HomeMy WebLinkAboutDrainage MemorandumDrainage Memorandum
To: Chris Bendon
From: Jesse K. Swann, PE
Date: April 24, 2026
Re: Drainage Memo -Sweet Water Ranch Road 2 — New Leaf Lane
Encl: Appendix
This drainage memo has been prepared by Sopris Engineering (SE) to support the construction a new secondary egress
road (New Leaf Road) that connects Sweetwater Road to multiple building sites that are either currently under construction
or conceptualized for future development. The secondary egress road travels predominantly through Eagle County for the
first 2 miles, before entering Garfield County for the last 0.4 miles, ultimately terminating at the previously permitted Upper
Houser Loop Road. The proposed road provides a secondary means of egress per Eagle County requirements given the
number of structures proposed and served by Upper Houser Loop Road. Eagle County requires secondary egress roads to
be single lane road accessible to a passenger vehicle, at a minimum, maintained throughout the year. The proposed egress
road is not required for emergency vehicle or fire truck access. Emergency services access is provided by the previously
permitted Road 3 as depicted in Figure 1 below. The information provided within this drainage memo is specific to the
portion of the road residing within Garfield County. A Drainage Basin Delineation Exhibit (Exhibit A) is provided as an
attachment to illustrate the tributary drainage basins associated with the secondary egress road, along with summary peak
runoff rates tributary to the proposed culverts. Additionally, a Nationwide 14 Permit has been submitted to the Army Corps
of Engineers to confirm regulatory compliance regarding wetland disturbance. A copy of these approvals will be forwarded
to Garfield County once received.
Project Overview:
The proposed project involves construction of a new gravel secondary egress road that generally follows an existing two
track internal ranch road and across undeveloped rangeland within the subject property. The objective of the proposed
improvements is to provide a suitable secondary means of egress for the multiple structures in development in compliance
with Garfield and Eagle County regulations.
Site Overview:
The proposed access road is served from Sweetwater Road within Eagle County and crosses Sweetwater Creek. A
separate permit covers work in this area to include the construction of a new bridge over Sweetwater Creek. The proposed
road then climbs approximately 500 feet over two miles before crossing into Garfield County.
The overall topography within the surrounding area is relatively to moderately flat, with slopes ranging from 5% to 12% -
generally sloping toward the north and east. The existing surface is primarily comprised semiarid rangeland along with
cultivated pastures that feature several lateral irrigation ditches for flood irrigation. Pockets of pinyon, Gambel oak, and
sage, are sporadically present within the development area as well. The new road design accommodates existing irrigation
practices and concentrated stormwater runoff by elevating the road along pastureland or locating culverts at existing
defined drainage channels.
Sweetwater Creek, located at the entrance to the proposed road, serves as the ultimate receiving waterbody for upstream
development within the New Leaf Road access area. Although Sweetwater Creek is not included in any FEMA Flood
Insurance Rate Maps, floodplain studies conducted in anticipation of future bridge crossings indicate that the 100-year
floodway and floodplain remain confined near the ordinary high-water mark, well below the proposed roadway.
502 Main Street, Suite A3, Carbondale, CO 81623 970-704-0311
pg. 1
Figure 1: Aerial Image of Site
Hydrologic Analysis Methods & Assumptions:
Various culverts are necessary along -the proposed -access road to properly convey stormwater. runoff; hence, stormwater
modeling was carried out to size these culverts. The NRCS Technical Release-55 (TR-55) hydrologic method was utilized
via Storm and Sanitary Analysis (SSA) software for calculating runoff volume, peak runoff discharge, and other hydrologic
data for small watersheds.
The NRCS TR-55 method requires rainfall data, soil type, Time of Concentration (Tc) and an estimate of the Curve Number
(CN) to develop peak flow rates. In addition, the NRCS method can be used where the following criteria applies:
• Watershed area is greater than 0.1 acres and less than 25 mi2
• CN is 50 or greater
• Tc is greater than 0.1 hours and less than 10 hours
• The computed value of IaIP is between 0.1 and 0.5.
These parameters were checked during the analysis for each of the drainage basins and confirmed to comply with the
limitations associated with TR-55. This is noted within each of the drainage basin descriptions below.
Input Parameters:
• Rainfall Data: 100-year cumulative storm for Garfield County Colorado, with a total rainfall amount of 2.58 inches
using a SCS Type II 24-hr storm distribution was applied for the model's rain gauge. The rainfall depth was
referenced from NOAA Rainfall Depth Charts.
• Soil Type: Based on National Resource Conservation Service (NRCS) soil survey data, the area primarily consists
of hydrologic soil group C.
502 Main Street, Suite A3, Carbondale, CO 81623 970-704-0311
pg. 2
• Curve Number (CN): Weighted Curve Numbers (CNs) were established based on ground cover classifications and
a soil hydrologic classification of Type C. Ground cover classifications were determined through field inspections
and aerial drone imagery. The following Curve Numbers were assigned based on these parameters:
o Pasture, Grassland (Condition: Good): 74
o Sagebrush Range (Condition: Fair): 63
o Pinyon & Juniper (Condition: Fair): 73
o Gravel Roads: 89
o Development <50% grass cover: 86
• Time of Concentration (Tc): Aerial topography was referenced in support of estimating the time of concentration for
each of the drainage basins described below. It should be noted that sheet flow was limited to 300 linear feet.
The results of the TR-55100-yr peak discharge analysis for each of the drainage basins are summarized below:
Drainage Basin Descriptions:
The study area was divided into multiple drainage basins to route the design storm event through the development and size
proposed culverts. The basins are further described below:
Basin UH-3: 37.9 acres of mostly semi -arid range lands with scattered pinyon/juniper stands. This basin and
corresponding outlet culvert were originally analyzed and permitted through Garfield County with the Upper Houser
Loop Road study, and further refined with the Guest Cabin 2 permit (under construction). The proposed impervious
areas associated with Guest Cabin 2 are included in this basin to analyze downstream culverts.
Basin UH-6: 1.9 acres of predominantly irrigated pasture lands range land. This basin and corresponding outlet
culvert were originally analyzed and permitted Garfield County with the Upper Houser Loop Road study and is
currently under design for a future Community Barn. Impervious areas associated with the Community Barn have
been included in this basin analysis to analyze downstream culverts. Confirmation of design assumptions will be
made in support of future building permit application for the Community Barn.
Basin UH-5: 2.3 acres of predominantly irrigated pasture lands range land. This basin and corresponding outlet
culvert were originally analyzed and permitted in Garfield County with the Upper Houser Loop Road study and is
currently under design for a future Community Barn. Impervious areas associated with the Community Barn have
been included in this basin analysis to analyze downstream culverts. Confirmation of design assumptions will be
made in support of future building permit application for the Community Barn.
Basin MR-N: 1.44 acres of mostly semi -arid range lands and sagebrush. This basin and corresponding outlet
culvert were originally analyzed and permitted through Garfield County with the Upper Houser Loop Road study,
and further refined with the Main Residence permit (under construction). The proposed impervious areas
associated with the northern portions of the Main Residence design are included in this basin to analyze
downstream culverts.
Basin P18: 11.7 acres of primarily pasture and semi -arid rangelands and tributary portions of gravel ranch road.
Basin P19: 13.7 acres of primarily pasture and semi -arid rangelands and tributary portions of gravel ranch road.
502 Main Street, Suite A3, Carbondale, CO 81623 970-704-0311
pg. 3
Basin P20: 6.1 acres of primarily pasture and semi -arid rangelands and tributary portions of gravel ranch road.
The 100-year peak runoff rates for each basin are summarized below in Table 1
Table 1: 100-Year Peak Runoff Rates Summary
Drainage
Basin ID
Area
acres
Tc
min.
Weighted
CN
la
in
P
in
Ia/P
Ratio
0100
cfs
MR-N
2.21
10.0
89.00
0.25
2.58
0.10
4.65
P18
11.71
11.6
63.69
1.14
2.58
0.44
3.00
P19
13.70
25.2
68.29
1.11
2.58
0.43
4.31
P20
6.10
13.4
64.25
1.11
2.58
0.43
1.60
UH-3
37.90
97.8
71.23
0.81
2.58
0.31
6.29
U H-5
2.27
10.0
86.30
0.32
2.58
0.12
4.19
UH-6
1.90
10.0
86.32
0.32
2.58
0.12
3.51
Hydraulic Analysis Methods & Assumptions:
The peak runoff rates outlined in Table 1 were used to size the proposed culverts. Hydraflow Express Extension was
utilized to perform this analysis. Hydraflow Express employs an energy -based Standard Step methodology to estimate
culvert flow capacities. For maintenance and efficiency purposes, a minimum culvert diameter of 24 inches was adopted.
All proposed culverts will be constructed from ADS N-12 smooth interior pipes, utilizing a Manning's Roughness Coefficient
of 0.013, which represents the flow roughness characteristics of the pipe material.
To accurately estimate the capacities for each culvert, a flow increment of 0.25 cubic feet per second (cfs) was applied to
each culvert and evaluated until just prior to roadway overtopping. This value was cross referenced to the total 100-year
peak runoff rate assigned to each culvert based on its corresponding drainage basin.
Below is a brief description of each proposed culvert, with Table 2 summarizing the results of the sizing analysis:
• CULVERT #3: Located at the northeastern low point of Basin UH-3. This culvert was originally permitted and sized
with the Upper Houser Loop Road, and subsequently with the Guest Cabin 2, currently' under construction. Its
sizing is based on the peak flow associated with Basin-UH3 updated to include the impervious areas associated
with Guest Cabin 2.
• CULVERT #6: Located at the northern low point of Basin UH-5. This culvert was originally permitted and sized with
the Upper Houser Loop Road. Its sizing is based on the peak flow associated with Basin-UH5 with assumptions
made for impervious areas associated with the forthcoming Community Barn design.
• CULVERT #7: Located at the northern low point of Basin UH-6. This culvert was originally permitted and sized and
with the Upper Houser Loop Road. Its sizing is based on the peak flow associated with Basin-UH6 with
assumptions made for impervious areas associated with the forthcoming Community Barn design.
• CULVERT G1: Located at the northeastern low point of Basin P19. Its sizing is based on the peak flow associated
with Basin 19 along with tributary Basins UH-3 and UH-6.
502 Main Street, Suite A3, Carbondale, CO 81623 970-704-0311
pg. 4
• CULVERT G2: Located at the northeastern low point of Basin P20. Its sizing is based on the peak flow associated
with Basin 20.
• CULVERT HMS: Located at the northern portion of Basin P20. Its sizing is based on historic irrigation flows as
expressed by the Ranch Manager, matching the size of additional existing HMS ditch culverts throughout the
property.
Table 2 summarizes the peak runoff rates associated with each proposed culvert, along with their respective capacities
based on sizing, depths, material types, and slopes.
Table 2: Culvert Capacity Summary
Culvert Tributary Drainage Q100 Size Capacity
ID Basin ID cfs in cfs
CULVERT #3 *
UH-3
6.24
24
22.00
CULVERT #6 *
UH-5
4.18
18
16.80
CULVERT #7 *
UH-6
3.5
18
20.00
CULVERT G1
UH-3, UH-6, P19
6.39
24
37.25
CULVERT G2
P20
1.58
24
18.75
* Loop Road culvert previously permitted. Included to support basin routing
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 (SWMP), the following erosion control practices are minimum recommendations to help reduce sediment
transport and soil degradation.
Construction activities inevitably create a risk of soil erosion and offsite sediment transport, particularly during rain events.
To combat this, the contractor shall install and maintain the following Best Management Practices (BMPs) throughout the
construction phase:
• 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 culverts
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. If stockpiles are to remain for more than 15 days, temporary seed should be
applied to prevent erosion and weed growth.
• Ditch Control: Install sediment control logs within the flowline of ditches at appropriate intervals to reduce flow
velocities and capture sediment.
• Site Inspections: 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.
502 Main Street, Suite A3, Carbondale, CO 81623 970-704-0311
pg. 5
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 3:1 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 at a 70% 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.
Conclusions -
The drainage analysis indicates that the proposed access road improvements will not adversely impact the subject property
or surrounding areas. Onsite runoff will be appropriately managed via the designed storm channels and culverts. Erosion
control BMPs will be enforced prior to construction, with supplemental drainage reports prepared for future Site Plan and
Building Permit applications associated with further development on Sweetwater Ranch.
For further questions or additional information, please feel free to contact me.
O�: •`�E K Slyy' `S'F
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14:59:09-06'00'
Prepared by: Jesse K. Swann, PE
Encl: Exhibit A: Drainage Basin Delineation Map
NOAA Rainfall Depth Chart
SSA Input/output Data
Hydraflow Culvert Hydraulic Calcs
502 Main Street, Suite A3, Carbondale, CO 81623 970-704-0311
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BASIN ROUTING SCHEMATIC
SWEETWATER RANCH - ROAD 2 - NEW LEAF LANE
COUNTY OF GARFIELD, STATE OF COLORADO.
LEGEND UH3 uli6
XX DRAINAGE BASIN #3 #7
XX CULVERT
P19
XX DRAINAGE BASIN (EAGLE COUNTY)
O CULVERT (EAGLE COUNTY)
UH5 G1
##6 P17
P13
P18 E16
E15
P14
P20 P11 P10 P15 P12
P9 Pik)
G2 E13 E14 E10 Ell E12 E8 E9
P1 P2 P3 P4 P5 P6 P7
E1 E3 E5 E6
SWEETWATER CREEK
SOPRIS ENGINEERING LLC
502 MAIN STREET • SUITE A3•CARBONDALE CO 81623
(970) 704.0311 - soprisengineering.com
G:\2024\34008 SWEETWATER_RANCH\CIVIL\CIVIL DWGS\LXHIBITS\DRAINAGE\ROADS\34008 ROAD 2 DRAINAGE BASINS.DWG - Mar 24, 2026 - 3:17pm
Precipitation Frequency Data Server https://hdsc.nws.noaa.gov/pfds/pfds_printpage.html?lat=39.7551&ton=...
NOAA Atlas 14, Volume 8, Version 2
Location name: Gypsum, Colorado, USA*
Latitude: 39.7551°, Longitude:-107.1036'
Elevation: 6997 ft**t
'source: ESRI Maps
" source: USGS
POINT PRECIPITATION FREQUENCY ESTIMATES
Senja Penca, Deborah Martin, Sandra Pavlovic, Ishani Roy, Mchael St. Laurent, Carl Trypaluk, Dale
Unruh, Mchael Yekta, Geoffery Bonnin
NOAA, National Weather Service, Silver Spring, Maryland
PF tabular I PF graphical I Maps_8_aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1�
Average recurrence interval
ears
Duration
)^2 1 5
10 1 25 1 50
100 200 500 1000
(0249-0.403)I 0.320-0 588)' 0.373 0 694)
(0.424-0 847 0An-1 02 0.544128 0.598-1A7
(--- -
5-min 0.108-05 71)
(0.140-017- (0.198-0 316 •
0.198
0.257 0.362
0.459 0.606 0.731
--J
0.864 1.01 1.22 1.38
10-min
0.159-0.251);
0.206-0.326 .289-0.462)
0.365-0.589 (0.468-0.832 (0.646-1.02)
(0.621-124 050(.691-1.0.796-1.87 875-2.15
)
-min I
-,
0.313-&-
0.560 0.739 0.891
1.05 1.23 1.48 1.69
07-2 �1515(0.1-0306),�1.0398)0.35-00445-0)J
5
.2.
.71-1.02 .666-1240.757-1.510841.83I0.971-228
30-min 0 -30-47f
0.244-0.386)'
0.400 0.561
(0.320-0.508) (0.448-0.715)
F 0.699 ) 0.894 1,05
(0.554 0 897 0.683-1.21 0.780.1.44
1.21 1.38 1.60 1.78
0.8861.72) 0 938-2.03 1.04-2.45 1.13-2.76
1.86
0.384
60-min
9A
(0.390-0818);
0.523-0836) (0. 33.1.02 0.59--1634
0.855-1.58
0.935-1.85) (1. 02.16 1. 0-2.57j] 1.18-2.88Z
1.57 78
2-hr
0.465
0.378 0 585]j
.463-0 721 1
0.804 0 9a7) (0 0.89614) (0.843
0.938 1.89
1.01�96) (1.08-2.28)l 1.17-2.86 1.24-2.96)
3-hr
I
IF
0.800 1 1.13
11 1.28
1.44 1.81 1.97
60
229 1.20-2.69 1.273.00 !,
0.437.672
.517-0.7970.681.01
(0.755-1.19 (0.876-1A9
0.940 1.08 1.27
I
0.98-1.72
1.04-2.00 (m1
0782
6-hr
0688
(0.5006.537.8
-0.96960 )
_0.939
S0.9
.767-117)!O4-1.35 98-1.8
-1.91
1.17-2.19(1.24-2.52)(1.342. __ 1.423.28)
- -
-0.636
1.
12-hr
0 0.86 O, I
J
' 0.979-1A7 (1 123.6, 1.28 2?10)
1.40-2.40
1.51 276 1.59 3.17) (1.73 3672 1.844.13)
24-h r
0.868-1.29
-0.8-98
1.02-21 A8
1.2341881 1.41 2110 1. 30461
4.79.3.00
3.26
1.923.46 2.04 3 97 (223.4.67 1 2.375.20
2 33-410 2A8r172 (2.72 5357) 2.90-6 21
2-day
1. 031057
1.2441878 J
1.49 2815
2.05
1. 1-2.49)
410 (2: 63 5S�
1.97 3
3-day11
1. 4-41 78
1.42-2.00
1.70-2A3
1.84 2 80)
224-3.48 2A6.3.98
2.64-4.58 .8.18 .26 (306 818) 326.6.87
4-day
1.3761?92
1.568419
2.87 4 92 3.04 fi 63 3.30 6 59) 3.50 7.31
1.87?2 65
2: 3 3 05
4 3J6 2.67 4 30
2.441
7-day
70 2934
32".53 6 28 3. 2 7828) (3.93.8.04
(1
1.90 2?63
2. 4 3312
.52 3854
2.84-4.30-08.4.86
.45
r--1� i
5.84 4.09-7.89 4.30 8.6910dy(1.za210 2.130 2.�3528-396)i 3.1847)3.4535 3.64.6.05 3.81
_
8.04
3.17
20-day (2.753 68 3.02 4 07 3.48 4 71 _ 3.86528 4.27 625 (4. 8-6 98 4.8317.84 5.02 8 79 5.35- 0.1) (5.60
z f ) I ) s_ -i
30-day
(3. 0 4.51) (3.i5-0.99) (4.325.78 J 8 6A7 (62B 7260) 5.62 SA8 t5.90 9344) 56.IF 8 10.5 SA5-111.9) (6.715 3.0)
6.95
45-day (4_ 6 5.59) (4.72 64.87 .2 (5.45-7.21 �6.02-8.05� (6;58 9938) (7. 05 0_4)s7_3o211.5) (7.50�12.7 .6 �14.3) (8.09 5.4)
60-day 5.71 6.36 7.38 8.20 9.26 10.0 10.8 11.5 12.4 13.0
(5.02-6.53) (5tW-128 (6A"A7) (7.12-9A5) 7.74-10.9 8.21-12.0 (8.51-13:3) (8.69-14.6) (8.99-16.2) (9.22-17.4) i
Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).
lumbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence 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
ipper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.
'lease refer to NOAA Atlas 14 document for more information.
PF graphical
1 of 4 10/17/2024, 10:16 AM
Sweetwater Ranch Project
SSA Input/Output
Subbasin Hydrology
Subbasin: MR-N
Input Data
Area (ac)_.._.........................................
2.21
Peak Rate Factor ............ ._....................
484
Weighted Curve Number ............ .........
89
Rain Gage ID ............... „.„......................
Rain Gage-100yr
Composite Curve Number
32
Area Soil Curve
Soil/Surface Desaiption
(acres) Group Number
1.44 - 89
Composite Area & Weighted CN
1.44 89
Time of Concentration
TOC Method: SCS TR-55
Sheet Flow Equation:
To = (0.007 ` ((n ` Lf)A0.8)) / ((P^0.5) " (SfA0.4))
Where:
To = Time of Concentration (hr)
n = Manning's roughness
Lf = Flow Length (ft)
P = 2 yr, 24 hr Rainfall (inches)
Sf = Slope (ft/ft)
Shallow Concentrated Flow Equation :
V = 16.1345 " (SfA0.5) (unpaved surface)
V = 20.3282 • (SfA0.5); (paved surface)
V =15.0 " (SfA0.5) (grassed waterway surface)
V =10.0 " (SfA0.5) (nearly bare & untilled surface)
V = 9.0 ` (SP0.5) (cultivated straight rows surface)
V = 7.0 " (SfA0.5) (short grass pasture surface)
V = 5.0 • (SfA0.5) (woodland surface)
V = 2.5 ` (SfA0.5) (forest w/heavy litter surface)
To = (Lf / V) / (3600 sec/hr)
Where
To Time of Concentration (hr)
Lf = Flow Length (ft)
V = Velocity (ft/sec)
Sf = Slope (ft/ft)
Channel Flow Equation:
V = (1.49"(RA(2/3)) `(SfA0.5)) / n
R =Aq/Wp
To = (Lf / V) / (3600 sec/hr)
Where:
Tc = Time of Concentration (hr)
Lf = Flow Length (ft)
R = Hydraulic Radius (ft)
Aq = Flow Area (ft')
Wp = Wetted Perimeter (ft)
V = Velocity (ft/sec)
Sf = Slope (ft/ft)
n = Manning's roughness
User -Defined TOC override (minutes): 10
Subbasin Runoff Results
Total Rainfall (in) .................... ......... — 2.58
Total Runoff (in) .......„ ............................ 1.53
Peak Runoff (cfs)..................................- 4.65
Weighted Curve Number ....................... 89
Time of Concentration (days hh:mm:ss) 0 00:10:00
Page 1
Sweetwater Ranch Project
SSA Input/Output
Subbasin : P01
Input Data
Area(ac)................................................. 9.75
Peak Rate Factor .................:.................. 484
Weighted Curve Number....... .................. 72.73
Rain Gage ID .......................................... Rain Gage-100yr
Composite Curve Number
32 Area
Soil Curve
Soil/Surface Description (acres)
Croup Number
0.06
- 89
5.33
74
0.89
- 63
3.47
73
Composite Area & Weighted CN 9.75
72.73
Time of Concentration
Subarea
Subarea
Subarea
Sheet Ffow Computations
A
B
C
farming's Roughness
0.15
0
0
Flow Length (ft) :
300
0
0
Slope (%) :
25
0
0
2 yr. 24 hr Rainfall (in)
1.22
0
0
Velocity (ft/sec) :
0.36
0
0
Computed Flow Time (min) :
13.91
0
0
Subarea
Subarea
Subarea
Shallow Concentrated Flow Computation A
B
C
Flow Length (ft) :
821
82
0
Slope (%) :
17.66
1
0
Surface Type:
Grass pastureare & untille
Unpaved
Velocity (ft/sec) :
2.94
1
0
Computed Flow Time (min) :
4.65
1.37
0
Total TOC (min) ..................9.97
Subbasin Runoff Results
Total Rainfall (in) . 2.58
Total Runoff (in) ..................................... 0.6
Peak Runoff (cfs).................................... 7.52
Weighted Curve Number ........................ 72.73
Time of Concentration (days hh:mm:ss) 0 00:09:58
Page 2
Sweetwater Ranch. Project
SSA InpuUOutput
Subbasin : P18
Input Data
Area(ac)................................................. 11.71
Peak Rate Factor .................................... 484
Weighted Curve Number ........................ 63.69
Rain Gage ID .......................................... Rain Gage-100yr
Composite Curve Number
32
Area
Soil Curve
Soil/Surface Description
(acres)
Group Number
0.22
89
11.25
63
0.23
73
Composite Area & Weighted CN
11.7
63.69
Time of Concentration
Sheet Flow Computations
Manning's Roughness:
Flow Length (ft)
Slope (k) :
2 yr, 24 hr Rainfall (in)
Velocity (ft/sec) :
Computed Flow Time (min)
Shallow Concentrated Flow Computatior
Flow Length (ft)
Slope (k) :
Surface Type:
Velocity (fUsec) :
Computed Flow Time (min) :
Total TOG (min) ..................11.64
Subbasin Runoff Results
Subarea
Subarea
Subarea
A
B
C
0.15
0
0
300
0
0
17.3
0
0
1.22
0
0
0.31
0
0
16.12
0
0
Subarea
Subarea
Subarea
A
B
C
570 6% 0
22.8 6.4 0
Grass pastur6are & untille Unpaved
3.34 2.53 0
2.84 4.32 - 0
Total Rainfall (in) ..................................... 2.58
Total Runoff (in) ...................................... 0.29
Peak Runoff (cfs).................................... 3
Weighted Curve Number ........................ 63.69
Time of Concentration (days hh:mm:ss) 0 00:11:38
Page 19
Sweetwater Ranch Project
SSA Input/Output
Subbasin : P19
Input Data
Area(ac).................................................
13.7
Peak Rate Factor ....................................
484
Weighted Curve Number ........................
68.29
Rain Gage ID ..........................................
Rain Gage-100yr
Composite Curve Number
32 Area
Soil Curve
Soil/Surface Description (acres)
Group Number
0.33
89
5.69
74
7.55
63
0.14
73
Composite Area & Weighted CN 13.71
68.29
Time of Concentration
Subarea
Subarea
Subarea
Sheet Flow Computations
A
a
C
Manning's Roughness:
0.15
0
0
Flow Length (ft) :
300
0
0
Slope (%) :
14
0
0
2 yr, 24 hr Rainfall (in) :
1.22
0
0
Velocity (ft/sec) :
0.28
0
0
Computed Flow Time (min);
17.55
0
0
Subarea
Subarea
Subarea
Shallow Concentrated Flow Computation A
B
C
Flow Length (ft) :
1128
0
0
Slope (k) :
12.4
0
0
Surface Type:
Grass pasture Unpaved
Unpaved
Velocity (ft/sec) :
2.46
0
Computed Flow Time (min) :
7.64
0
Total TOG (min) .................25.19
1
Subbasin Runoff Results
Total Rainfall (in) ..................................... 2.58
Total Runoff (in) ...................................... 0.43
Peak Runoff (cfs).................................... 4.31
Weighted Curve Number ........................ 68.29
Time of Concentration (days hh:mm:ss) 0 00:25:11
Page 20
Sweetwater Ranch Project
SSA Input/Output
Subbasin : P20
Input Data
Area(ac)............. _..... „........................... 6.1
Peak Rate Factor .............._.................. .. 484
Weighted Curve Number ........................ 64.25
Rain Gage ID ....... . ....................„........... Rain Gage-100yr
Composite Curve Number
32 Area Soil Curve
Soil/Surface Description (acres) Group Number
0.29 - 89
5.81 - 63
Composite Area & Weighted CN 6.1 64.25
Time of Concentration
Subarea
Subarea
Subarea
Sheet Flow Computations
A
B
C
Manning's Roughness:
0.15
0
0
Flow Length (ft) :
300
0
0
Slope (%) :
7.3
0
0
2 yr, 24 hr Rainfall (in) :
1.22
0
0
Velocity (ft/sec) :
0.22
0
0
Computed Flow Time (min) :
22.77
0
0
Subarea
Subarea
Subarea
Shallow Concentrated Flow Computat A
B
C
Flow Length (ft) :
212
522
0
Slope (%) :
15
11
0
Surface Type :
3rass pasturere & untille
Unpaved
Velocity (ft/sec) :
2.71
3.32
0
Computed Flow Time (min) :
1.3
2.62
0
Total TOC (min) ..................13.35
Subbasin Runoff Results
Total Rainfall (in) .............................. 2.58
Total Runoff (in) ................................ 0.31
Peak Runoff (cfs) .............................. 1.6
Weighted Curve Number .................. 64.25
###JI##tf##################### 0 00:13:21
Page 21
Sweetwater Ranch Project
SSA Input/output
Subbasin : UH-3
Input Data
Area(ac).......................................... 37.9
Peak Rate Factor ............................. 484
Weighted Curve Number .................. 71.23
Rain Gage ID ........................:.......... Rain Gage-100yr
Composite Curve Number
32
Soil/Surface Description
Area
(acres)
Soil
Group
Curve
Number
Gravel roads
0.3
C
89
Pinyon & Juniper range, Fair
30.4
C
73
Sagebrush range, Fair
7.2
C
63
Composite Area & Weighted CN
37.9
71.23
Time of Concentration
Subarea
Subarea
Subarea
Sheet Flow Computations
A
B
C
Manning's Roughness:
0.3
0.15
0
Flow Length (ft) :
300
3985
0
Slope (%) :
8.7
11.6
0
2 yr, 24 hr Rainfall (in) :
1.22
1.22
0
Velocity (ft/sec) :
0.14
0.44
0
Computed Flow Time (min)
36.95
149.8
0
Subarea
Subarea
Subarea
Shallow Concentrated Flow Computat
A
B
C
Flow Length (ft) :
1023
0
0
Slope (%) :
15
0
0
Surface Type :
Woodland
Unpaved
Unpaved
Velocity (ft/sec) :
1.94
0
0
Computed Flow Time (min) :
8.79
0
0
Total TOC (min) ..................97.77
Subbasin Runoff Results
Total Rainfall (in) .............................. 2.58
Total Runoff (in) ................................ 0.54
Peak Runoff (cfs) .............................. 6.29
Weighted Curve Number .................. 71.23
######tttt#ttttlltt#tttt#tt#tt#tt#tt#### 0 01:37:46
Page 22
Sweetwater Ranch Project
SSA InputlOutput
Subbasin : UH-5
Input Data
Area (ac) ............................
Peak Rate Factor ................
Weighted Curve Number....
Rain Gage ID .....................
Composite Curve Number
Soil/Surface Description
< 50% grass cover, Poor
Gravel roads
Composite Area & Weighted CN
Time of Concentration
...... 2.27
...... 484
86.3
...... Rain Gage-100yr
32 Area Soil
Curve
(acres) Group
Number
1.84 C
86
0.2 C
89
2.04
86.3
User -Defined TOC override (minutes): 10.00
Subbasin Runoff Results
Total Rainfall (in) .............................. 2.58
Total Runoff (in) ................................ 1.33
Peak Runoff (cfs) .............................. 4.19
Weighted Curve Number .................. 86.3
#####►f#p#tttf################t7 0 00:10:00
Page 23
Sweetwater Ranch Project
SSA Input/Output
Subbasin : UH-6
Input Data
Area(ac)..........................................
1.9
Peak Rate Factor .............................
484
Weighted Curve Number ..................
86.32
Rain Gage ID ...................................
Rain Gage-100yr
Composite Curve Number
32
Area Soil
Curve
Soil/Surface Description
Log"Group
Number
< 5m',, grass cover, Poor
1.7 C
86
Gravel roads
0.2 C
89
Composite Area & Weighted CN
1.9
86.32
Time of Concentration
User -Defined TOC override (minutes): 10
Subbasin Runoff Results
Total Rainfall (in) .............................. 2.58
Total Runoff (in) ................................ 1.33
Peak Runoff (cls) .............................. 3.51
Weighted Curve Number .................. 86.32
#### #######*############## 0 00:10:00
Page 24
Culvert Report
Hydraflow Express Extension for Autodesk® Civil 3DO by Autodesk, Inc
CULVERT G1
Invert Elev Dn (ft)
= 7512.10
Pipe Length (ft)
= 76.40
Slope. (%)
= 18.19
Invert Elev Up (ft)
= 7526.00
Rise (in)
= 24.0
Shape
= Circular
Span (in)
= 24.0
No. Barrels
= 1
n-Value
= 0.012
Culvert Type
= Circular Concrete
Culvert Entrance
= Square edge w/headwall (C)
Coeff. K,M,c,Y,k
= 0.0098, 2, 0.0398, 0.67, 0.5
Embankment
Top Elevation (ft)
= 7532.75
Top Width (ft)
= 20.00
Crest Width (ft)
= 20.00
Q&VaffG1
Tuesday, Apr 14 2026
Calculations
Qmin (cfs)
= 36.00
Qmax (cfs)
= 38.00
Tailwater Elev (ft)
= (dc+D)/2
Highlighted
Qtotal (cfs)
= 37.25
Qpipe (cfs)
= 37.25
Qovertop (cfs)
= 0.00
Veloc Dn (ft/s)
= 11.90
Veloc Up (ft/s)
= 11.97
HGL Dn (ft)
= 7514.07
HGL Up (ft)
= 7527.94
Hw Elev (ft)
= 7532.75
Hw/D (ft)
= 3.38
Flow Regime
= Inlet Control
Culvert Report
Hydraflow Express Extension for AutodeskO Civil 3D® by Autodesk, Inc.
Tuesday, Apr 14 2026
CULVERT G2
Invert Elev Dn (ft)
= 7551.38
Calculations
Pipe Length (ft)
= 44.50
Qmin (cfs)
= 16.00
Slope (%)
= 11.17
Qmax (cfs)
= 19.00
Invert Elev Up (ft)
= 7556.35
Tailwater Elev (ft)
= (dc+D)/2
Rise (in)
= 24.0
Shape
= Circular
Highlighted
Span (in)
= 24.0
Qtotal (cfs)
= 18.75
No. Barrels
= 1
Qpipe (cfs)
= 18.75
n-Value
= 0.012
Qovertop (cfs)
= 0.00
Culvert Type
= Circular Concrete
Veloc Dn (ft/s)
= 6.35
Culvert Entrance
= Square edge w/headwall (C)
Veloc Up (ft/s)
= 7.14
Coeff. K,M,c,Y,k
= 0.0098, 2, 0.0398, 0.67, 0.5
HGL Dn (ft)
= 7553.16
HGL Up (ft)
= 7557.91
Embankment
Hw Elev (ft)
= 7559.00
Top Elevation (ft)
= 7559.00
Hw/D (ft)
= 1.32
Top Width (ft)
= 20.00
Flow Regime
= Inlet Control
Crest Width (ft)
= 20.00
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