HomeMy WebLinkAboutFDP201900004 Calculations Floodplain Development Permit 2019-05-10 Peak Discharges Using Anderson Method
18160- Oakencroft
5/10/19
Results of calculations below
Maximum rate of runoff(cfs)
10 yr 25 yr 100 yr
Reach 1= 942 1405 2323
Anderson Method Variables
Road Length= 61,646 ft
Road Area Estimate*= 1,232,922 ft2
*Estimate 20ft for average width of roadways
Forested Area on USGS map= 26,125,060 ft2
Developed Area on USGS map=. 73,460,228 ft2
1,686 ac
Estimated houses on site**. 337
**Estimate 1 house per 5 acres of developed land
Total area of home footprint*** 505,924 ft2
***Estimated average home footprint of 1,500 sq feet
Driveway area****= 337,283 ft2
****Estimate driveways as(20ftx50ft)per house
Estimated impervious area within watershed= 2,076,129 ft2
Total watershed area= 99,585,288 ft2
Percent impervious within watershed= 2.08 %
Estimate of growth= 1.01
Approximate percentage of impervious area (I)= 2.10
Coefficient of imperviousness (K)
K= 1 +0.015I
K= 1.0315
Drainage area (A)
A= 3.57 mi2
Length along primary watercourse from site to watershed boundary(L)
L= 2.11 mi
10% L= 0.21 mi 1,112 ft
85%L= 1.79 mi 9,448 ft
Elevation at 10%L= 446
Elevation at 85% L= 560
Index of basin slope based on slope between points 10%and 85%of L(S)
S= 87.47 ft/mi
Woolley Engineering Page 1 of 2 Exhibit E
Peak Discharges Using Anderson Method
18160- Oakencroft
5/10/19
Time lag-developed watersheds partially channelized
T=4.64( )0.42
T= 2.48 Hrs.
Flood Frequency Ratio*for flood frequency"f'
f 10 25 100
Rn 2.2 3.3 5.5
R100 1.45 1.8 2.2
*VDOT Drainage Manual-Chapter 6
Where:
RN =Flood frequency ratio for 0%impervious(completely rural)for flood frequency"f"
Rive =Flood frequency ratio for 100%imperviousness for flood frequency"f
_RN+0.011(2.5R100—RN)
Rf 1.00+0.0151
R10= 2.16
R25= 3.22
R100= 5.33
Maximum rate of runoff for flood frequency"f" (Q)
Qf = Rf(230)KA0.82T-0.48
Q10= 942.00 cfs
Q25= 1,404.68 cfs
Q100= 2,323.39 cfs
Woolley Engineering Page 2 of 2 Exhibit E
.
RECEIVED
MAY 1 3 7019
COMMUNITY
DEVELOPMENT
11/28/2018 StreamStats
X-SEC 3 FLOW DATA
Region ID: VA
Workspace ID: VA201 81 1 281 929231 61 000
Clicked Point (Latitude, Longitude): 38.08188, -78.55203
Time: 201 8-1 1-28 14:29:40 -0500
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Basin Characteristics
Parameter Code Parameter Description Value Unit
DRNAREA Area that drains to a point on a stream 3.39 square miles
Peak-Flow Statistics Parameters[Blue Ridge 2011 5144)
Parameter Code Parameter Name Value Units Min Limit Max Limit
DRNAREA Drainage Area 3.39 square miles 0.06 7866
Peak-Flow Statistics Flow Report iIe Ridge 2011 5144]
https://streamstats.usgs.gov/ss/ 1/2
•
11128/2018 StreamStets
PII: Prediction Interval-Lower, Plu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE:
Standard Error (other-- see report)
Statistic Value Unit SEp
2 Year Peak Flood 318 ft^3/s 17
•
2 33 Year Peak Flood 376 .ft"3/s 18
5 Year Peak.Flood 699 ft"3/s ' 20 •
10 Year Peak Flood 1080 ft"3/s 24
25 Year Peak Flood • 1680 . ft^3/s 29
•
50 Year Peak Flood 2270 ft"3/s 32
100 Year Peak Flood 3150 ft^3/s• 30
200 Year Peak Flood • • • 3970 ft^3/s 33
•
Peak-Row Statistics Citations
Austin, S.H., Krstolic,_J.L., and Wiegand, Ute,2011, Peak-flow characteristics of Virginia
streams: U.S. Geological.Survey Scientific Investigations Report 2011-5144, 106 p. + 3
tables and 2.appendixes on CD. (http://pubs.usgs.gov/sir/2011/51441)
•
USGS Data Disclaimer:Unless otherwise stated,all data,metadata and related materials are considered
to satisfy the quality standards relative to the purpose for Which the data were collected:Although these
data and associated metadata have been reviewed for accuracy and completeness and approved for
release by the U.S.Geological Survey(USGS),no warranty expressed or implied is made regarding the•
display or utility of the data for other purposes,nor on all computer systems,nor shall the act of
distribution constitute any such warranty. . .. •
. USGS Software Disclaimer:This software has been approved for release by the U.S.Geological'Survey
(USGS).Although the software has been subjected to rigorous review,th'e USGS reserves the right to
update the software as needed pursuant to further analysis and review.No warranty,expressed'or
implied,is made by the USGS or the U.S.Government as to the functionality of the software and related
material norshall the fact of release constitute any such warranty.Furthermore,the software is released
on condition that neither the USGS nor the U.S.Government shall beheld liable for any damages
resulting from its authorized or unauthorized use.
USGS Product Names Disclaimer:Any use of trade;firm,or product nantes is for descriptive purposes
only and does not imply endorsement by the U.S.Government.
Application Version:4.2.1
•
•
https://streamstats.usgs.gov/ss/ 2/2
11/28/2018 StreamStats
X-SEC 6 FLOW DATA
Region ID: VA
Workspace ID: VA20181128192751791000
Clicked Point (Latitude, Longitude): 38.08294, -78.55336
Time: 2018-11-28 14:28:09 -0500
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Basin Characteristics
Parameter Code Parameter Description Value Unit
DRNAREA Area that drains to a point on a stream 2.73 square miles
Peak-Flow Statistics Parameters[Blue Ridge 2011 5144]
Parameter Code Parameter Name Value Units Min Limit Max Limit
DRNAREA Drainage Area 2.73 square miles 0.06 7866
Peak-Flow Statistics Flow Report[Blue Ridge 2011 5144]
https://streamstats.usgs.gov/ss/ 1/2
11/28/2018 StreamStets '
PII: Prediction Interval-Lower, Plu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE:
Standard Error (other -- see report)
Statistic Value Unit SEp
•
2 Year.Peak Flood 273 ft"3/s 17
2 33 Year Peak Flood 323 ft^3/s 18
5 Year Peak,Flood 604 ft"3/s 20
10 Year Peak.Flood 936 ft"3/s 24 •
25 Year Peak Flood 1470 ft"3/s 29 '
50 Year Peak Flood 1990 ft"3/s 32
100 Year Peak Flood 2770 ft"3/s 30
200 Year Peak Flood 3500 ft"3/s 33 •
Peak-Flow Statistics Citations
Austin, S.H., Krstolic, J.L., and Wiegand, Ute,2011, Peak-flow characteristics of Virginia
streams: U.S. Geological Survey Scientific Investigations Report 2011-5144, 106 p. + 3
tables and 2 appendixes on-CD.,(http://pubs:usgs.gov/sir/2011/5144/)
•
•
USGS Data Disclaimer:Unless otherwise stated,all data,metadata and related materials are considered
to satisfy the quality standards relative to the purpose for which the data were collected.Although these
data and associated'metadata have been reviewed for accuracy and completeness and approved for
release by the U.S.Geological Survey(USGS),no warranty expressed or implied is made regarding the
display or utility of the data for other purposes,nor on all computer systems,nor shall the act of
distribution constitute any such warranty.
USGS Software Disclaimer:This software has been approved for release by the U.S.Geological Survey
(USGS).Although the software has been subjected to rigorous review,the USGS reserves the right to
update the software as needed pursuant to further analysis and review.No warranty,expressed or
implied,is made by the USGS or the U.S..Government as to the functionality of the software and related
material nor shall the fact of release constitute any such warranty.Furthermore,the software is released
on condition that neither the'USGS nor the U.S.Government shall be held liable for any damages
resulting from its authorized or unauthorized use.
USGS Product Names Disclaimer:Any use of trade,firm,'br product names is for descriptive purposes
only and does not imply endorsement by the U.S.Government.,
Application Version:4.2.1 •
•
•
•
https://streamstats.usgs.gov/ss/ - 2/2
11/28/2018 StreamStats
X SEC 8 FLOW DATA
Region ID: VA
Workspace ID: VA20181128192053877000
Clicked Point (Latitude, Longitude): 38.08505, -78.55662
Time: 201 8-1 1-28 14:21 :1 1 -0500
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Basin Characteristics
Parameter Code Parameter Description Value Unit
DRNAREA Area that drains to a point on a stream 1 .14 square miles
Peak-Flow Statistics Parameters Blue Ridge 2011 5144]
Parameter Code Parameter Name Value Units Min Limit Max Limit
DRNAREA Drainage Area 1 .14 square miles 0.06 7866
Peak-Flow Statistics Flow Report[Blue Ridge 2011 5144]
https://streamstats.usgs.gov/ss/ 1/2
11/28/2018 StreamStets
PII: Prediction Interval-Lower, Plu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE:
Standard Error (other -- see report)
Statistic Value Unit SEp
2 Year Peak Flood 147 ft"3/s 17
2 33 Year Peak Flood 175 ft^3/s 18
5 Year Peak Flood 337 ft"3/s 20
10 Year Peak Flood 532 ft"3/s 24
25 Year Peak Flood 849 ft^3/s 29
50 Year Peak Flood 1160 ft"3/s 32
100 Year Peak Flood 1650 ft"3/s 30
•
200 Year Peak Flobd 2100 • ft"3/s 33
Peak-Flow Statistics,Citations
Austin, S.H., Krstolic, J.L., and Wiegand, Ute,2011, Peak=flow characteristics of Virginia
streams: U.S. Geological Survey Scientific Investigations Report 2011-5144, 1.06 p. + 3
tables and 2 appendixes on CD. (http://pubs.usgs.gov/sir/2011/5144/)
•
•
USGS Data Disclaimer:Unless otherwise stated,all data,metadata and related materials are considered
to satisfy the quality standards relative to the purpose forwhich the data were collected.Although these
data and associated metadata have been reviewed for accuracy and completeness and approved for
release by the U.S.Geological Survey(USGS),no warranty expressed or implied is made regarding the
display or utility of the data for other purposes,nor on all computer systems,nor shall the act of
distribution constitute any such warranty.
• USGS Software Disclaimer:This software has been approved for release by the U.S..Geological Survey •
(USGS).Although the software has been subjected to rigorous review,the USGS reserves the right to.
update the software as needed pursuant to further analysis and review.No warranty,expressed or
implied,is made by the USGS or the U.S.Government as to the functionality of the software and related
material nor shall the fact of release constitute any such warranty.Furthermore,the software is released
on condition that neither the USGS nor the U.S.Government shall beheld liable for any damages
resulting from its authorized or unauthorized use.
USGS Product Names Disclaimer:Any use of trade,firm,or product names is for descriptive purposes
only and does not imply endorsement by the U.S.Government.
Application Version:4.2.1
https://streamstats.usgs.gov/ss/ 2/2
11/28/2018 StreamStats
X-SEC 10 FLOW DATA
Region ID: VA
Workspace ID: VA20181128192443007000
Clicked Point (Latitude, Longitude): 38.07941, -78.55778
Time: 2018-11-28 14:25:00 -0500
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Basin Characteristics
Parameter Code Parameter Description Value Unit
DRNAREA Area that drains to a point on a stream 1 .4 square miles
Peak-Flow Statistics Parameters[Blue Ridge 2011 51441
Parameter Code Parameter Name Value Units Min Limit Max Limit
DRNAREA Drainage Area 1 .4 square miles 0.06 7866
Peak-Flow Statistics Flow Report[Blue Ridge 2011 5144]
https://streamstats.usgs.gov/ssl 1/2
11/28/2018 StreamStats
PII: Prediction Interval-Lower, Plu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE:
Standard Error (other -- see report)
Statistic Value Unit SEp
2 Year Peak Flood 170 ft^3/s 17
2 33 Year Peak Flood 202 ft"3/s 18
5 Year Peak Flood 387 ft"3/s 20
10 Year Peak Flood 607 ft^3/s 24
25 Year Peak Flood 966 ft^3/s 29
50 Year Peak Flood 1320 ft^3/s 32
100 Year Peak Flood 1860 ft"3/s 30
200 Year Peak Flood 2360 ft^3/s 33
Peak-Flow Statistics Citations
Austin, S.H., Krstolic, J.L., and Wiegand, Ute,2011, Peak-flow characteristics of Virginia
streams: U.S. Geological Survey Scientific Investigations Report 2011-5144, 106 p. + 3
tables and 2 appendixes on CD. (http://pubs.usgs.gov/sir/2011/5144/)
USGS Data Disclaimer:Unless otherwise stated,all data,metadata and related materials are considered
to satisfy the quality standards relative to the purpose for which the data were collected.Although these
data and associated metadata have been reviewed for accuracy and completeness and approved for
release by the U.S.Geological Survey(USGS),no warranty expressed or implied is made regarding the
display or utility of the data for other purposes,nor on all computer systems,nor shall the act of
distribution constitute any such warranty.
USGS Software Disclaimer:This software has been approved for release by the U.S.Geological Survey
(USGS).Although the software has been subjected to rigorous review,the USGS reserves the right to
update the software as needed pursuant to further analysis and review. No warranty,expressed or
implied,is made by the USGS or the U.S.Government as to the functionality of the software and related
material nor shall the fact of release constitute any such warranty. Furthermore,the software is released
on condition that neither the USGS nor the U.S.Government shall be held liable for any damages
resulting from its authorized or unauthorized use.
USGS Product Names Disclaimer:Any use of trade,firm,or product names is for descriptive purposes
only and does not imply endorsement by the U.S.Government.
Application Version:4.2.1
RECEIVED
MAY 1 3 7' 1
COMMUNITY
DEVELOPMENT
https://streamstats.usgs.gov/ss/ 2/2