HomeMy WebLinkAboutWPO202000004 Calculations 2020-08-17BROOKHILL STORMWATER MANAGEMENT
CALCULATIONS PACKET
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Flu 3 �OTIC Mo COLLIN sY
s 035701
`S NA L T,146L
(Blocks 9-11)
Date of Calculations
NOVEMBER 21, 2018
Revised on
DECEMBER 13, 2019
Revised on
AUGUST 41 2020
APPROVED
by the Albemarle County
Communityy DevgIoppment Department
Date 8N7/2U20
File WP0202000004
PREPARED BY:
COLLINS mINIGINEERING
200 GARRETT STREET, SUITE K
CHARLOTTESVILLE, VA 22902
434.293.3719 PH
434.293.2813 FX
www.collins-engineering.com
Summary of Changes:
1. The cover sheet was updated to include a date/seal matching the current set of plans.
2. The cover sheet for the VRRM water quality calculations was updated to include a 'summary'. No
revisions were made to this packet's previously reviewed/accepted VRRM water quality
calculations.
SCS TR-55 Calculations for Blocks 9-11
Soils Table for Blocks 9-11 (Source: NRCS Web Soil Survey Online Database)
Albemarle County, Virginia (VA003)
Albemarle County, Virginia (VA003)
Map Unit
Map Unit Name
percent of
Symbol
AOI
27B
Elioak loam, 2
22.1%
to 7 percent
slopes
27C
Elioak loam, 7
13.1%
to 15 percent
slopes
34C
Glenelg loam, 7
6.4%
to 15 percent
slopes
34D
Glenelg loam,
8.8%
15 to 25
percent slopes
39D
Hazel loam, 15
46.6%
to 25 percent
slopes
95
Wehadkee silt
3.0%
loam
Totals for Area of
100.00/0
Interest
Note: Soils' properties witin this development are predominantly composed of hydrologic type B
soils.
Precipitation Data
(Source: NOAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14
Point Precipitation Frequency Estimates)
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6.2 i .. runtla Rd
POINT PRECIPITATION FREQUENCY (PF) ESTIMATES
WITH 90% CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION
NOAA Atlas 14, Volume 2, Version 3
PDS-based precipitation frequency estimates with 90%, confidence intervals in inches)'
Average re°arence wlen4 (ye )
WratlonOOO
10 25 ® 100 ®® 1000
2--0;
(2W 7) (8.254.08) (4: 4510) (4_88b.14) (5.95-7.59) (6.868.69) 11 (7.839.99) 11 (8.87-11A) 11 (18 6) 11 (rib- 5.4)
U.S. Department of Agriculture
Natural Resources Conservation Service
Project: Brookhill
Location: Blocks 9-11
Check One: Present X Developed
1. Runoff curve Number (CN)
TR 55 Worksheet 2: Runoff Curve Number and Runoff
Designed By: FGM, PE
Checked By: SRC, PE
FL-ENG-21A
06/04
Date: 12/13/2019
Date: 12/13/2019
Cover description
CN (weighted) _
Drainage Area
Soil name and hydrologic
(Cover type, treatment, and hydrologic condition; percent
CN
Area
Product of CN x
total product/
Calculated'S'
Description
group (Appendix A)
(Acres)
Area
Value
impervious; unconnected/ connected impervious area ratio)
total area
DA 1
Impervious Areas
98
0.44.
43.4
B
Lawns in Good Condition (25%+/-)
61
1.50
91.5
60
6.74
(Pre-Dev.)
Woods in Good Condition (75%+/-)
55
3.99
219.3
Impervious Areas
98
0.00
0.0
DA 2
(Pre-Dev.)
B
Lawns in Good Condition (25%+/-)
61
1.61
97.9
57
7.60
Woods in Good Condition (75%+/-)
55
1 3.67
201.6
Impervious Areas
98
0.00
0.0
DA 3
B
Lawns in Good Condition (25%+/-)
61
1.00
60.8
57
7.70
(Pre-Dev.)
Woods in Good Condition (75%+/-)
55
2.99
164.6
DA 1
Impervious Areas
98
1.49
146.5
(Post-Dev.)
B
Lawns In Good Condition
61
0.56
33.9
88
1.37
Woods in Good Condition
55
0.00
0.0
Impervious Areas
98
2.80
274.8
DA 2
8
Lawns in Good Condition
61
2.79
170.0
80
2.57
(Post-Dev.)
Woods in Good Condition
55
0.00
0.0
Impervious Areas
98
2.76
270.3
DA 3
B
Lawns in Good Condition
61
4.07
248.4
74
3.52
(Post-Dev.)
Woods in Good Condition
55
0.72
39.6
2. Runoff
1-Year Storm
2-Year Storm
30-Year Storm
Drainage Area Description
Frequency -years
1
2
10
n a
Rainfall,. P (24 hour)- inches
3.00
3.62
5.47
n/a
Runoff, Q- inches
0.32
0.57
1.56
DA 1(Pre-Dev.)
Runoff, Q- inches
0.24
0.45
1.35
DA 2 (Pre-Dev.)
Runoff, Q- inches
0.23
0.44
1.33
DA 3 (Pre-Dev.)
Runoff, Q- inches
1.82
2.38
4.11
DA 1(Post-Dev)
Runoff, Q- inches
1.22
1.70
3.26
DA 2 (Post-Dev.)
Runoff, Q- inches
1 0.91
1 1.32
1 2.74
IDA 3 (Post-Dev)
U.S. Department of Agriculture
Natural Resources Conservation Service
TR 55 Worksheet 3: Time of Concentration (TJ or Travel Time (TJ
Project: Brookhill
Location: Blocks 9-11
Check One: Present X Developed X
Check One: Tc X T,
Segment ID:
Sheet Flow: (Applicable to T, only)
1 Surface description (Table 3-1)
2 Manning's roughness coeff., n (Table 3-1
3 Flow length, L (total L < 100) (ft)
4 Two-year 24-hour rainfall, Pi (in.)
5 Land slope, s (ft/ft)
6 Compute Tr = [0.007(n*L)°'a] / Pz .5 s°.a
Shallow Concentrated Flow
Designed By: FGM, PE
Checked By: SRC, PE
Through subarea n/a
FL-ENG-21A
06/04
Date: 12/13/2019
Date: 12/13/2019
DA1
DA2
DA3
DA1
DA2
DA3
(Pre-Dev.)
(Pre-Dev.)
(Pre-Dev.)
(Post-Dev.)
(Post-Dev.)
(Post-Dev.)
Dense
Dense
Dense
Dense
Dense
Dense
Grass
Grass
Grass
Grass
Grass
Grass
0.24
0.24
0.24
0.24
0.24
0.24
100
100
100
45
40
90
3.62
3.62
3.62
3.62
3.62
3.62
0.06
0.06
0.06
0.18
0.03
0.09
0.144
0.14
0.144
0.05
0.10
0.11
7 Surface description (paved or unpaved)
Unpaved
Unpaved
Unpaved
Paved
Unpaved
8 Flow Length, L (ft)
290
375
275
55
75
9 Watercourse slope, s (ft/ft)
0.16
0.11
0.18
0.04
0.24
10 Average velocity, V (Figure 3-1) (ft/s)
6.5
5.4
6.9
4.1
8.0
11 T,=L/3600*V
0.012
0.02
0.011
0.00
0.00
Channel Flow:
12 Cross sectional flow area, a (ft)
13 Wetted perimeter, P. (ft)
14 Hydraulic radius, r= a/Pw (ft)
15 Channel Slope, s (ft/ft)
16 Manning's Roughness Coeff, n
17V=[1.49r2"s"]/n
18 Flow length, L (ft)
19 Ti= L/ 3600*V
20 Watershed or subarea T, or T,
(Add Tt in steps 6, 11 and 19)
Note: The shoretest SCS Tc is 0.10 hrs.
c
3
�
0
LL
3
O
LL
d
LL
c w
c
m a
�
c w
m n
L d
u C
L LL
r
0
0
0
0
O
o
in
N
V
Up
0.00
0.01
0.01
0.16 0.16 0.16 0.10 0.12 0.12
U.S. Department of Agriculture
Natural Resources Conservation Service
Project:
Location:
Check One:
Brookhill
Blocks 9-11
Present X Developed X
TR 55 Worksheet 4: Graphical Peak Discharge Method
Designed By: FGM, PE
Checked By: SRC, PE
Date: 12/13/2019
Date: 12/13/2019
1. Data
Drainage Area Description
Drainage Area Description
Drainage Area Description
Drainage Area Description
Drainage Area Description
Drainage Area Description
DA1
(Pre-Dev.)
DA2
(Pre-Dev.)
DA3
(Pre-Dev.)
DA1
(Post-Dev.)
DA2
(Post-Dev.)
DA3
(Post-Dev.)
Drainage Area (Ann) In miles' =
0.0093
0.0082
0.0062
0.0032
0.0087
0.0118
Runoff curve number CN=
60
S7
57
88
80
74
Time of concentration (Tc)=
0.16
0.16
0.16
0.10
0.11
0.12
Rainfall distribution type=
II
It
II
II
If
n
Pond and swamp areas spread
throughout the watershed=
0
0
0
0
0
0
2. Frequency -years
1
2
10
1
2
10
1
2
10
1
2
10
1
2
10
1
2
10
3. Rainfall, P (24 hour)- inches
3.00
3.62
5.47
3
3.62
5.47
3.00
3.62
5.47
3.00
3.62
5.47
3.00
3.62
5.47
3.00
3.62
5.47
4. Initial Abstraction, la -inches
1.35
1.35
1.35
1.52
1.52
1.52
1.54
1.54
1.54
0.27
0.27
0.27
0.51
0.51
0.51
0.70
0.70
0.70
5. Compute la/P
0.45
0.37
0.25
0.51
0.42
0.28
0.51
0.43
0.28
0.09
0.08
0.05
0.17
0.14
0.09
0.23
0.19
0.13
6. Unit peak discharge, Qu- ¢mtn
550
675
825
400
600
800
400
Goo
Soo
1000
1000
1000
950
975
975
900
925
950
7. Runoff, Qfrom Worksheet 2- Inches
0.32
0.57
1.56
0.24
0.45
1.35
0.23
0.44
1.33
1.82
2.38
4.11
1.22
1.70
3.26
0.91
1.32
2.74
8. Pond and Swamp adjustment factor, Fp
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
9. Peak Discharge, Qp- cfs
where Qp=Qu Am QFp
1.66
3.58
11.95
0.80
2.25
8.90
0.58
1.66
6.62
Routed Through
UGD System
10.14
14.48
27.80
Routed Through
Wet Pond
WATERSHED SUMMARY FOR SUBAREA 1
Area,
1-year Flow,
2-year Flow,
10year Flow,
CN
ac.
ds
ds
cfs
DA 1(Pre-Dev.)
60
5.93
1.66
3.58
11.95
DA 1(Post-Dev.)
88
2.05
0.23
2.19
9.01
WATERSHED SUMMARY FOR SUBAREA 2
Area,
1-year Flow,
2-year Flow,
10year Flow,
ON
ac.
cfs
ds
ds
DA 2 (Pre-Dev.)
57
5.27
0.80
2.25
8.90
DA 2 (Post-Dev.)
80
5.59
10.14
14.48
27.80
WATERSHED SUMMARY FOR SUBAREA 3
Area,
1-year Flow,
2-year Flow,
10year Flow,
ON
ac.
cfs
ds
ds
DA 3(Pre-Dev.)
57
3.99
0.58
1.66
6.62
DA 3 (Post-Dev.)
74
7.55
0.12
0.60
4.16
9 VAC 25-870-66 (Point of Interest #1)
Section B: Channel Protection
"Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet
the criteria in subdivision 1, 2 or 3 of this subsection..."
Section B.1: Manmade stormwater conveyance systems
"When stormwater from a development is discharged to a manmade stormwater conveyance system,
following the land -disturbing activity, either..." a. or b. shall be met:
Section B.1.b.
"The peak discharge requirements for concentrated stormwater flow to natural stormwater conveyance
systems in subdivision 3 of this subsection shall be met."
Section B.3
"... the maximum peak flow rate from the one-year 24-hour storm following the land -disturbing activity
shall be calculated either.." a. or b."
Section B.3.a.
In accordance with the following methodology:
Q Allowed !c I.F. * (Q Pre -Developed * (RV Pre -Developed) ) I (RV Developed)
Q Allowed
Where: Q Pre -Developed =
CN Pre -Developed =
S Pre -Developed =
RV Pre -Developed=
CN Post -Developed =
S Post -Developed =
RV Post -Developed=
I. F. =
Q Developed
< 0.24 cfs
Section B.4 Limits of Analysis
1.66 cfs
(From Worksheet 4 Watershed Summary)
60
(From Worksheet 4 Watershed Summary)
6.74
(From SCS TR-55 eq. 2-4)
0.32 in.
(From SCS TR-55 eq. 2-3)
88
(From Worksheet 4 Watershed Summary)
1.37
(From SCS TR-55 eq. 2-4)
1.82 in.
(From SCS TR-55 eq. 2-3)
0.80
(Factor of Safety)
0.23 cfs
The analysis terminates at the onsite subarea since subsection B.3.a is met.
9 VAC 25-870-66 (Point of Interest #1)
Section C: Flood Protection
"Concentrated stormwater flow shall be released into a stormwater conveyance system and
shall meet one of the following criteria as demonstrated by use of acceptable hydrologic and
hydraulic methodologies:"
Section C.2.b.:
The point of discharge (the site outfall), "releases a postdevelopment peak flow rate for the
10-year 24-hour storm event that is less than the predevelopment peak flow rate from the
10-year 24-hour storm event. Downstream stormwater conveyance systems do not require
any additional analysis to show compliance with flood protection criteria if this option is
utilized."
10-Year, 24-Hour Pre -Development Subarea 1 Peak Flow Rate = 11.95 cfs
10-Year, 24-Hour Post -Development Subarea 1 Peak Flow Rate = 9.01 cfs
Section C.3 limits of Analysis
The flood protection analysis terminates at the subarea since subsection C.2.b is met.
9 VAC 25-870-66 (Point of Interest #2)
Section B: Channel Protection
"Concentrated stormwater flow shall be released into a stormwater conveyance system and
shall meet the criteria in subdivision 1, 2 or 3 of this subsection..."
Section B.1: Manmade stormwater conveyance systems
"When stormwater from a development is discharged to a manmade stormwater conveyance
system, following the land -disturbing activity, either..." a. or b. shall be met:
Section B.i.a.
"The manmade stormwater conveyance system shall convey the postdevelopment peak flow
rate from the two-year 24-hour storm event without causing erosion of the system."
Section B.4 Limits of Analysis
"stormwater conveyance systems shall be analyzed for compliance with channel protection
criteria to a point where either.." a. or b. are met
Section B.4.a.
"Based on land area, the site's contributing drainage area is less than or equal to 1.0% of the
total watershed area;"
9 VAC 25-870-66 (Point of Interest #2)
Section C: Flood Protection
"Concentrated stormwater flow shall be released into a stormwater conveyance system and
shall meet one of the following criteria as demonstrated by use of acceptable hydrologic and
hydraulic methodologies:"
Section C.2.a.:
The point of discharge (the site outfall), "confines the postdevelopment peak flow rate from
the 10-year 24-hour storm event within the stormwater conveyance system to avoid the
localized flooding."
Section C.3.c Limits of Analysis
The flood protection analysis terminates at the site outfall because, "the stormwater
conveyance system enters a mapped floodplain."
9 VAC 25-870-66 (Point of Interest #3)
Section B: Channel Protection
"Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet
the criteria in subdivision 1, 2 or 3 of this subsection..."
Section B.1: Manmade stormwater conveyance systems
"When stormwater from a development is discharged to a manmade stormwater conveyance system,
following the land -disturbing activity, either..." a. or b. shall be met:
Section B.1.b.
"The peak discharge requirements for concentrated stormwater flow to natural stormwater conveyance
systems in subdivision 3 of this subsection shall be met."
Section B.3
"... the maximum peak flow rate from the one-year 24-hour storm following the land -disturbing activity
shall be calculated either.." a. or b."
Section B.3.a.
In accordance with the following methodology:
Q Allowed !c I.F. * (Q Pre -Developed * (RV Pre -Developed) ) I (RV Developed)
Q Allowed
Where: Q Pre -Developed =
CN Pre -Developed =
S Pre -Developed =
RV Pre -Developed=
CN Post -Developed =
S Post -Developed =
RV Post -Developed =
I.F. =
Q Developed
< 0.12 cfs
Section B.4 Limits of Analysis
0.58 cfs
(From Worksheet 4 Watershed Summary)
57
(From Worksheet 4 Watershed Summary)
7.70
(From SCS TR-55 eq. 2-4)
0.23 in.
(From SCS TR-55 eq. 2-3)
74
(From Worksheet 4 Watershed Summary)
3.52
(From SCS TR-55 eq. 2-4)
0.91 in.
(From SCS TR-55 eq. 2-3)
0.80
(Factor of Safety)
0.12 cfs
The analysis terminates at the onsite subarea since subsection B.3.a is met.
9 VAC 25-870-66 (Point of Interest #3)
Section C: Flood Protection
"Concentrated stormwater flow shall be released into a stormwater conveyance system and
shall meet one of the following criteria as demonstrated by use of acceptable hydrologic and
hydraulic methodologies:"
Section C.2.b.:
The point of discharge (the site outfall), 'releases a postdevelopment peak flow rate for the
10-year 24-hour storm event that is less than the predevelopment peak flow rate from the
10-year 24-hour storm event. Downstream stormwater conveyance systems do not require
any additional analysis to show compliance with flood protection criteria if this option is
utilized."
10-Year, 24-Hour Pre -Development Subarea 3 Peak Flow Rate = 6.62 cfs
10-Year, 24-Hour Post -Development Subarea 3 Peak Flow Rate = 4.16 cfs
Section C.3 Limits of Analysis
The flood protection analysis terminates at the subarea since subsection C.2.b is met.
Underground Detention System
Routing Calculations
BH Blocks 9-11- UGD System
BasinFlow printout
INPUT:
Basin: BH Blocks 9-11 UGD System- Subarea 1
0 Contour Areas
Elevation(ft) Area(sf) Computed Vol.(cy)
1 Storage Pipes
Storage pipe 0
name:
Detention Piping
diameter (in)
120.000
length (ft)
120.000
invert (ft)
431.000
angle
0.287
volume (cy)
349.066
Start—Elevation(ft)
431.00 Vol.(cy) 0.00
7 Outlet Structures
Outlet structure 0
Orifice
name: Outlet Pipe
area (sf) 1.767
diameter or depth (in) 18.000
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 430.980
multiple 1
discharge out of riser
Outlet structure 1
Orifice
name: Low -Flow Orifice in Weir Plate
area (sf)
0.022
diameter or depth (in)
2.000
width for rect. (in)
0.000
coefficient
0.500
invert (ft)
431.000
multiple
1
discharge into
riser
Page 1
Outlet structure 2
Orifice
BH Blocks 9-11- UGD System
name: Mid -Flow Orifice in Weir Plate
area (sf)
0.196
diameter or depth (in)
6.000
width for rect. (in)
0.000
coefficient
0.500
invert (ft)
438.000
multiple
3
discharge into
riser
Outlet structure 3
Orifice
name: High -Flow Orifice in Weir Plate
area (sf)
0.196
diameter or depth (in)
6.000
width for rect. (in)
0.000
coefficient
0.500
invert (ft)
438.750
multiple
2
discharge into
riser
Outlet structure 4
Orifice
name: Over -Flow Weir
area (sf) 1.022
diameter or depth (in) 13.690
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 440.000
multiple 1
discharge into riser
Outlet structure 5
Weir
name:
Access MH at Weir Plate
diameter (in)
36.000
side angle
0.000
coefficient
3.300
invert (ft)
442.500
multiple
1
discharge
into riser
transition at (ft)
0.912
orifice coef.
0.500
orifice area (sf)
7.069
Page 2
BH Blocks 9-11- UGD System
Outlet structure 6
Orifice
name: Bypass Pipe
area (sf) 0.785
diameter or depth (in) 12.000
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 439.000
multiple 1
discharge out of riser
3 Inflow Hydrographs
Hydrograph 0
SCS
name:
Area (acres)
CN
Type
rainfall, P (in)
time of conc. (hrs)
time increment (hrs)
time limit (hrs)
fudge factor
routed
peak flow (cfs)
peak time (hrs)
volume (cy)
Hydrograph 1
SCS
1-yr. 24-yr Peak SCS Method Design Storm
2.050
88.000
2
name: 2-yr
Area (acres)
CN
Type 2
rainfall, P (in)
time of conc. (hrs)
time increment (hrs)
time limit (hrs)
fudge factor
routed
peak flow (cfs)
peak time (hrs)
volume (cy)
3.000
0.1000
0.0200
36.000
1.00
true
4.730
11.917
500.713
24-yr Peak SCS Method Design Storm
2.050
88.000
3.620
0.1000
0.0200
36.000
1.00
true
6.187
11.917
654.990
Page 3
Hydrograph 2
SCS
name:
Area (acres)
CN
Type
rainfall, P (in)
time of conc. (hrs)
time increment (hrs)
time limit (hrs)
fudge factor
routed
peak flow (cfs)
peak time (hrs)
volume (cy)
OUTPUT:
BH Blocks 9-11- UGD System
10-yr. 24-yr Peak SCS Method Design Storm
2.050
88.000
2
5.470
0.1000
0.0200
36.000
1.00
true
10.710
11.917
1133.821
Routing Method: storage -indication
Hydrograph 0
Routing Summary of
inflow (cfs)
discharge (cfs)
water level (ft)
storage (cy)
Hydrograph 1
Routing Summary of
inflow (cfs)
discharge (cfs)
water level (ft)
storage (cy)
Hydrograph 2
Routing Summary of
inflow (cfs)
discharge (cfs)
water level (ft)
storage (cy)
Peaks: 1-yr. 24-yr Peak SCS Method Design Storm
4.707 at
11.92 (hrs)
0.230 at
12.56 (hrs)
437.973 at
12.72 (hrs)
247.395
Peaks: 2-yr. 24-yr Peak SCS Method Design Storm
6.158 at
11.92 (hrs)
2.186 at
12.08 (hrs)
438.862 at
12.08 (hrs)
283.095
Peaks: 10-yr. 24-yr
10.659 at
9.006 at
440.977 at
345.261
Thu Dec 05 09:05:29 EST 2019
Peak SCS Method Design Storm
11.92 (hrs)
11.96 (hrs)
11.96 (hrs)
Page 4
Level II Wet Pond
Routing Calculations
BH Blocks 9-11 Level II Wet Pond- Subarea 3
BasinFlow printout
INPUT:
Basin: BH Blocks 9-11 Level II Wet Pond- Subarea 3
8 Contour Areas
Elevation(ft)
Area(sf)
Computed Vol.(cy)
428.00
579.00
0.0
430.00
1545.00
75.8
432.00
2948.00
239.4
433.00
4175.00
370.7
434.00
6537.00
567.4
436.00
10163.00
1181.0
438.00
14374.00
2085.3
440.00
19395.00
3331.4
Start—Elevation(ft)
5 Outlet Structures
Outlet structure 0
Orifice
434.00 Vol.(cy) 567.42
name: Proposed Barrel
area (sf)
0.349
diameter or depth (in)
8.000
width for rect. (in)
0.000
coefficient
0.500
invert (ft)
429.020
multiple
1
discharge out
of riser
Outlet structure 1
Orifice
name: Low Flow Orifice
area (sf) 0.020
diameter or depth (in) 1.938
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 434.000
multiple 1
discharge into riser
Page 1
BH Blocks 9-11 Level II Wet Pond- Subarea 3
Outlet structure 2
Orifice
name: Mid Flow Orifice
area (sf) 0.196
diameter or depth (in) 6.000
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 436.500
multiple 5
discharge into riser
Outlet structure 3
Weir
name: Proposed Riser
diameter (in)
18.000
side angle
0.000
coefficient
3.300
invert (ft)
437.250
multiple
1
discharge
into riser
transition at (ft)
0.456
orifice coef.
0.500
orifice area (sf)
1.767
Outlet structure 4
Weir
name:
Proposed Emergency Spillway
length (ft)
25.000
side angle
0.000
coefficient
3.300
invert (ft)
438.250
multiple
1
discharge
through dam
4 Inflow Hydrographs
Hydrograph 0
SCS
name: 1-yr
SCS TR-55 24-hr Design Storm
Area (acres)
7.550
CN
74.000
Type 2
rainfall, P (in)
3.000
time of conc. (hrs)
0.1200
time increment (hrs)
0.0200
time limit (hrs)
30.000
fudge factor
1.00
routed
true
peak flow (cfs)
8.415
peak time (hrs)
11.922
volume (cy)
921.104
Page 2
BH Blocks 9-11 Level II Wet Pond- Subarea 3
Hydrograph 1
SCS
name: 2-yr
SCS TR-55 24-hr Design Storm
Area (acres)
7.550
CN
74.000
Type 2
rainfall, P (in)
3.620
time of conc. (hrs)
0.1200
time increment (hrs)
0.0200
time limit (hrs)
30.000
fudge factor
1.00
routed
true
peak flow (cfs)
12.261
peak time (hrs)
11.922
volume (cy)
1342.159
Hydrograph 2
SCS
name: 10-yr
SCS TR-55 24-hr Design Storm
Area (acres)
7.550
CN
74.000
Type 2
rainfall, P (in)
5.470
time of conc. (hrs)
0.1200
time increment (hrs)
0.0200
time limit (hrs)
30.000
fudge factor
1.00
routed
true
peak flow (cfs)
25.428
peak time (hrs)
11.922
volume (cy)
2783.470
Hydrograph 3
SCS
name: 100-yr
SCS TR-55 24-hr Design Storm
Area (acres)
7.550
CN
74.000
Type 2
rainfall, P (in)
8.970
time of conc. (hrs)
0.1200
time increment (hrs)
0.0200
time limit (hrs)
30.000
fudge factor
1.00
routed
true
peak flow (cfs)
53.752
peak time (hrs)
11.922
volume (cy)
5883.931
Page 3
BH Blocks 9-11 Level II Wet Pond- Subarea 3
OUTPUT:
Routing Method: storage -indication
Hydrograph 0
Routing Summary
of
Peaks: 1-yr SCS TR-55
24-hr Design Storm
inflow
(cfs)
8.400
at
11.92
(hrs)
discharge
(cfs)
0.120
at
15.70
(hrs)
water level
(ft)
436.218
at
18.34
(hrs)
storage
(cy)
1264.657
Hydrograph 1
Routing Summary
of
Peaks: 2-yr SCS TR-55
24-hr Design Storm
inflow
(cfs)
12.240
at
11.92
(hrs)
discharge
(cfs)
0.603
at
12.78
(hrs)
water level
(ft)
436.665
at
12.78
(hrs)
storage
(cy)
1447.264
Hydrograph 2
Routing Summary
of
Peaks: 10-yr SCS
TR-55 24-hr Design Storm
inflow
(cfs)
25.384
at
11.92
(hrs)
discharge
(cfs)
4.155
at
12.18
(hrs)
water level
(ft)
438.160
at
12.20
(hrs)
storage
(cy)
2171.369
Hydrograph 3
Routing Summary
of
Peaks: 100-yr
SCS
TR-55 24-hr Design Storm
inflow
(cfs)
53.659
at
11.92
(hrs)
discharge
(cfs)
47.273
at
11.98
(hrs)
water level
(ft)
438.897
at
11.98
(hrs)
storage
(cy)
2598.367
Mon Dec 09 12:06:43 EST 2019
Page 4
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Subarea 2- Riprap Lined Channel Calculations- 2-yr
Complex Channnel-
Subarea 2 Rirap Channel to Outlet Protection (2yr)
Input:
Slope
Flow (given)
line
x y
n
0
0.000 2.000
0.050
(first n value not used)
1
6.000 0.000
0.050
2
7.000 0.000
0.050
3
13.000 2.000
0.050
Output:
Depth
0.830
(y)
( 0.830)
Channel
bed
segment output:
line
Q V
A
P
1
4.36 4.22
1.03
2.62
2
5.76 6.94
0.83
1.00
3
4.36 4.22
1.03
2.62
Mon Dec 09 14:59:38 EST 2019
Page 1
Subarea 2- Riprap Lined Channel Calculations- 10-yr
Complex Channnel-
Subarea 2 Rirap Channel to Outlet Protection (10yr)
Input:
Slope
Flow (given)
line
x y
n
0
0.000 2.000
0.050
(first n value not used)
1
6.000 0.000
0.050
2
7.000 0.000
0.050
3
13.000 2.000
0.050
Output:
Depth
1.101
(y)
( 1.101)
Channel
bed
segment output:
line
Q V
A
P
1
9.28 5.10
1.82
3.48
2
9.24 8.39
1.10
1.00
3
9.28 5.10
1.82
3.48
Mon Dec 09 14:59:00 EST 2019
Page 1
1992
3.18
PIPE OUTLET CONDITIONS
A A
'IPE OUTLET TO FLAT
REA WITH NO DEFINED
'HANNEL
L a
d
SECTION A -A FILTER CLOTH KEY IN 8'-9': RECOMMENDED FOR ENTIRE PERIMETER
SECT]
FALTER CLOTH
3dD (MIN)
'IPE OUTLET TO WELL
IEFINED CHANNEL
I
d
KEY IN 6"-9": RECOMMENDED FOR ENTIRE PERIMETER
NOTES: 1. APRON LINING MAY BE RIPRAP, GROUTED RIPRAP, GABION
BASKET, OR CONCRETE.
2. La IS THE LENGTH OF THE RIPRAP APRON AS CALCULATED
USING PLATES 3.18-3 AND 3.18-4.
3. d = 1.5 TIMES THE MAXIMUM STONE DIAMETER, BUT NOT
LESS THAN 8 INCHES.
Source: Va. DSWC
Plate 3.18-1
III - 157
Stormwater Management Facilities'
Storm Sewer Calculations
Table 8: Pipe Design Table
PIPE DESIGN
n=0.013 for RCP
n=0.01 for
HDPE
pi"
Hydrology
Pipe
�
�
a
E
P
ma'E
s
3
8
e
g
b
t
=
s
RP run: 304-Out
304
W2
7
O.W
CM
4.5W
729.W
0.38
1.72
4.89
429.W
428.10
8.0
0.010
0.11W
8
4.44
14.W
0.01
N2
Out
0W
O.W
0.W0
4.5W
729.01
0.38
0.00
4.39
428.W
416.N
141.8
0.013
O.O
24
65.W
11.fi8
0.20
Pipe run: Urdegrourd
Detentbn (DGD)- Out
11GD
40B
2.05
O.W
1.2W
1.2W
144.N
1.22
1.W
4.70
4N.%
430.7e
5.0
0.010
0.0400
18
22.M
t0.N
0.01
40B
408
0.00
O.W
O.OW
2.4N
1M.11
1.a
O.N
9.01
430.BB
42321
85.3
0.013
0.1143
24
]fi.4B
1626
OID
40B
404
E.
0..
0.000
2.4E
144.18
122
0!
9.01
419.21
41422
31.2
0.013
0.1N0
N
90.49
1824
0.03
406
402
O.W
O.W
0.0W
2.4N
144.21
1.22
0.W
9.01
410.22
400.48
61.0
0.013
0.1N0
24
90.49
1824
0.W
402
Out
0.00
O.W
0.000
2.I
144.26
122
O.W
9.01
3%.W
3%.W
".0
0.013
0.02W
24
31.W
8.71
0.W
prun :' Byp-408
l-410
2.05
ON
1.2W
1.230
144.W
1.22
1.W
4.31
439.N
43820
5.0
0.010
0.1W0
12
15.41
16.81
ow
410
40B
O.W
O.W
0."
1.2W
144.N
1.22
O.W
4.31
4W.70
43588
48.1
0.010
0.0178
12
5.15
7.32
0.10
Design Year: 10
Hydraulic Grade Line Calculation
Project: BH Blks 9-1 l
Job #: 182150
Prepared by: FGM, PE
—�
11
m�
111
11
11
�_---_--_—__--
Hydraulic Grade Line Page 1
Virginia Runoff Reduction Method
Water Quality Calculations
Summary:
After the implementation of protected open spaces, this plan requires an overvall phosphorous
removal rate of 10.05 Ibs/yr. The proposed level II wet pond treating subarea 3 removes 5.87 Ibs/yr,
resulting in a remaining phosphorous removal balance of 4.18 Ibs/yr. This information can be found
in the following VRRM water quality calculations.
Also, a 2.08 Ibs/yr phosphorous removal credit for Wet Pond B is applied to this project. Wet Pond B
is located immediately adjacent to Block 11 and is associated with WPO 2001700037 Amendment #2.
Consequently, a minimum phosphorous removal rate purchase of 2.10 Ibs/yr is required with this
plan.
om I. aumj/aeauubn Me(ME New OevebpmmEeanpOon[e speatlsM1ees-Ver 34
02033 BMPSUndaNs and spetlllotlons 11MU dEBWShednhadspednatigo
pro)xs Name: B.MNIII Bb 9-11
Oate: 11/13/1019
Rmp oe,mn Sv+rNronomtiru 3013Drah51ds&Sped
Site Information
Post -Development Project (Treatment Volume and Loads)
land coves lased
F Soax
BSWk
c5ella
o5oik
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u.3a
ree.yapa..paQa..araaueam
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u.zz
rasemmeymanaBm
uu
t63
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ren/apentpesaimsmmhepremamtldaamName
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selgmmesl
a3
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iW
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nJ6
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ex pNaueMl
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pl lea mrnumhmrl
0.90
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0.
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ss.zz
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Starmvater Rest Menwmem Nattlm(RR=Runall Re uRbn
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va Pi
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Site Results (Water Quality Compliance)
Area Checks
D.A. A
DA. B
D.A. C
D.A. D
D.A. E
AREA CHECK
FOREST/OPEN SPACE (ac)
0.00
0.00
0.72
0.00
0.00
OK.
IMPERVIOUS COVER (ac)
0.00
0.00
2.76
0.00
0.00
OK.
IMPERVIOUS COVER TREATED (ac)
0.00
0.G0
2.76
0.00
0.00
OK.
MANAGED TURF AREA (ac)
0.00
0.00
4.07
0.00
0.00
OK.
MANAGEDTURFAREATREATED(ac)
0.00
0.00
4.07
0.00
0.00
OK.
AREA CHECK
Site Treatment Volume WA
Runoff Reduction Volume and TP By Drainage Area
D.A. C
I D.A. 0
D.A. E
TOTAL
RUNOFF REDUCTION VOLUME ACHIEVED (ft)j
0
0
0
0
TP LOAD AVAILABLE FOR REMOVAL (lb/yr)l
7.84
0.00
0.00
7.84
TP LOAD REDUCTION ACHIEVED (Ib/yr)
0.00
0.00
5.87
0.00
0.00
5.87
TP LOAD REMAINING (Ib/yr)
0.00
10.00
1.97
0.00
0.00L
1.97
NITROGEN LOAD REDUCTION ACHIEVED (Ib/yr)
E 22.40
Total Phosphorus
FINAL POST -DEVELOPMENT TP LOAD (Ib/yr)W1655
TP LOAD REDUCTION REQUIRED (Ib/yr)
TP LOAD REDUCTION ACHIEVED (Ib/yr)
TP LOAD REMAINING (Ib/yr):
REMAINING TP LOAD REDUCTION REQUIRED (Ib/yr):
4.18
Total Nitrogen (For Information Purposes)
POST -DEVELOPMENT LOAD(Ib/yr)
160.43
NITROGEN LOAD REDUCTION ACHIEVED (Ib/yr)
22.40
REMAINING POST -DEVELOPMENT NITROGEN LOAD (Ib/yr)
138.03
Runoff Volume and Curve Number Calculations
_ Enter design storm rainfall depths (in):
1-yearctorm 2-year storm 10-yearstorm
3W 113S, s.v
VseNMIAmarlil Mmeweascn rwvnOOY/frdr/pfrWf
"Hates (see below):
[])The curce numhers and runoff wlumes mmputed in this spreadsheet for each dainage area are Radium in their appliubllity for determining and demanso-adeg mmpllance with water quantity
requirements. See VRRM Osee, Guide and Documentation for addiommil information.
-
[al Runoff Volume IRV) for WeandpastArw op ram drainage areas must be in volumetric units leg., avetest or cubs, Feet) when udogthe Energy Balance Equation. Runoff measured In watershed -
inches and shown in the spreadsheet as RV(watershedinch) can Wily be used in the Ench, BalaMe Equation when the pre and postdevelopment drainage areas are equal. Otherwise RVlwatershed-chi
tin be muWplied by thedmim,mea.
-
[31 Adjusted ri sare based an runoff reduction volumes calculated In AA. tabs. An alternative EN adlusvnem calculation for V yemmd Ranh is included In BMP specification No. S.
Drainage Area Curve Numbers and Runoff Depths"
Curve numbers (CN, CNadj) and runoff depths (RVWw,,wm) are computed with and without redurtion practices.
Drainage Area ASoils aSells CSpils Dsuits real Area lae.eal: 0.00
Fmest/Open Spare— undisturbed, protected forest/open Area a res) G.W am AW AW Run.%Redu[[i
Vote or refarertN land [Nc 3B 55 ID A Volume ft3^ o
scattered Tuff seemed, graded for yaM or ather turf Arealaves) AOB ACB AW AW
m be mowed/man M 39 st JO B9
Impervious Cwer Arcalavv) o.W ACO AM AM
FN 9B 9B 98 98
011I.nN
0
1-yearstorm 2-year storm 10-yearstorm
RVo,,,yp,d htwee shed-MeAJ with no Runoff Reduction• ..an o.Bo no,
RVosveep.I(wdtersheE-InMJ wain Runoff RetluRion" TomR. Aw
Adjusted CN" o 0 0
"See Notes above
Omni Am.B ASoils Bsuits CSpils DSoils rota) Area laoaal: D.0p
Forest/Open Spare— undistuNed, protected Forest/.pen 1 Prea(avesl O.W 0. AW AW Ru— duction
Tote or refrertN land IMa 39 55 TI P Volumeh: o
MaregedI art—d@Nmered. ..cd norya.s he mr., an 1 turim rest AW aw Am AW
_
m be mowed/man w 39 BS rq BB
Impervious Cmer Aaabves ABB om a'. a'.
CN se 9B 9B 9B
CN,,& of
0
1-yearstorm 2-year storm 10-yearstorm
RVp,•,s,,g pV.wrsted-fach) with no Runoff RetluRion" Aw o.00 A00
RV�yop"d(watershed-Ineh)wi[M1 Runoff RetluRion• ono Woo ABo
Adjusted CN• o B d
'See Not. above
Drainage Areaf
Ports(/Open Spas-uMlamnd,-Ilortlbresr/open Mm srtm
ASoils
0.00
aSoils
A]J
CSoils
A00
DSoils
GOO
iota Arm laves):
RunoHReduetlon
7.55
rtfaRrtMland (N
30
55
]fl
1
Volume h':
0
Managetl Turf-d.rh d,gmled foryarols aoNer turf iArealava)
fobemowetl/man tl 1CN
!yea laves)
0.00
39
AOp
d.OJ
61
2]6
GM
]d
GW
GM
&1
GW
_
Impervious Cover CN
RVoe„Np,d (WafasheblMhf WRh no Runoff Reduction'
RVyNepag (werershN-/oNJ whh Runoff Reduction'
98
1-yearstorm
091
osl
98
2-rear storm
Y3J
L3l
96
larear storm
L]d
2]0
96
CN(ozq
]d
'Adjusted CN'
Jd
26
2A
'See Notes above
Drainage Area0
ASoils
aSails
CSoils
DSoils
Rohl arm laves):
0.00
Portst Open Spas-u.'. Rd, gotecled forest/open Nm avm
A00
Aw
GOO
GOO
Runoff ReEu[tlon
rtforertM land CN
30
55
ID
1
Volume k':
0
ManagedTurf-tluN? tl,8 dad for Vards or atbes turf Ajro)
m be mowadJmana CN
O.W
39
AM
51
Gon
]d
GM
&1
_
Impervious Cover Mm lavm)
LN
A00
99
"no
9B
GOO
98
GOO
98
CN,.A. of
0
RVo,,,yp,y (wmershed(wa) svRb no Runoff Reduction'
RVo.wiepm(wareshed-/M1) vnth RunvR Reduction'
'Adjusted CN'
1-year storm
0.0o
GOO
p
2-year storm
O.Ro
AdP
0
layear storm
Go0
Goo
0
'See Notes above
Dnrinr,e Area
Po—t/Open S,- urdluuNd, potected forest/open Mea(aves)
ASoih
0.00
BSails
0.00
CSoils
000
DSoils
000
Toml arm lavm):
RunoHReduetlon
0.00
space or reforn@d Ian tl CN
ManagedTurf- tli&.mrd,gradrdmrprdswatherturt grtavm
a
30
o.W
55
O.W
70
GOo
]]
GOo
Volume k':
0
m be mowed/mamgtl CN
39
61
]a
&1
Imperviom Cwm Area avm)
CN
0.W
98
0.00
9B
GO0
98
0.00
98
CN(ow E)
0
_
Pole (wmt sd-Inch) whh nv PunaN Reduction'
RVp�epm (wolershMin[h/wkh Runpff Reduction'
1-yearstorm
u,do
GOO
2-yearstorm
O.oO
AW
10-year storm
G00
GOo
IL
—Adjusted CN'
d
0
0
'See Notes above
Virginia Runoff Reduction Method Wodcsheet
DEq Virginia Runoff Reduction Method New Development Compliance Spreadsheet - Verslor 3.0
8MP Design Specifications List: 2013 Draft Stds & Specs
Site Summary
Total Rainfall= 43inches
Site Land Cover Summary
A soils
e5oils
CSoils
DSoils
Totals
%of Total
Forest/Open(acres)
0.00
11.34
0.00
0.00
11.34
38
Managed Turf (acres)
1 0.00
11.22
0.00
0.00
11.22
37
Impervious Cover (acres)
I 0.00
7.63
0.00
0.00
7.63
25
30.19
100
Site Tv and Land Cover Nutrient Loads
Site Rv
0.33
Treatment Volume Ra
35,fi93
TP Load (lb/yr)
22.43
TN Load (lb/yr)
360.43
Total TP Load Reduction Required (lb/yr) 10.05
Site Compliance Summary
Total Runoff Volume Reduction (ft)
0
Total TP Load Reduction achieved(lb/yr)
5.87
Total TN Load Reduction Achieved (lb/yr)
22.40
Remaining Post Development TP Load
16.55
(lb/yr)
Remaining TP Load Reduction (lb/yr)
4.18
Required
Summary Print
Virginia Runoff Reduction Method Wodcsheet
Drainage Area Summary
D.A. A
D.A. B
D.A. C
D.A. D
D.A. E
Total
Forest/Open (acres)
0.00
0.00
0.72
0.00
0.00
0.72
Managed Turf (acres)
0.00
0.00
4.07
0.00
0.00
4.07
Impervious Cover (acres)
0.00
0.00
2.76
0.00
0.00
2.76
Total Area (acres)
0.00
0.00
7.55
0.00
0.00
7.55
Drainage Area Compliance Summary
D.A. A
D.A. B
D.A. C
D.A. D
D.A. E
Total
TP Load Reduced (lb/yr)
1 0.00
0.00
5.87
0.00
0.00
5.87
TN Load Reduced (lb/yr)
1 0.00
0.00
22.40
0.00
0.00
22.40
Summery Print
Virginia Runoff Reduction Method Wodcsheet
Drainage Area C Summary
Land Cover Summary
ASolls
B5o115
CSolls
DSolis
Total
"/o of Total
Forest/Open (acres)
0.00
0.72
0.00
0.00
0.72
10
Managed Turf (acres)
1 0.00
4.07
0.00
1 0.00
4.07
54
Impervious Cover (acres)
1 0.00
2.76
0.00
1 0.00
2.76
37
7.55
BMP Selections
Managed Turf
Impervious
TP Load from
Downstream
BMP Treatment
Untreated TP Load
TP Removed
TP Remaining
Practice
Credit Area
[aver Credit
I
s
Volume (k)
Upstream
to Practice (Ibs)
(lb/yr)
(Ib/yr)
Treatment to be
acres
Area acres
Practices Ibs
Employed
13.c. Wet Pond g2(Spei N14)
4.07
2.76
12,472.68
0.00
7.83
5.87
1 1.96
Total Impervious Cover Treated(acres)
2.76
Total Turf Area Treated (acres)
4.07
Total TP Load Reduction Achieved in D.A.
(lb/yr)
5.87
Total TN Load Reduction Achieved in D.A.
(lb/yr)
22.40
Summery Print
Virginia Runoff Reduction Method Wodcsheet
Runoff Volume and CN Calculations
1-yearstorm 2-year storm 10-year storm
Target Rainfall Event (in) 1 3.00 3.62 S.47
Drainage Areas
RV & CN
Drainage Area A
Drainage Area B
Drainage Area C
Drainage Area D
Drainage Area E
CN
0
0
74
0
0
RR (ftal
0
0
0
0
0
1-year return period
RV wo RR lwsinl
0.00
0.00
0.91
0.00
0.00
RV w RR Iws-Inl
0.00
0.00
0.91
0.00
0.00
CN adjusted
0
0
74
0
0
2-year return period
RV wa RR (.In)
MOD
0.00
1.32
0.00
0.00
RVw RR(ws-In)
0.00
0.00
1.32
0.00
O.OD
CNadjusted
0
0
74
0
0
10-year return period
RV.RR(.In)
MOD
0.00
2.74
0.00
0.00
RVw RR Iws-Inl
0.00
0.00
2.74
0.00
0.00
CN adjuated
0
0
74
0
0
Summery Print
Culvert #1 Analysis
Soil$ Tab Ie for Culvert #1 (Source:NRCSWeb Soil Survey Online Database)
Albemarle County, Virginia (VA003)
Map
Unit
Map Unit Name
Acres
Percent of
Symbol
in AOI
AOI
27B
Elioak loam, 2
12.0
22.8%
to 7 percent
slopes
27C
Elioak loam, 7
11.3
21.5%
to 15 percent
slopes
34C
Glenelg loam,
2.3
4.3%
7 to 15 percent
slopes
34D
Glenelg loam,
0.3
0.6%
15 to 25
percent slopes
39C
Hazel loam, 7
0.0
0.0%
to 15 percent
slopes
39D
Hazel loam, 15
19.6
37.2%
to 25 percent
slopes
47D
Philomont
2.8
5.3%
sandy loam, 15
to 25 percent
slopes
65B
Pacolet sandy
2.0
3.8%
loam, 2 to 7
percent slopes
94C
Toast sandy
2.3
4.4%
loam, 7 to 15
percent slopes
Totals for Area of
52.6
100.0%
Interest
Note: Soils' properties witin this watershed are predominantly composed of hydrologic type B soils.
SCS TR-55 Calculations for Culvert #1
U.S. Department of Agriculture
Natural Resources Conservation Service
Project: Brookhill- Proposed Culvert
Location: Stella Lane Extension
Check One: Present X Developed X
1. Runoff curve Number (CN)
TR 55 Worksheet 2: Runoff Curve Number and Runoff
Designed By: FGM, PE
Checked By: SRC, PE
FL-ENG-21A
06/04
Date: 12/13/2019
Date: 12/13/2019
Soil name and
Cover description
CN (weighted) _
Drainage Area
hydrologic group
(Cover type, treatment, and hydrologic condition; percent
CN
Area
Product of CN
total product/
Calculated 'S'
Description
(Appendix A)
impervious; unconnected/ connected impervious area ratio)
(Acres)
xArea
total area
Value
Woods
55
55.00
3025
Culvert H1
B
Grass
61
3.00
183
57
7.52
Impervious Areas
98
2.50
245
2. Runoff
10-Year Storm
25-Year Storm
100-Year Storm
I Drainage Area Description
Frequency -years
10
25
100
n/a
Rainfall, P(24 hour) -inches
5.5
6.7
9.0
n/a
Runoff, Q-inches
1.37
1 2.14
1 3.72
ICulvert##
U.S. Department of Agriculture
Natural Resources Conservation Service
TR 55 W orksheet 3: Time of Concentration (T,) or Travel Time (T,)
FL-ENG-21A
06/04
Project: Brookhill- Proposed Culvert Analysis
Designed By: FGM, PE Date: 12/13/2019
Location: Stella Lane Extension
Checked By: SRC, PE Date: 12/13/2019
Check One: Present X Developed X
Check One: T, X T,
Through subarea n/a
Culvert #1
Segment ID:
Sheet Flow: (Applicable to T, only)
Woods- Light
1 Surface description (Table 3-1)
Underbrush
2 Manning's roughness coeff., n (Table 3-1
0.4
3 Flow length, L (total L < 100) (ft)
100
4 Two-year 24-hour rainfall, Pr(in.)
3.7
5 Land slope, s (ft/ft)
0.05
6 Compute T,= [0.007(n'L)o.e] / Pins s°'a
0.23
Shallow Concentrated Flow:
7 Surface description (paved or unpaved)
Unpaved
8 Flow Length, L (ft)
700
9 Watercourse slope, s (ft/ft)
0.089
10 Average velocity, V (Figure 3-1) (ft/s)
4.8
11 T,= L / 3600•V
0.04
Channel Flow:
12 Cross sectional flow area, a (ft')
13 Wetted perimeter, P. (ft)
3
o
W ,�
14 Hydraulic radius, r=a/P.(ft)
m
15 Channel Slope, s (ft/ft)
s E
16 Manning's Roughness Coeff, n
U
o m
17 V= [ 1.49r� s°s ] / n
o '�
18 Flow length, L (ft)
19 T,= L / 3600-V
0.05
20 Watershed or subarea T,or T,
(Add T, in steps 6, 11 and 19)
0.32
U.S. Department of Agriculture
Natural Resources Conservation Service
Project: Brookhill- Proposed Culvert Analysis
Location: Stella Lane Extension
Check One: Present X Developed X
TR 55 Worksheet4: Graphical Peak Discharge Method
Designed By: FGM, PE
Checked By: SRC, PE
FL-ENG-21C
06/04
Date: 12/13/2019
Date: 12/13/2019
1. Data
Drainage Area
Description
Drainage Area
Description
Drainage Area
Description
Drainage Area
Description
Drainage Area
Description
Culvert #1
Drainage Area (Am) in miles' =
0.0945
Runoff curve number CN=
57
Time of concentration (Tc)=
0.32
Rainfall distribution type=
II
Pond and swamp areas spread
throughout the watershed=
0
2. Frequency -years
10 25 100
3. Rainfall, P (24 hour) -inches
5.47 6.72 8,97
4. Initial Abstraction, la- inches
1.50 1.50 1.50
5. Compute la/P
0.27 0.22 0.17
6. Unit peak discharge, Qu-csm/in
575 600 625
7. Runoff, Qfrom Worksheet 2- inches
1.37 2.14 3.72
8. Pond and Swamp adjustment factor, Fp
1 1 1
9. Peak Discharge, Qp- cfs
where Qp=Qu Am Q Fp
74.42 121.15 219.74
WATERSHED SUMMARY
CN Area, 10-year Flow, 25-year Flow, 100-year Flow,
ac. cfs cfs cfs
Culvert#1 1 57 60.50 74.42 121.15 219.74
Project Brookhill Neighborhood Blocks 9-11
Plan Sheet No.
Designer FGM, PE
Sheet 1 of 1
Rev. Date
Date 217/20
STATION:
AHW Controls
CROSSING #1
HYDROLOGICAL DATA
100 yr. Flood plain elev.
D.A. = 60.5 ac., CN - 57, TC -0.32 hrs.
Design AHW depth elev.
Structures elev.
ireq. TWelev.
Shoulder
=
elev. 440
CL elev. 440.4
Skew ° Cover
a.
ADT
Q 25 = 121.15 CFS
Q Design = 135 CFS
Detours Available
Overtopping Stage
Length
Q CFS
Flood Plain Management
Inv. El. 403.10 So= 3.04%
Inv. El. 395.50
_=
Q CFS
Criteria and Significant Impact
Orig. Gr. Elev. 403.6 L= 250
Orig. Gr. Elev. 396
_=
Q = CFS
CULVERT TYPE & SIZE
Q
Q/B
HEADWATER COMPUTATIONS
CONT.
HW.
ELEV.
OUTLET
VELOCITY
Treat.
COMMENTS
INLET CONT.
OUTLET CONTROL
HW/D
I HW
Ke
do
(dc+D)/2
he
H
LSo
HW
C.M.
Smooth
(1) - 5'x5' Box Culvert w/ 45° wingwalls
135
135
1
4.5
0.5
8.3
6.4
6.4
3.2
7.6
2.0
400.00
12.65
YES
Inlet Controlled
Note: Design assumes lower 6" is submerged
Design Flood Exceed. Prob.
_ Elev.
Overtop Flood Exceed. Prob.
Elev.
SUMMARY & RECOMMENDATIONS:
Base Flood 1%Exceed. Prob.
_
Elev.