HomeMy WebLinkAbout12 Grading_Drainage RptGRADING AND DRAINAGE REPORT
O\OLSSON
ASSOCIATES
DRAINAGE REPORT
URSA OPERATING COMPANY, BMC A PAD
March, 2017
PREPARED BY
6SGM
I 18 WEST SIXTH STREET, SUITE 200
GLENWOOD SPRINGS, CO 81601
970.945.1 004
970.945.5948 FAX
URSA Operating Company, BMC A March 2017
TABLE OF CONTENTS
SGM Project # 2006-479.062
PadA_DrainReport.docx
1 Introduction 1
1.1 Purpose 1
1.2 Current Site 1
1.3 Methods Used
2 Hydraulic and Hydrologic Analysis
2.1 Off -Site Drainage
2.2 On -Site Drainage
2.3 Stormwater Detention
3 Hydraulic Analysis
4 Stormwater Quality Plan
APPENDIX
APPENDIX A - NOAA Atlas 14 Information
APPENDIX B - Rational Method Calculations
1
1
2
2
2
3
3
ii
URSA Operating Company, BMC A March 2017
1 Introduction
1.1 Purpose
The purpose of this drainage report is to provide calculations for storm water runoff volumes
to be detained on-site. This report contains a discussion of both off-site and on-site
drainage and the methodology used to design various drainage elements. The designed
drainage elements ensure that storm water runoff produced from the 24 hour storm will be
detained and treated on site to reduce possible contamination off-site.
1.2 Current Site
The project site is currently a vacant lot in the Unplatted portion of Battlement Mesa P.U.D.
located between the Tamarisk/Monument Creek Village Subdivisions and the Battlement
Mesa Metropolitan District's Wastewater Treatment Facility. The Pad is located below the
bluff that both Tamarisk and Monument Creek Village Subdivisions sit on. BMC A is served
by River Bluff Road, south of Interstate 70 and the Colorado River. The site is relatively flat
riverfront land sloping toward the Colorado River. There is grading and soil wall nailing
proposed to minimize visual impacts that would be otherwise visible from Parachute and the
Interstate 70 corridor.
The project site, in its pre -developed condition, is located in a semiarid plateau region
between 5000 ft. and 6000 ft. in elevation. The vegetative cover consists of mostly sage
brush and juniper mix. A majority of the drainage basin for the project is composed of
hydraulic soil group C and D.
1.3 Methods Used
The Rational Method was used to produce a conservative set of hydrologic flood peak
calculations for sizing particular drainage elements (i.e., the Rational Method would predict
higher flood peaks than alternative methods). The Rational Method uses the equation
below:
Q = CiA Equation 1
where:
Q = flow rate (cfs)
C = runoff coefficient based on soil type and cover
i = rainfall intensity corresponding to the time of concentration
A = basin area (acres).
2 Hydraulic and Hydrologic Analysis
The project site in its developed condition will consist of a main gravel entrance road and
large gravel pad. Because only a small portion of the site is being developed, only these
areas will be analyzed in the detention calculations due to the rest of the site maintaining
historic flow patterns and characteristics. Drainage facilities will be provided to route
tributary/offsite flows around the pad into the common historic flow paths associated with the
property containing this pad.
1
IStorm Return Period 2 year (cfs) 25 year (cfs) 100 year (cfs) I
Historic Flow 1.56 3.30 4.56 I
Developed Flow 1.96 4.09 5.65 I
URSA Operating Company, BMC A March 2017
2.1 Off -Site Drainage
In its developed condition, BMC A has some introduction of off-site surface drainage from
other properties above the pad. This offsite surface drainage generally exists in the form of
sheet flow from above with no incised tributary channels observed. An utility access corridor
exists above and east of the site between Tamarisk Subdivision that serves to route
drainage from the subdivision to the east of the project site. For the sheet flow area
immediately above the site, the tributary off-site drainage shall be redirected by constructing
a valley pan at the base of the proposed soil nail wall and redirecting the offsite drainage
around the pad (prior to entering directly onto the pad). For the road area of the pad, a
borrow ditch will collect the tributary offsite flow and transfer it around the pad area into the
historic drainage path for the site.
2.2 On -Site Drainage
The project site in its developed conditions will consist of 5.59 acres of a large gravel pad
and tributary access road area. Compared to historic conditions, construction of the
proposed developed conditions would produce a reduction in pervious ground cover,
resulting in a minor change to the runoff coefficient. This will result in an increase in peak
discharge of the 24 hour storm and detention will be needed for the stormwater flowing
across the developed site. The developed flows for the site are summarized below.
Table 1 Historic Vs. Developed Flow Rates
The flows shown above are determined from a rainfall intensity corresponding to the 24 hour
storm and appropriate storm return period. These intensities and the flow calculations can
be seen in the appendix. Note that the time of concentration (or storm duration) used in the
analysis is 60 minutes.
2.3 Stormwater Detention
For the purpose of this report and this project, it will be required to detain the additional
stormwater runoff volume generated from the developed site from historic conditions. In order
to determine required detention, the developed and historic stormwater runoff volumes were
analyzed. Storm runoff volume was calculated from the 2 and 25 year, 24 hour storm
precipitation depth determined from the NOAA Atlas 14 information. These depths for each
storm return period can be seen in the appendix. The runoff volume of the site was calculated
from area of the developed site multiplied by the 2 and 25 year, 24 hour precipitation depth
and the weighted runoff coefficient for the appropriate site condition.
2
URSA Operating Company, BMC A
March 2017
Table 2 Stormwater Flow Summary
Pond Location
Runoff
Coefficient
HistoricHistoric
(Historic)
Runoff
Coefficient
(Developed)
2 -YR Rainfall
Volume, CF
( )
25 -YR Rainfall
Volume, CF
Historic
( )
2 -YR Rainfall
Volume, CF
Develo ed
( P )
25 -YR Rainfall
Volume, CF
(Developed)
Pond Storage
Needed for
Detention, CF
(25 -YR)
BMC Pond A
0.5
0.7
5618
11881
6969
14736
2855
The maximum calculated detention necessary to capture the stormwater runoff volume
generated from the 25 -year storm is approximately 2,855 cubic feet. A detention pond with
this capacity and drainage features to convey water to the pond will be provided on site.
Pond specific size calculations are attached in the appendix of this report.
3 Hydraulic Analysis
The site design will require various drainage features including ditches and culverts. These
will be required to divert the storm water runoff away from the site appropriately.
4 Stormwater Quality Plan
The main goal of the site design is to provide detention for the project, and ensure the post -
development peak discharge rates do not exceed the pre -development peak flow rates.
The only area where a significant increase in runoff coefficients occur is the gravel pad and
road. A detention pond will be sized appropriately and provide a location for sedimentation
of the storm water runoff generated from the developed site. The remaining site will remain
native vegetation and provide historic flow patterns and characteristics.
There is an increase of runoff generated with the construction the gravel pad and associated
access road. This increase in runoff is measurable, however; a detention pond will be
constructed just downstream of the respective pad, with a controllable outfall pipe and valve
structure. The controlling valves in the detention pond discharge pipes will each be left in
the normally open position at approximately 60% open. Alternatively, these valves can be
closed in the event of a non-compliant release, and further ensure no detrimental impact to
the surrounding area.
In order to minimize any threat of property damage, the respective pond structures will have
an 18" culvert pipe installed at a higher elevation, along with the normal use 8" discharge
pipe, in order to facilitate conveying the 100 year storm event safely to the respective outfall
drainage features. Both proposed detention ponds will discharge into existing "natural
channel" drainage features. It is not anticipated for any additional erosion and
sedimentation protection beyond that proposed at the pipe outfalls. The operator will
monitor outfall locations to ensure there is no channel scour or additional erosion cause by
the detention pond outfall pipe. Supporting calculations have been included in the appendix
of this report.
Temporary erosion control measures will be required for the duration of construction. A
CDPHE Stormwater Permit for Construction activities will be obtained prior to construction
activities. Best Management Practices will be utilized during construction to control the
stormwater runoff during construction. Key temporary erosion control measures include
3
URSA Operating Company, BMC A March 2017
installation and maintenance of straw wattles, inlet protection, a stabilized construction
entrance and all necessary acceptable best management practices that would relate to this
project. See Ursa's Stormwater Management Plan (SWMP) for more details.
4
URSA Operating Company, BMC A March 2017
APPENDIX A —NOAA Atlas 14 Information
Appendix
5
Precipitation Frequency Data Server
Page 1 of 3
NOAA Atlas 14, Volume 8, Version 2
Location name: Parachute, Colorado, US*
Latitude: 39.4472°, Longitude: -108.0330°
Elevation: 5202 ft*
source: Google Maps
POINT PRECIPITATION FREQUENCY ESTIMATES
Sanja Perica, Deborah Martin, Sandra Pavlovic, Ishani Roy, Michael St. Laurent, Carl Trypaluk, Dale
Unruh, Michael Yekta, Geoffery Bonnin
NOAA, National Weather Service, Silver Spring, Maryland
PF tabular 1 PF graphical 1 Maps & aerials
PF tabular
PDS -based point precipitation frequency estimates with 90% confidence intervals (in inches)1
Average recurrence interval (years)
Duration
1
2
5
10
25
50
100
200
500
1000
5 -min
0.137
(0.110-0.173)
0.162
(0.130-0.205)
0.215
(0.172-0.273)
0.269
(0.215-0.344)
0.360
(0.284-0.500)
0.443
(0.336-0.618)
0.536
(0.391-0.769)
0.643
(0.446-0.948)
0.800
(0.531-1.22)
0.933
(0.595-1.42)
10 -min
0.200
(0.161-0.253)
0.237
(0.191-0.300)
0.314
(0.252-0.400)
0.394
(0.314-0.504)
0.527
(0.416-0.732)
0.648
(0.492-0.905)
0.785
(0.572-1.13)
0.941
(0.653-1.39)
1.17
(0.777-1.78)
1.37
(0.871-2.07)
15 -min
0.244
(0.197-0.309)
0.289
(0.233-0.366)
0.383
(0.308-0.487)
0.481
(0.383-0.614)
0.643
(0.507-0.893)
0.791
(0.600-1.10)
0.958
(0.698-1.37)
1.15
(0.797-1.69)
1.43
(0.948-2.17)
1.67
(1.06-2.53)
30 -min
0.309
(0.249-0.390)
0.389
(0.313-0.492)
0.534
(0.428-0.678)
0.667
(0.532-0.853)
0.872
(0.677-1.19)
1.05
(0.786-1.44)
1.23
(0.891-1.74)
1.44
(0.990-2.10)
1.73
(1.14-2.60)
1.96
(1.25-2.98)
60 -min
0.389
(0.313-0.492)
0.484
(0.390-0.613)
0.652
(0.523-0.828)
0.802
(0.639-1.03)
1.03
(0.792-1.38)
1.21
(0.908-1.66)
1.41
(1.01-1.98)
1.62
(1.11-2.35)
1.91
(1.26-2.87)
2.15
(1.37-3.26)
2 -hr
0.469
(0.382-0.586)
0.580
(0.472-0.725)
0.770
(0.624-0.966)
0.936
(0.754-1.18)
1.18
(0.917-1.56)
1.37
(1.04-1.85)
1.58
(1.15-2.18)
1.80
(1.25-2.57)
2.10
(1.40-3.09)
2.33
(1.51-3.49)
3 -hr
0.536
(0.439-0.665)
0.641
(0.525-0.796)
0.824
(0.672-1.03)
0.985
(0.798-1.23)
1.22
(0.959-1.61)
1.42
(1.08-1.89)
1.62
(1.19-2.22)
1.84
(1.29-2.60)
2.14
(1.44-3.13)
2.38
(1.55-3.53)
6 -hr
0.661
(0.548-0.809)
0.773
(0.639-0.947)
0.963
(0.794-1.18)
1.13
(0.924-1.39)
1.37
(1.08-1.77)
1.56
(1.20-2.05)
1.76
(1.31-2.38)
1.97
(1.40-2.75)
2.26
(1.54-3.25)
2.49
(1.64-3.64)
12 -hr
0.819
(0.685-0.989)
0.946
(0.791-1.14)
1.16
(0.967-1.41)
1.35
(1.12-1.64)
1.61
(1.29-2.05)
1.83
(1.43-2.36)
2.05
(1.54-2.73)
2.28
(1.64-3.13)
2.61
(1.79-3.69)
2.86
(1.91-4.11)
24 -hr
0.993
(0.840-1.18)
1.14
(0.964-1.36)
1.39
(1.17-1.67)
1.61
(1.35-1.94)
1.92
(1.56-2.41)
2.17
(1.71-2.76)
2.43
(1.85-3.18)
2.70
(1.97-3.65)
3.07
(2.15-4.29)
3.37
(2.28-4.77)
2 -day
1.17
(1.00-1.38)
1.35
(1.15-1.58)
1.64
(1.40-1.94)
1.90
(1.60-2.25)
2.26
(1.85-2.78)
2.55
(2.03-3.19)
2.84
(2.19-3.67)
3.16
(2.33-4.20)
3.58
(2.53-4.91)
3.92
(2.69-5.46)
3 -day
1.29
(1.11-1.50)
1.48
(1.27-1.73)
1.81
(1.55-2.12)
2.09
(1.78-2.46)
2.49
(2.05-3.04)
2.81
(2.26-3.49)
3.13
(2.43-4.00)
3.48
(2.58-4.58)
3.94
(2.81-5.36)
4.31
(2.99-5.95)
4 -day
1.39
(1.20-1.61)
1.59
(1.38-1.85)
1.94
(1.67-2.26)
2.24
(1.92-2.62)
2.67
(2.21-3.24)
3.01
(2.43-3.71)
3.36
(2.62-4.26)
3.72
(2.78-4.87)
4.22
(3.02-5.69)
4.60
(3.21-6.31)
7 -day
1.63
(1.42-1.87)
1.87
(1.62-2.14)
2.26
(1.96-2.60)
2.60
(2.24-3.00)
3.07
(2.56-3.68)
3.44
(2.80-4.19)
3.82
(3.01-4.78)
4.22
(3.18-5.44)
4.75
(3.44-6.32)
5.16
(3.64-6.99)
10 -day
1.85
(1.62-2.10)
2.10
(1.84-2.39)
2.52
(2.20-2.87)
2.87
(2.49-3.29)
3.37
(2.83-4.00)
3.76
(3.08-4.54)
4.16
(3.29-5.15)
4.56
(3.46-5.84)
5.11
(3.73-6.74)
5.54
(3.93-7.43)
20 -day
2.47
(2.19-2.77)
2.76
(2.45-3.10)
3.24
(2.86-3.64)
3.64
(3.19-4.11)
4.19
(3.55-4.89)
4.61
(3.83-5.47)
5.04
(4.04-6.14)
5.48
(4.21-6.88)
6.06
(4.48-7.84)
6.50
(4.68-8.57)
30 -day
2.99
(2.67-3.32)
3.33
(2.97-3.71)
3.89
(3.45-4.33)
4.34
(3.84-4.87)
4.96
(4.24-5.73)
5.43
(4.54-6.38)
5.90
(4.76-7.11)
6.37
(4.94-7.91)
6.98
(5.21-8.94)
7.44
(5.41-9.72)
45 -day
3.64
(3.27-4.01)
4.07
(3.66-4.49)
4.77
(4.27-5.27)
5.33
(4.74-5.92)
6.08
(5.22-6.93)
6.64
(5.57-7.70)
7.17
(5.83-8.55)
7.70
(6.01-9.46)
8.38
(6.29-10.6)
8.86
(6.50-11.5)
60 -day
4.18
(3.77-4.58)
4.72
(4.26-5.17)
5.57
(5.01-6.12)
6.25
(5.59-6.90)
7.13
56.14-8.07)
7.78
(6.56-8.95)
8.40
(6.85-9.92)
8.99
(7.05-10.9)
9.73
(7.34-12.2)
10.2
(7.57-13.2)
1 Precipitation frequency (PF) estimates in this table are based on frequency analysis o partial duration series (PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a
given dura ion 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 PMP values.
Please refer to NOAA Atlas 14 document for more information.
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PF graphical
http://hdsc.nws.noaa.gov/hdsc/pfds/pfds printpage.html?lat=39.4472&lon=-108.0330&dat... 9/30/2014
Precipitation Frequency Data Server
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Page 2 of 3
Average recurrence
interval
{years}
— 1
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— 5
— 10
— 25
— 50
— 100
— 200
— 500
— 1000
Duration
— 5 -min — 2 -day
— 10 -min — 3 -day
15 -min --- 4 -day
— 30 -min — 7 -day
— 60 -min — 10 -day
— 24r — 20 -day
— 3 -he — 30 -day
— 6 -Sr — 45 -day
— 12 -hr — 60 -day
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Precipitation Frequency Data Server Page 3 of 3
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US Department of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
Office of Hydrologic Development
1325 East West Highway
Silver Spring, MD 20910
Questions?: HDSC.Questions(&noaa.gov
Disclaimer
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Precipitation Frequency Data Server
Page 1 of 3
NOAA Atlas 14, Volume 8, Version 2
Location name: Parachute, Colorado, US*
Latitude: 39.4472°, Longitude: -108.0330°
Elevation: 5202 ft*
source: Google Maps
POINT PRECIPITATION FREQUENCY ESTIMATES
Sanja Perica, Deborah Martin, Sandra Pavlovic, Ishani Roy, Michael St. Laurent, Carl Trypaluk, Dale
Unruh, Michael Yekta, Geoffery Bonnin
NOAA, National Weather Service, Silver Spring, Maryland
PF tabular 1 PF graphical 1 Maps & aerials
PF tabular
PDS -based point precipitation frequency estimates with 90% confidence intervals in inches/hour)1
Average recurrence interval (years)
Duration
1
2
5
10
25
50
100
200
500
1000
5 -min
1.64
(1.32-2.08)
1.94
(1.56-2.46)
2.58
(2.06-3.28)
3.23
(2.58-4.13)
4.32
(3.41-6.00)
5.32
(4.03-7.42)
6.43
(4.69-9.23)
7.72
(5.35-11.4L
9.60
(6.37-14.6)
11.2
(7.14-17.0)
10 -min
1.20
(0.966-1.52)
1.42
(1.15-1.80)
1.88
(1.51-2.40)
2.36
(1.88-3.02)
3.16
(2.50-4.39)
3.89
(2.95-5.43)
4.71
(3.43-6.76)
5.65
(3.92-8.33)
7.03
(4.66-10.7)
8.20
(5.23-12.4)
15 -min
0.976
(0.788-1.24)
1.16
(0.932-1.46)
1.53
(1.23-1.95)
1.92
(1.53-2.46)
2.57
(2.03-3.57)
3.16
(2.40-4.42)
3.83
(2.79-5.49)
4.59
(3.19-6.77)
5.72
(3.79-8.68)
6.66
(4.25-10.1)
30 -min
0.618
(0.498-0.780)
0.778
(0.626-0.984)
1.07
(0.856-1.36)
1.33
(1.06-1.71)
1.74
(1.35-2.37)
2.09
(1.57-2.88)
2.46
(1.78-3.49)
2.87
(1.98-4.19)
3.45
(2.28-5.20)
3.93
(2.50-5.96)
60 -min
0.389
(0.313-0.492)
0.484
(0.390-0.613)
0.652
(0.523-0.828)
0.802
(0.639-1.03)
1.03
(0.792-1.38)
1.21
(0.908-1.66)
1.41
(1.01-1.98)
1.62
(1.11-2.35)
1.91
(1.26-2.87)
2.15
(1.37-3.26)
2 -hr
0.234
(0.191-0.293)
0.290
(0.236-0.362)
0.385
(0.312-0.483)
0.468
(0.377-0.590)
0.589
(0.458-0.780)
0.687
(0.520-0.924)
0.789
(0.575-1.09)
0.898
(0.624-1.28)
1.05
(0.698-1.55)
1.17
(0.753-1.74)
3 -hr
0.178
(0.146-0.221)
0.213
(0.175-0.265)
0.274
(0.224-0.342)
0.328
(0.266-0.411)
0.407
(0.319-0.535)
0.471
(0.360-0.629)
0.539
(0.396-0.740)
0.611
(0.429-0.867)
0.712
(0.478-1.04)
0.792
(0.516-1.18)
6 -hr
0.110
0.129
0.161
0.189
0.228
0.261
0.294
0.329
0.377
0.416
(0.092-0.135)
(0.107-0.158)
(0.133-0.198)
(0.154-0.233)
(0.181-0.295)
(0.201-0.342)
(0.218-0.397)
(0.233-0.458)
(0.257-0.543)
(0.274-0.607)
12 -hr
0.068
(0.057-0.082)
0.079
(0.066-0.095)
0.096
(0.080-0.117)
0.112
(0.093-0.136)
0.134
(0.107-0.170)
0.152
(0.118-0.196)
0.170
(0.128-0.226)
0.190
(0.136-0.260)
0.216
(0.149-0.306)
0.237
(0.159-0.341)
24 -hr
0.041
(0.035-0.049)
0.048
(0.040-0.057)
0.058
(0.049-0.069)
0.067
(0.056-0.081)
0.080
(0.065-0.100)
0.091
(0.071-0.115)
0.101
(0.077-0.133)
0.113
(0.082-0.152)
0.128
(0.089-0.179)
0.140
(0.095-0.199)
2 -day
0.024
(0.021-0.029)
0.028
(0.024-0.033)
0.034
(0.029-0.040)
0.039
(0.033-0.047)
0.047
(0.038-0.058)
0.053
(0.042-0.066)
0.059
(0.046-0.076)
0.066
(0.048-0.087)
0.075
(0.053-0.102)
0.082
(0.056-0.114)
3 -day
0.018
(0.015-0.021)
0.021
(0.018-0.024)
0.025
(0.022-0.029)
0.029
(0.025-0.034)
0.035
(0.028-0.042)
0.039
(0.031-0.048)
0.044
(0.034-0.056)
0.048
(0.036-0.064)
0.055
(0.039-0.074)
0.060
(0.041-0.083)
0.014
0.017
0.020
0.023
0.028
0.031
0.035
0.039
0.044
0.048
4 -day
(0.012-0.017)
(0.014-0.019)
(0.017-0.024)
(0.020-0.027)
(0.023-0.034)
(0.025-0.039)
(0.027-0.044)
(0.029-0.051)
(0.031-0.059)
(0.033-0.066)
7 -day
0.010
(0.008-0.011)
0.011
(0.010-0.013)
0.013
(0.012-0.015)
0.015
(0.013-0.018)
0.018
(0.015-0.022)
0.020
(0.017-0.025)
0.023
(0.018-0.028)
0.025
(0.019-0.032)
0.028
(0.020-0.038)
0.031
(0.022-0.042)
10 -day
0.008
(0.007-0.009)
0.009
(0.008-0.010)
0.010
(0.009-0.012)
0.012
(0.010-0.0141
0.014
(0.012-0.017)
0.016
(0.013-0.0191
0.017
(0.014-0.021)
0.019
(0.014-0.024)
0.021
(0.016-0.028)
0.023
(0.016-0.031)
20 -day
0.005
(0.005-0.006)
0.006
(0.005-0.006)
0.007
(0.006-0.008)
0.008
(0.007-0.009)
0.009
(0.007-0.010)
0.010
(0.008-0.011)
0.011
(0.008-0.013)
0.011
(0.009-0.014)
0.013
(0.009-0.016)
0.014
(0.010-0.018)
30 -day
0.004
(0.004-0.005)
0.005
(0.004-0.005)
0.005
(0.005-0.006)
0.006
(0.005-0.007)
0.007
(0.006-0.008)
0.008
(0.006-0.009)
0.008
(0.007-0.010)
0.009
(0.007-0.011)
0.010
(0.007-0.012)
0.010
(0.008-0.013)
45 -day
0.003
(0.003-0.004)
0.004
(0.003-0.004)
0.004
(0.004-0.005)
0.005
(0.004-0.005)
0.006
(0.005-0.006)
0.006
(0.005-0.007)
0.007
(0.005-0.008)
0.007
(0.006-0.009)
0.008
(0.006-0.010)
0.008
(0.006-0.011)
60 -day
0.003
(0.003-0.003)
0.003
(0.003-0.004)
0.004
(0.003-0.004
0.004
(0.004-0.005)
0.005
(0.004-0.006)
0.005
(0.005-0.006)
0.006
(0.005-0.007)
0.006
(0.005-0.008)
0.007
(0.005-0.008)
0.007
(0.005-0.009)
1 Precipitation frequency (PF) estimates in this table are based on frequency analysis o partial duration series (PDS).
Numbers 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 upper bounds are not
checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
Back to Top
PF graphical
http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=39.4472&lon=-108.03 30&dat... 9/30/2014
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Duration
— 5 -min — 2 -day
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— 30 -min — 7 -day
— 60 -min — 10 -day
— 2 -hr — 20 -day
— 3 -hr — 30 -Clay
— 6 -hr — 45 -day
— 12 -hr — 60 -day
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US Department of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
Office of Hydrologic Development
1325 East West Highway
Silver Spring, MD 20910
Questions?: HDSC.Questions(&noaa.gov
Disclaimer
http://hdsc.nws.noaa.gov/hdsc/pfds/pfds printpage.html?lat=39.4472&lon=-108.0330&dat... 9/30/2014
URSA Operating Company, BMC A March 2017
APPENDIX B — Rational Method Calculations
6
SIZING CATCH BASIN FOR WELL PAD
Pad Description: URSA PAD A - Developed Conditions
Date: 3/21/2017
Location: URSA Pad A, Parachute, Garfield County
Rainfall Intensity Data Table
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
0.278
0.455
0.615
0.938
15
0.339
0.555
0.750
1.140
30
0.450
0.767
1.010
1.440
60
0.558
0.923
1.180
1.630
To populate Data Table, refer to website below.
Area of Pad Calculations:
Coefficienst of Runoff:
Gravel Pad and Road:
Tributary undisturbed:
Rational Method: Q=CiA
Pad and Road Area:
Trib. area to Pad/Road:
0.8
0.5
CA Value:
CA Value:
Sum:
97596.20 squ. Ft.
146065 squ. Ft.
Sum:
1.79 Acres
1.68 Acres
Peak Flow (Q, cfs)
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
0.964
1.578
2.133
3.254
15
1.176
1.925
2.602
3.955
30
1.561
2.661
3.504
4.995
60
1.936
3.202
4.093
5.654
Volume of Runoff (cf)
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
578.629
947.036
1280.059
1952.351
15
1058.391
1732.763
2341.572
3559.190
30
2809.887
4789.296
6306.634
8991.637
60
6968.519
11526.779
14736.294
20356.068
http://hdsc.nws.noaa.gov/hdsc/pfds/pfds map cont.html
3.47 Acres
2.241 Acres
3.353 Acres
5.594 Acres
SIZING CATCH BASIN FOR WELL PAD
Pad Description: URSA PAD A - Historic Conditions
Date: 5/12/2017
Location: URSA Pad A, Parachute, Garfield County
Rainfall Intensity Data Table
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
0.278
0.455
0.615
0.938
15
0.339
0.555
0.750
1.140
30
0.450
0.767
1.010
1.440
60
0.558
0.923
1.180
1.630
To populate Data Table, refer to website below.
Area of Pad Calculations:
Coefficienst of Runoff:
Gravel Pad and Road:
Tributary undisturbed:
Rational Method: Q=CiA
Pad and Road Area:
Trib. area to Pad/Road:
0.5
0.5
CA Value:
CA Value:
Sum:
97596.20 squ. Ft.
146065 squ. Ft.
1.12 Acres
1.68 Acres
Peak Flow (Q, cfs)
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
0.778
1.273
1.720
2.623
15
0.948
1.552
2.098
3.188
30
1.259
2.145
2.825
4.027
60
1.561
2.581
3.300
4.559
Volume of Runoff (cf)
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
466.51
763.54
1032.04
1574.06
15
853.32
1397.02
1887.87
2869.56
30
2265.45
3861.33
5084.67
7249.42
60
5618.30
9293.36
11881.00
16411.89
http://hdsc.nws.noaa.gov/hdsc/pfds/pfds map cont.html
Iffl Worksheet: Pad A Pond Outlet
Solve fa: ID'rtcharpe J Manig's Formula 10
Mannings Coefficient:I0.028 _I
Channel Slope:10.004060 f1/It
Depth: 1.40 11
Diameter: 191 h
Discharge:13.32 cfs
lSolve
Flom Areal 1.7 IF
Welled Pernnelec[ 3.93 ft
Top Width[ on
Critical Depth:[ 0.69 ft
Percent Fut 93-3 %6
Critical Slope: 024167 ft111
Velocity:1 1.93 ftla
Velocity Head 0.06 ft
Specific Energy: 1-1.46 ft
Fronde Numbes:1 0.22
Maxamum Discharge:{ 3.32 Gs
Discharge Full: 3.08 ds
Slope Frit) 0.0 4627 ft/ft
Flow Typo) 46cn1'cal
Deport I Close 1 Help
2.80 Acres
2.241 Acres
3.353 Acres
5.594
Detention Volume Required (CF)
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
112
183
248
378
15
205
336
454
690
30
544
928
1222
1742
60
2233
2855
3944
For pond sizing:
Detained
Contour Area Cumm. Volume Comment
Volume
5069 335
5070 1158 747 747
5071 1508 1333 2080
5072 1722 1615 3695
5073 2030 1876 5571
5074 2526 2278 7849
DESIGN OVERFLOW CULVERT FOR 5.7 CFS
DRAIN CULVERT CAN BE AN 12" PIPE WITH A HEADGATE ON IT.
NORMAL MAINTENANCE WOULD ALLOW DRAINING OF THE POND
IN NON PRECIPITATION EVENTS AND COLLECTION OF SEDIMENT TO
MAINTAIN THE 25 YEAR VOLUME OF RUNOFF FROM PAD AND ROAD
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
Stage/Storage
----------
t�t�tttta>_1-i
_ I
WSW-
--'-
111111111.1."'-
5069
5070
5071
5072
5073
5074
• Volume
Volume established at
5071.4 contour
Depth in pond:
2.4 feet