HomeMy WebLinkAboutWPO202200005 Study 2022-11-15Castalia Farm Winery Stream Crossing Analysis
Existing Stream Conditions
In order to determine the requirements for flood control at the proposed stream crossing for
the entrance on Stony Point Pass, the existing flood conditions at the stream were analyzed. The flow
rates for the stream were determined using the culvert regression method which is best applied to large
drainage areas like this. The drainage area to the stream at this point is 456.6 ac. The corresponding
flow rates are shown in the table below:
Ct1!!ZrtA
A E
1156.6 Ac 1010 ft 9215
1). 1.75
Southern Piedmont Regression Equations
Storm
I Multiple -Parameter
Drainage-Area-Onty
Q,
214A"T"L"'
108.2 cfs
122(A)aos
98.5 cfs
Q10
38.8AO "E' 379 L 0.430
315.6 cfs
335(A)0'596
273.9 cfs
Q,,
54.11A"O"'L"
478.1 cfs
504(A)"'
414.2 cfs
Q�
74.3A .. E' 3M L � 495
626.4 cfs
661(A)o 170
54S.3 cfs
Q1M
101AOM9 E 03no.sn
788.1 cfs
849(A)""
703.0 cfs
The flow rate was also modelled using TR-55 since a second method is required to
determine flow rates for drainage areas over 20 acres. The 10-yr flow rate using this method was
calculated to be 332.04 cfs.
Hydrograph
350 332.
j ........... Irype: 11 "r 1"R
300 1 -Raintall-5.34-
_3 2 1 1
[' i4cfs
----------
250 Runo" Depth=1.15*
4 ..... --------- --------
200 r,in
j L Table
2 150
-----------
100
Print
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so
Export
0 0 5 10 15 2 1 0 2 . 5 3 . D 3 1 5 4 . 0 4'5 Edk
Time (hours) Help
Using the 10-yr flow rate calculated by TR-55 to be more conservative, the stream crossing was
analyzed in Hydraulic Toolbox using survey data to generate a section of the stream at the proposed
entrance location:
Tailwater/Channel Cross Section
Z' M-I
54T5
—5470
C
0
546 5
LU b4b 0
5455
Station (ft)
When the 10-yr storm calculation was performed, the depth in the channel is 3.196' which
overtops the bank and floods Stony Point Pass.
549
548
C:
0
m> 547
a)
W
IM, lei
545
Stream Crossing Design
Cross Section
U 10 1
Station (ft)
Since Stony Point Pass currently floods during the 10-yr storm, the stream crossing was designed
to allow for overflow to remain onsite and flow over the new access road. A Contech aluminum box
culvert will be installed in the stream and overflow is diverted onto the access road at a max depth of
12". HY-8 was used to calculate the overflow depth and model the section view below:
0
W
Crossing: Crossing I
Frout V� (Nato scak)
Station (ft)
By a I lowing excess runoff to flow over the access road, the current flooding onto Stony Point
Pass will be reduced.