HomeMy WebLinkAbout12 Drainage ReportGRADING AND DRAINAGE REPORT
O\OLSSON
ASSOCIATES
DRAINAGE REPORT
URSA OPERATING COMPANY, BMC L 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
SGM Project # 2006-479.062
PadL_DrainReport.docx
URSA Operating Company, BMC L March 2017
TABLE OF CONTENTS
1 Introduction 1
1.1 Purpose 1
1.2 Current Site 1
1.3 Methods Used 1
2 Hydraulic and Hydrologic Analysis 1
2.1 Off -Site Drainage 1
2.2 On -Site Drainage 2
2.3 Stormwater Detention 2
3 Hydraulic Analysis 3
4 Stormwater Quality Plan 3
APPENDIX
APPENDIX A - NOAA Atlas 14 Information
APPENDIX B - Rational Method Calculations
ii
URSA Operating Company, BMC L 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 Parcel 1 portion of Battlement Mesa P.U.D.
located between the Battlement Mesa Golf Course and the north end of Spencer Parkway.
The Pad is located below Spencer Parkway. BMC L is served by Spencer Parkway, just
south of the intersection with North Battlement Parkway. The site is sloping from Spencer
Parkway in a northwesterly direction towards the Battlement Mesa Golf Course.
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,
landscape berms and a 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.
2.1 Off -Site Drainage
In its developed condition, BMC L has some introduction of off-site surface drainage from a
smaller 36,000 square foot area (includes landscaped berms) immediately above the access
1
IStorm Return Period 2 year (cfs) 25 year (cfs) 100 year (cfs)
Historic Flow 1.30 3.00 4.50 I
Developed Flow 1.68 3.72 5.65 I
URSA Operating Company, BMC L March 2017
roadway for the pad. Aside from this area, the remaining offsite drainage tributary to the
pad will be routed around the pad. This offsite surface drainage generally exists in the form
of sheet flow from above with no incised tributary channels observed. A small drainage
north of the pad and northern most landscape berm will be slightly rerouted from east to
west to mitigate drainage impacts as a result of berm construction but will be sized and
erosion protected to safely convey flows past the berm and to maintain the historic drainage
pattern around the site.
2.2 On -Site Drainage
The project site in its developed conditions will consist of 2.90 acres of a large gravel pad
and 900 long tributary access road. 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. Two borrow ditches are proposed for the access road
construction to route drainage to a combined detention pond for the increased runoff
detention for the roadway and pad. The developed flows for the site are summarized below.
Table 1 Historic Vs. Developed Flow Rates (Access Road and Pad L Pond)
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 15 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 L
March 2017
Table 2 Stormwater Flow Summary (Pad L Pond)
Pond Location
Runoff
Coefficient
Historic
(Historic)
Runoff
Coefficient
Develo ed
(Developed)
p )
2 -YR Rainfall
Volume, CF
(Historic)Develo
25 -YR Rainfall
Volume, CF
(Historic)
2 -YR Rainfall
Volume, CF
(Developed)
ed
P )
25 -YR Rainfall
Volume, CF
Develo ed
( P )
Pond Storage
Needed for
Detention, CF
(25 -YR)
BMC Pond L
0.5
0.7
1202
2659
1512
3345
686
The maximum calculated detention necessary to capture the stormwater runoff volume
generated from the 25 -year storm is approximately 686 cubic feet for the access road and
for the L Pad combined pond. Detention ponds with this capacity and drainage features to
convey water to the ponds 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. Detention ponds are 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. A similar pond will be constructed for the access road.
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 12" 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
3
URSA Operating Company, BMC L March 2017
activities. Best Management Practices will be utilized during construction to control the
stormwater runoff during construction. Key temporary erosion control measures include
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 L 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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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
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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 L March 2017
APPENDIX B — Rational Method Calculations
6
SIZING CATCH BASIN FOR WELL PAD
Pad Description: URSA PAD L - Developed Conditions
Date: 5/11/2017
Location: URSA Pad L, 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:
Coefficient of Runoff:
Gravel Pad and Road:
Pad and Road Area:
Berms and Trib. area to Pad/Road:
0.8
Tributary berm & undisturbed: 0.5
Rational Method:
Q=CiA
CA Value:
CA Value:
Sum:
343208.00
147,624.00 squ. Ft.
195,584.00 squ. Ft.
Sum:
2.71 Acres
2.24 Acres
Peak Flow (Q, cfs)
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
1.378
2.255
3.048
4.649
15
1.680
2.751
3.717
5.650
30
2.230
3.801
5.006
7.137
60
2.766
4.575
5.848
8.079
Volume of Runoff (cf)
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
826.691
1353.037
1828.830
2789.338
15
1512.131
2475.612
3345.421
5085.041
30
4014.506
6842.502
9010.335
12846.419
60
9955.974
16468.395
21053.853
29082.864
http://hdsc.nws.noaa.gov/hdsc/pfds/pfds map cont.html
4.96 Acres
3.389 Acres
4.490 Acres
7.879 Acres
SIZING CATCH BASIN FOR WELL PAD
Pad Description: URSA PAD L - Historic Conditions
Date: 5/11/2017
Location: URSA Pad L, 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:
147,624.00 squ. Ft.
Trib. area to Pad/Road: 195,584.00 squ. Ft.
0.5
0.5
CA Value:
CA Value:
Sum:
1.69 Acres
2.24 Acres
Peak Flow (Q, cfs)
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
1.095
1.792
2.423
3.695
15
1.335
2.186
2.955
4.491
30
1.773
3.022
3.979
5.673
60
2.198
3.636
4.649
6.421
Volume of Runoff (cf)
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
657.11
1075.48
1453.67
2217.14
15
1201.94
1967.77
2659.15
4041.91
30
3190.98
5438.85
7161.99
10211.15
60
7913.64
13090.12
16734.94
23116.90
http://hdsc.nws.noaa.gov/hdsc/pfds/pfds map cont.html
Worksheet: Pond L Outlet
Solve fer:IDischarge
Man ing's Formula 4
Mannings Coefficient:I0.012 J
Channel Slope: DEI1M-E It/0
Depth;11H1 ft
Diameter:12.0 in
Discharge: (3.05
cfs
Flow Areal o.4 ft.
Wetted Perimeter.1 1.57 ft
Top Width: 0.06
Critical Depth:1 0.75 R
Percent Full: 50.0
Critical Slope' 0.007543 fVrt
Velocity: 7.77 ft/s
Velocity Head: 0.94 ft
Specific Energy_ 1 44 ft
Froude Number: 2.19
Maximum Discharge: 6.5S cfs
Discharge Full: 610 cfs
Slope Full:, T006250 R/0
Flow Typed Supercritical
1 $oIne
Hepod Close Help
3.94 Acres
3.389 Acres
4.490 Acres
Detention Volume Required (CF)
Recurrence Interval (Years)
Duration (minutes)
2
10
25
100
10
170
278
375
572
15
310
508
686
1043
30
824
1404
1848
2635
60
2042
3378
4319
5966
For pond sizing:
Detained
Contour Area Volume Cumm. Volume Comment
5420 565
5421.5 1922 1244 1876
5423 2526 2224 3468
DESIGN OVERFLOW CULVERT FOR 4.5 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
4000
3500
3000
2500
2000
1500
1000
500
0
5420
Volume established at
5073.4 contour
Depth in pond:
0.49 feet