's Roughness Coefficient of 0.013, which reflects the flow roughness characteristics of the pipe
material, A description of each culveft is summarized below.
Culvert 1 : ls an 18" ADS N-12 pipe located at the eastern end of the driveway and is designed to convey water from Swale 2
and Basin 3
To accurately estimate culveft capacity, flow increments of 0.25 cubic feet per second (cfs) were evaluated iteratively untiljust prior
to overtopping. These flow estimates were cross-referenced with the total 100-year peak runoff rate tributary to the culvert, Table
2 summarizes the tributary peak runoff rate, the corresponding culvert capacity based on size, depth, material, and slope.
Supporting calculations are provided in the Appendix.
r*2 iiiain $ir*et, 3u!t* ii3, ii:*:crriaie, et 31623 *7*-i*4-1311
pg, 3
Table 2-Culveft Sizinq Summarv
CUTVERT DESIGN SUMMARY
Culvert
ID
Tributary Drainage
Basin lD
Qrm
(cfs)
Size
(in)
Capacity
(cfs)
CULVERT 1
BASIN 2, BASIN 3, ROOF 2
& ROOF 3
4.07 11.5
Swale Sizing: Swales are proposed within the development to convey sudace runoff around the proposed development. Manning's
Equation (Equation 2)was used to estimate the dimensions of the proposed drainage swales, employing the 100-year peak runoff
rates associated with tributary basins in conjunction with the minimum and maximum proposed longitudinal slope for each swale.
Roughness coefficients were determined based on the intended treatment for each swale. Swale dimensions were inputted into
Hydraflow software accounting for maximum and minimum longitudinal slopes. A brief description of the proposed swales is
provided below:
z
Equation 2, Q - +(+)t A * si
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 longitudinalslope (ft/ft)
Swale 1: This swale is designed to intercept and convey both historic offsite runoff and post-development flows generated from
Basin '1 and Roof 1, lt conveys these flows along the western perimeter of the cabin where the concentrated flow will travel
-100ft before following natural drainage patterns.
Swale 2: Receiving runoff from Basin 2 and Roofs 2 and 3, this swale is designed to intercept both historic offsite drainage and
post-development flows. lt channels these waters along the southern edge of the driveway, ultimately discharging into Culvert
1.
A summary of the resultant swale analysis as performed with Hydraflow is provided in Table 3.
Table 3-Swale Sizinq Summarv
SWALE DESIGN SUMMARY
swAutD
SWALE #1
5WALE #2
Section F-Erosion Control:
Erosion control measures are essential to mitigate drainage issues and prevent soil erosion during construction activities, While
the responsibility for implementing these measures lies with the Contractor under the State-issued Stormwater Management Plan,
the following erosion control practices are minimum recommendations to help reduce sediment transpott and soil degradation.
qloo
lcFsl n VELOSTY
(ft/secl
Ftow
DEPTH
MIN. DEPTH
PRoVIDED {ftI FULr FLoW CAPACTTY (CFSICONTRIBUTING
EAS|NS
sLoPE (%)
2.42 o.33 15.7MIN. SLOPE 3.Oo/o
3.90 o.26
1.0
31.3MAX. SLOPE
BASIN 1, ROOF 1
12.o%
o.79 0.030
2-89 o.54 15.7MIN. SLOPE 3_OO%o-030
4.76 o.45
1.0
25.4MAX. SLOPE
BASIN 2, ROOF 2 &
ROOF 3 7.90%
2.89
1i;2 U;in.*lir=:l llr;!ii: iii.i, ii*ri:ri':;i=l;. i:il *lai2: *i* ii:4.11.:i'li
pg. 4
. Pre.Construction Measures; Before any clearing, grubbing, lot grading, or construction work begins, the contractor
shall establish temporary sediment control logs and/or embedded silt fencing around the anticipated limits of
disturbance.. Culvert Protection: Hay bales and sediment control logs should be placed at the inlets and outlets of all culvefis to
prevent sediment from contaminating the culverts prior to the establishment of vegetation.
. Topsoil Management: Topsoil designated for removal and reuse shall be stockpiled with sediment control logs or silt
fencing around their perimeters. lf stockpiles are to remain for more than 15 days, temporary seed should be applied
to prevent erosion and weed groMh.
. Ditch Control: lnstall sediment control logs within the flowline of ditches at appropriate intervals to reduce flow
velocities and capture sediment.. Site lnspections: The site must be inspected and recorded in accordance with the State issued SWMP. Silt deposits
behind silt fencing and sediment control logs should be regularly cleared to ensure the effectiveness of the erosion
control system. These inspections and maintenance activities must be documented in a logbook readily available for
inspection.. Vegetation Establishment: Seed and mulch shall be applied over disturbed cut and fill slopes, with watering as
necessary, to establish permanent vegetative ground cover.
. Slope Stabilization: Erosion control blankets and/or hydromulching shall be applied to all cut and fill slopes that exceed
a 3:'l slope ratio.. Vehicle Tracking Control: Vehicle tracking control devises shall be installed at the entrance to Sweetwater Road to
prevent tracking onto the public roadways.
Temporary erosion control measures installed during construction should remain in place and be maintained until new vegetation
is established aI a70ok growth level. Once soil stabilization is satisfactory, temporary erosion control structures may be removed.
Given the dynamic nature of construction sites, the final location and selection of BMPs shall be at the contractor's discretion. All
necessary permits must be acquired prior to the commencement of construction, and the criteria outlined in these permits must be
adhered to until the associated permits are closed,
Section clusions:
The drainage analysis indicates that the proposed improvements will not adversely impact the subject property or surrounding
areas, Offsite and onsite runoff will be appropriately managed via the proposed drainage system which has been sized to safely
convey the '10O-year storm event associated with the proposed development. Lastly, erosion control BMPs will be enforced prior
throughout construction in compliance with State issued SWMP permit,
For furlher questions or additional information, please feel free to contact me.
Prepared by: Jesse K. Swann, PE
Encl:
Exhibit A: Post Development Drainage Basin Delineation Map
NOAA Rainfall Depth Chaft
Hydraflow Culvert Hydraulic Calcs
Hydraflow Swale Capacity Calcs
Mile High Flood District Spreadsheet
42787
0Q-05-24$
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5C2 Li:in SLr*ei, St"i:le .+3, ea&*::e;ale , ile E:*:3 t7C-7il4-l:1:
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ENGINEERING LLC
SWEETWATER RANCH
GUEST CABIN 3
GARFIELD COUNTY, CO
REPORT EXHIBtr
2
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Precipitation Frequency Data Server https://hdsc.nws.noaa.gov/pfds/pfdslrintpage.html?1at-3 9.1551&lor=...
ffi ,ffiNOA,A Atlas 14, Volume 8, Version 2
Location name: Gypsum, Colorado, USA*
Latitude: 39.7551', Longitude: -107.1036'
Elevation: 6997 ft*"
* source: ESRI Maps** source: USGS
POINT PRECIPITATION FREQUENCY ESTIMATES
Sanja Perica, Deborah Martin, Sandra Pavlovic, lshani Roy, Michael St. Laurent, Carl Trypaluk, Dale
Unruh, lvllchael YeKa, Geoffery Bonnin
NOAA National Weather Service, Silver Spring, l\.4aryland
PE tabUa! IPE_graphteal I Maps_S_aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidenge interval:'-(in 1n_qh9-9,)1 ,
recurrence interval
Duration
2 5 10 25 50 100 200 500 1 000
0.135
108-0.171
0.'175 0.247
198-0.31
0.314 o.414 0.4s9 0.590 0.689 0.830 0.945
.320-0 1 .544-1
10-min 0.198
159-0.251
0.257 0.362 0.459 0.606 1.22 1.38
.468-0 796-1 I
15-min o.241 0.313 0.442 0.560 0.739 0.891 1.69
I .564 .571.-1 .07
30-min 0,304 0.400 0.561 0.699 0.894
.683-1.21
1.05 't.2'l 1.38
71
0.384 0.486 0.655 o.797 0.996
759-1.34
1.15 1.31 1.47
.00-2.1
1.8660-min .61 1
2-hr 0.465 0.573 0.750 0.896
717-1.
1 .10 1.25
938-1
1.41 1.57 1.
1 .17
78
721 .843-1 .01-1
3-hr 0.537 0.636 0.800 0.939
755-1.
1 .13 1.28
968-1
1.44 1.60 1.81 '1.97
17-0 .01 1 .27
6'hr 0.688 o.782 0.940 1.08 1.27 1.43
.09-1.91
1.60
17-2.1
't.77 2.O0 2.19
0.862 0.984 1.19 1.37 1.62
1.28-2.1
1.82 2.04 2.26
.59-3.'1
2.56 2.79
.84-4.1.4 tz-l .40-2 .51-2.
24-hr 1.06 1.22 1.48
.23-1.81
1.71 2.04
I -OJ-Z.O I
2.30 2.58 2.86 3.26 3.56
1 .02-1 79-3 .92-3
2-day {.30 1.48 1.78
.45-2.1
2.O5 2.44 2.76 3.09 3.44 3.93 4.32
1 .10-1 .24-1 71 1.97-3.1 6-3
3-day 1.47 1.68 2.O2 2.32 2.76 3.87 4.40 4.82
1.24-1 .42-2 I
1.62 1.84
.56-2.1
2.21 2.54 3.00 3.38 4.17 4.72
4-day .87 1
1.99
1.70-2.34
2.22 2.63 2.98 3.47 3.87 4.24 4.70 5.74
7-day .90-2 I
1 0-day 2.30 2.55 2.98 3.34 3.86 4.28 4.71 5.16 5.77 6.25
1.9A-2.19-3 18-4.
3.50 4.04 4.50 5.15 5.66 6.19 6.73
o2-8.
7.47 8.04
.60-1171.84 0.1
30-day 3.9{4.32 4.99 5.55 6.32 6.93 7.53 8.'t 4 8.96 9.58
71-13.75-4 .44 11-1 1
45-day 4.87 5.40
72-6.21
6.26 6.95 7.89 8.59
.00-10.4
9.27
.30- 11
9.95
.50-12.
10.8 11.5
.21 (7 1
5.71 6.36 7.38 8.20 9.26 10.0 10.8 11.5 12.4 't3.0
60-day 12-S 74-1 1-1 .51-1 17
1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confldence interval. The probability that precipitation frequency
estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at
upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid Pl\4P values.
Please refer to NOAA Atlas '14 document for more information.
1of 4
PF graphical
1011112024,10:16 AM
Gulvert Report
Hydraflow Express Extension for Autodesk@ Civil 3D@ by Autodesk, lnc.
GC3 DRIVEWAY GULVERT
lnvert Elev Dn (ft)
Pipe Length (f0
Slope (%)
lnvert Elev Up (ft)
Rise (in)
Shape
Span (in)
No, Barrels
n-Value
Culvert Type
Culvert Entranbe
Coeff. K,M,c,Y,k
Embankment
Top Elevation (ft)
Top Width (ft)
Crest Width (f0
= 7762.64
= 37.00
= 6.00
= 7764.86
= 18.0
= Circular
= 18.0
=l
= 0.013
= Circular Concrete
= Square edge w/headwall (C)
= 0.0098,2, 0.0398, 0.67, 0.5
= 7767,57
= 25.00
= 5.00
GG' WruY CU-VERT
Calculations
Qmin (cfs)
Qmax (cfs)
Tailwater Elev (ft)
Highlighted
Qtotal (cfs)
Qpipe (cfs)
Qovertop (cfs)
Veloc Dn (ft/s)
Veloc Up (ft/s)
HGL Dn (ft)
HGL Up (ft)
Hw Elev (ft)
HwlD (ft)
Flow Regime
Tuesday, 4u9 12 2025
= 10.00
= 12.00
= (dc+D)/2
.00
.71
.10
7764.04
7766.15
7767.51
1.76
lnlet Control
1
1
I
1
0
6
7
50
50
EdS)
1t4
46
ns
ns
36
?&6
?0tD
@s
n6@
6.S
@s
6.6
-rct
I
r
--
,,7 -
Ghannel Report
Hydraflow Express Extension for Autodesk@ Civil 3D@ by Autodesk, lnc.
SWALE 1 .3%
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Friday, Aug 22 2025
0.33
0.790
Triangular
Side Slopes (z:1)
Total Depth (ft)
lnvert Elev (ft)
Slope (%)
N-Value
Calculations
Compute by:
Known Q (cfs)
Elev (ft)
3.00
2.50
2.00
1.50
1.00
00
00
030
Known Q
= 0.79
_J
=l
00, 3.00
00
0.33
2.42
2.09
0.34
1.98
0.42
=l
=$-0
Section Depth (ft)
2.00
1.50
1.00
0.50
0.00
0 1 87654J2
,/
\7 ,/\
0.50
Reach (ft)
-0.50
Ghannel Report
Hydraflow Express Extension for Autodesk@ Civil 3D@ by Autodesk, lnc.
SWALE 1 .12%
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ftls)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Friday, Aug 22 2025
0.26
0.790
Triangular
Side Slopes (z:1)
Total Depth (ft)
lnved Elev (ft)
Slope (%)
N-Value
Calculations
Compute by:
Known Q (cfs)
Elev (ft)
3.00
2.50
2.00
1.50
1.00
= 3.00, 3.00
= 1.00
Known Q
= 0.79
00
030
1
1
0
00
0.20
3.90
1.64
0.34
1.56
0.50
Section Depth (ft)
2.00
1.50
1.00
0.50
0.00
0 1 654J2 7 8
,/\
\,/\
0.50
Reach (ft)
-0.50
Ghannel Report
Hydraflow Express Extension for Autodesk@ Civil 3D@ by Autodesk, lnc.
GC3 SWALE 1 GAPACITY
Triangular
Side Slopes (z:1)
Total Depth (ft)
lnvert Elev (ft)
Slope (%)
N-Value
-3
=f
=l
=1,
=Q
3.0000,
00
00
00
030
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ftls)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (f0
Wednesday, Sep 3 2025
1.00
15.65
3.00
5.22
6.32
1.00
6.00
1.42Calculations
Compute by:
Known Depth (ft)
Elev (ft)
3.00
2.50
2.00
1.50
1.00
Known Depth
= 1.00
Section Depth (ft)
2.00
1.50
1.00
0.50
0.00
6543210 7 8
\7
\,/
/
0.50
Reach (ft)
-0.50
Ghannel Report
Hydraflow Express Extension for Autodesk@ Civil 3D@ by Autodesk, lnc.
GC3 SWALE 1 CAPACITY 12%
Triangular
Side Slopes (z:1)
Total Depth (ft)
lnveft Elev (ft)
Slope (%)
N-Value
Galculations
Compute by:
Known Depth (ft)
Elev (ft)
3.00
2.50
2.00
1.50
1.00
00, 3.00
00
= 1.00
= 12.00
= 0.030
Known Depth
= 1.00
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Wednesday, Sep 3 2025
= 1.00
= 31.30
= 3.00
= 10.43
= 632
= 1.00
= 6.00
= 2.69
=J
=f
Section Depth (ft)
2.00
1.50
1.00
0.50
0.00
0 1 8765432
\7
,/\
/\
0.50
Reach (ft)
-0.50
Ghannel Report
Hydraflow Express Extension for Autodesk@ Civil 3D@ by Autodesk, lnc'
SWALE 2.3%
Triangular
Side Slopes (z:1)
Total Depth (ft)
lnvert Elev (ft)
Slope (%)
N-Value
Calculations
Compute by:
Known Q (cfs)
Elev (ft)
3.00
= 3.00,3.00
= 1.00
Known Q
= 2.89
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Friday, Aug 222025
54
890
87
30
42
57
24
71
=Q.
-2,
=Q.
=J.-3.
=Q.
=1.
=Q.
00
00
030
=l
=J
=Q
Section Depth (ft)
2.00
1.50
1.00
0.50
0.00
2.50
2.00
1.50
1.00
0 1 87b5432
7.\
-
\
0.50
Reach (ft)
-0.50
Ghannel Report
Hydraflow Express Extension for Autodesk@ Civil 3D@ by Autodesk, lnc.
swALE 2 - 7.9%
Triangular
Side Slopes (z:1)
Total Depth (ft)
lnveft Elev (ft)
Slope (%)
N-Value
=Q.
=1.
=Q.
= y't.
=).
=Q.
=).-0.
3.00= 3.00
= 1.00
1.00
7.90
0300.
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Friday, Aug 22 2025
45
890
61
76
85
57
70
80Calculations
Compute by:
Known Q (cfs)
Elev (ft)
3.00
2.50
2.00
1.50
1.00
Known Q
= 2.89
Section Depth (ft)
2.00
1.50
'1.00
0.50
0.00
4J20 5 876
-\l!7\
0.50
Reach (ft)
-0.50
Channel Report
Hydraflow Express Extension for Autodesk@ Civil 3D@ by Autodesk, lnc.
GC3 SWALE 2 CAPACITY 3%
Wednesday, Sep 3 2025
Triangular
Side Slopes (z:1)
Total Depth (ft)
lnveft Elev (ft)
Slope (%)
N-Value
Calculations
Compute by:
Known Depth (ft)
Elev (ft)
3.00
2.50
2.00
1.50
1.00
= 3.00, 3.00
= 1.00
Known Depth
= 1.00
= 1.00
= 15.65
= 3.00
= 5.22
= 6.32
= 1.00
= 6.00
= 1.42
= 1.00
= 3.00
= 0.030
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Section Depth (ft)
2.00
1.50
1.00
0.50
0.00
10 432 5 B76
7\
\,/
\
0.50
Reach (ft)
-0.50
Ghannel Report
Hydraflow Express Extension for Autodesk@ Civil 3D@ by Autodesk, lnc.
GC3 SWALE 2 CAPACITY 7,9%
Triangular
Side Slopes (z:1)
Total Depth (ft)
lnvert Elev (ft)
Slope (%)
N-Value
-2-rJ
=l
=f
=f
=Q
3.00
0
00
00
00
90
03
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (f0
Wednesday, Sep 3 2025
1.00
25.40
3.00
8.47
6.32
1.00
6.00
Calculations
Compute by:
Known Depth (ft)
Elev (ft)
3.00
2.50
2.00
'1.50
1.00
Known Depth
= 1.00
112.
Section Depth (ft)
2.O0
1.50
1.00
0.50
0.00
654320 7 8
7\
\,/
./
0.50
Reach (ft)
-0.50
channelized frravel) rlow Tlme Tlme ol Concentarion
c
ovedand 0nIial) Fbwrhe
t"{mln)
sr {nn}lr (mrn)l. (fi)
{n)
lopliona0
(fr)
(opllonal)q {nrn)
NRCS
q lmin)E (mln)
Srbcatchment Name
NRCS
Hydrologlc
100-y.Lenglh
! (n)
u/s
tn)
{odional}
ors Elevatlon
{n)
{oPtonaI)
0.6 7.0 1.b7 0.60 25.5326o,130 60EAS|N 1 c 5-3
230 n77 7765 0.05 7.O 1,60 2.40 26.1 82$0.14EASIN 2 c 8.60
55,00 0.05 7.0 1.57 0.59 22,6321.40 180 0.140EAS|N 3 c
ROOF I c 100.0
ROOF2 c 100.0
ROOF3 c 100.0
u=(0.39s(1.1-c_s) v(Li
))/(s_r0,33)
r_t=L_r/(60Ky'G-t) =
Lt/(50V_t)
Calculation of Peak Runoff using Rational Method
[compuledt]-c=Ll+Lt (selec@d q_c=max{t-minimun , min(computedLc , R€gional Lc )}tr il,ninimum= 5 (udan)
f tl-minimum= 10 (non-udan)
Q(./s)=clA
${esiond
tl-c=(26-ilD+ Lt/(60(r4i+e)