HomeMy WebLinkAboutWPO202200040 Calculations 2022-09-21BROOKHILL STORMWATER MANAGEMENT
CALCULATIONS PACKET
(Archer Avenue Extension)
Date of Calculations
AUGUST 22, 2022
)TT R. IJNS�?-
Lic. No. 035791
t:O, 8/22/22 ,�rj
I
U.TUTIT.W-0 m-
COLLINS ENGINEERING
200 GARRETT STREET, SUITE K
CHARLOTTESVILLE, VA 22902
434.293.3719 PH
434.293.2813 FX
www.collins-engineering.com
SCS TR-55 Calculations for Archer Avenue's Extension
Soils Mapping & Table for Archer Avenue's Extension
(Source: NRCS Web Soil Survey Online Database)
Albemarle County, Virginia (VA003)
Map Unit
sy.b.1
Map Unit Name
Percent of
A01
27B
Elioak loam, 2
21.3%
to 7 percent
slopes
27C
Elioak loam, 7
31.0%
to 15 percent
slopes
34C
Glenelg loam,
15.9%
7 to 15
percent slopes
34D
Glenelg loam,
2.2%
15 to 25
percent slopes
39D
Hazel loam, 15
29.7%
to 25 percent
slopes
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)
C,
�141
AShW11d,9/ka ch'try
enswood
Of
Z
r d'
2C.
io tt
POINT PRECIPITATION FREQUENCY (PF) ESTIMATES
WITH 90% CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION
NOAA Atlas 14, Volume 2, Version 3
I PDS-based precipitation frequency estimates with 90% confidence inteivals (in inches)"
FEiziAmap
rm� �wal (Yeaw
F-EF�3;0;07F
362 463 547 6 �727 7 9 897
9 7) 1 C325-408) 11 (414-5,20) 11 K88-614) 11 (51S-751) 11 (6164,69) 11 (7,83-9.99)
U.S. Department of Agriculture
Natural Resources Conservation Service
Project: Brookhill
Location: Archer Ave. Extension
Check One: Present X
1. Runoff curve Number (CN)
Developed
TR 55 Worksheet 2: Runoff Curve Number and Runoff
Designed By: FGM, PE
Checked By: SRC, PE
FL-ENG-21A
06/04
Date: 8/22/2022
Date: 8/22/2022
Cover description
Chl (weighted) -
Drainage Area
Soil name and hydrologic
(Cover type, treatment, and hydrologic condition; percent
CN
Area
Product of CN x
total produc
Calculated 'S'
Description
group (Appendix A)
impervious; unconnected/ connected impervious area ratio)
(Acres)
Area
totalarea
Value
Impervious Areas
98
0.00
0.0
DA 4A
(Pre-Dev.)
B
Lawns in Good Condition
61
0.07
4.3
56
7.99
Woods in Good Condition
55
0.63
34.7
DA413
Impervious Areas
98
0.11
10.9
(Pre-Dev.)
B
Lawns in Good Condition
61
0.25
15.3
60
6.78
Woods in Good Condition
55
1.00
55.0
1
Impervious Areas
98
0.59
58.0
DA 4A
(Post-Dev.)
B
Lawns in Good Condition
61
0.11
6.6
92
0.83
Woods in Good Condition
55
0.00
0.0
Impervious Areas
98
0.59
57.7
DA4B
B
Lawns in Good Condition
61
0.77
47.0
77
2.98
(Post-Dev.)
Woods in Good Condition
55
0100
010
2. Runoff
I -Year Storm
2-Year Storm
10-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
0.21
0.41
1.26
DA 4A (Pre-Dev)
Runoff, Q- inches
0.32
0.57
1.55
DA 4B (Pre-Dev.)
Runoff, Q- inches
2.19
2.78
4.58
DA 4A (Post-Dev.)
Runoff, Q- inches
1.07
1.52
3.02
DA 4B (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: -�rcher Ave. Extension
Check One: Present X Developed X
Check One: Tc X T,
Segment ID:
Sheet Flow: (Applicable to T. only)
I Surface description (Table 3-1)
2 Manning's roughness coeff., n (Table 3-1
3 Flow length, L (total L < 100) (fit)
4 Two-year 24-hour rainfall, P, (in.)
5 Land slope, s (ft/ft)
6 Compute T, = [0.007(n-L)"] / P2" s 04
Designed By: FGM, PE
Checked By: SRC, PE
Through subarea n/a
FL-ENG-21A
06/04
Date; 8/22/2022
Date: 8/22/2022
DA4A.)
(Pre-Dev
re-Dev
� (PDA4B.)
ost-Dev
� (PDA4A .)
� (PDA4B
ost-Dev.)
Woods (Light
Woods (Light
Dense
Dense
Underbrush)
Underbrush)
Grass
Grass
0.4
0.4
0.24
0.24
100
100
35
90
3.62
3.62
3.62
3.62
0.23
0.13
0.46
0.09
0.13
0.16
0.03
0.11
Shallow Concentrated Flow:
7 Surface description (paved or unpaved)
Unpaved
Unpaved
8 Flow Length, L (ft)
75
65
9 Watercourse slope, s (fit/ft)
0.15
0.17
10 Average velocity, V (Figure 3-1) (ft/s)
6.3
6.8
11 Tt = L / 3600*V
0.00
0.00
Channel Flow:
12 Cross sectional flow area, a (ft)
13 Wetted perimeter, Pw (ft)
14 Hydraulic radius, r = a/P� (fit)
15 Channel Slope, s (ft/ft)
16 Manning's Roughness Coeff, n
17 V= [ 1.49r2/s" ] / n
18 Flow length, L (ft)
19 Tt= 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.
0
0
0
+
Q-) 4-1
M
�u E
ct:
M
0
0
zn
0.00
0.07
0.01
1 0.13 1 0.16 1 0.10 1 0.12 1 1
U.S. Department of Agriculture
Natural Resources Conservation Service
TR 55 Worksheet 4: Graphical Peak Discharge Method
Project; Brookhill Designed By: FGM, PE
Location; Archer Ave. Extension Checked By: SRC, PE
Check One;
Present X Developed X
Date; 8/22/2022
Date; 8/22/2022
1. Data
Drainage Area Description
Drainage Area Description
Drainage Area Description
Drainage Area Description
DA 4A
(Pre-Dev.)
DA 4B
(Pre-Dev.)
DA 4A
(Post-Dev.)
DA4B
(Post-Dev.)
Drainage Area (Am) in miles'
O.D011
0.0021
O.D011
0.0021
Runoff curve number CN=
56
60
92
77
Time of concentration (Tc)=
0.13
0.16
0.10
0.12
Rainfall distribution type=
I I I
I I I
I I I
1 11
Pond and swamp areas spread
throughout the watershed=
2. Frequency -years
1
2
10
1
2
10
1 2 10
1
2
10
3. Rainfall, P (24 hour)- inches
3.00
3.62
5.47
3.00
3.62
5.47
3.00 3.62 5.47
3.00
3.62
5.47
4. Initial Abstraction, la- inches
1.60
1.60
1.60
1.36
1.36
1.36
0.17 0.17 0.17
0.60
0.60
0.60
5. Compute la/P
0.53
0.44
0.29
0.45
0.37
0.25
0.06 0.05 0.03
0.20
0.16
0.11
6. Unit peak discharge, Qu- csm/in
425
650
975
550
675
800
Out of Range
925
925
950
7. Runoff, Q from Worksheet 2- inches
0.21
0.41
1.26
0.32
0.57
1.55
2.19 2.78 4.58
1.07
1.52
3.02
8. Pond and Swamp adjustment factor, Fp
1
1
1
1
1
1
1 1 1
1
1
1
9. Peak Discharge, Qp- cis
where Qp=Qu Am Q Fp
See SCS Unit Hydrographs
(Worksheet 5b)
See SCS Unit Hydrographs
(Worksheet 5b)
See SCS Unit Hydrographs
(Worksheet 5b)
See Detention
Basin Routings
WATERSHED SUMMARY FOR SUBAREA 4A
Area,
1-year Flow,
2-year Flow,
10-year Flow,
CN
I ac.
ds
cfs
ds
DA 4A (Pre-Dev.)
56 0.70
0.12
0.24
DA 4A (Post-Dev.)
92 0.70
2.42
3.07
0,2i
WATERSHED SUMMARY FOR SUBAREA 4B
0TV-1
CN Area,
ac.
60 1.36
77 1.36
1-year Flow, 2-year Flow, 10-year Flow,
cfs cfs cis
9 VAC 25-870-66 Channel & Flood Protection Analysis
9 VAC 25-870-66 (Point of Analysis #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 IBA: 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 postclevelopment peak flow
rate from the two-year 24-hour storm event without causing erosion of the system."
NOTE:
The two-year 24-hour storm event is not erosive in the manmade storm sewer & riprap lined
outlet protection.
Section B.4 Limits of Analysis
I.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;"
NOTE:
Contributing Drainage Area (DA 4A) 0.70 ac.
Overall Drainage Area (to Culvert) = 79.20 ac.
(See Road Plan Sheet 11 for Culvert Drainage Area Map)
Percent of Contributing DA to Overall DA = 0.9 %
9 VAC 25-870-66 (Point of Analysis #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.a:
The point of discharge (i.e. the storm sewer), "confines the postclevelopment peak flow rate
from the 10-year 24-hour storm event within the stormwater conveyance system to avoid
the localized flooding."
NOTE:
The proposed storm sewer's 10-year HGL does not overtop the inlets and is therefore
considered to be contained within the system. See Road Plan sheet 10 for HGL computations.
Section C.3.a Limits of Analysis
The flood protection analysis terminates at the site outfall because this is where the "site's
contributing drainage area is less than or equal to 1.0% of the total watershed area draining
to a point of analysis in the downstream stormwater conveyance system"
9 VAC 25-870-66 (Point of Analysis #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 BA: 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.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 :S 1. F. * (Q Pre -Developed * RV Pre -Developed ) / 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
< 0.09 cfs
Section B.4 Limits of Analysis
0.37 cfs
(From Worksheet 4 Watershed Summary)
60
(From Worksheet 4 Watershed Summary)
6.78
(From SCS TR-55 eq. 2-4)
0.32 in.
(From SCS TR-55 eq. 2-3)
77
(From Worksheet 4 Watershed Summary)
2.98
(From SCS TR-55 eq. 2-4)
1.07 in.
(From SCS TR-55 eq. 2-3)
0.80
(Factor of Safety)
0.09 cfs
The analysis terminates at the onsite subarea since subsection B.3.a is met.
9 VAC 25-870-66 (Point of Analysis #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.b.:
The point of discharge (the site outfall), "releases a postclevelopment peak flow rate for the
10-year 24-hour storm event that is less than the preclevelopment 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 4B Peak Flow Rate = 3.09 cfs
10-Year, 24-Hour Post -Development Subarea 4B Peak Flow Rate = 2.79 cfs
Section C.3 Limits of Analysis
The flood protection analysis terminates at the subarea since subsection C.2.b is met.
SCS TR-55 Hydrographs
Worksheet Sb (Modified for Clarity): Basic watershed Data
I-yr. 24-hr. SCSTR-55 Method Unit Hydrograph for the la/P &Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (Mi2 -in)
DA 4A (Pre-Dev.) 0.13 0.13 0.53 0.0002
Hydrograph Time 1-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.00
12.0
0.02
12.1
0.12
12.2
0.09
12.3
0.04
12.4
0.04
12.5
0.04
12.6
0.03
12.7
0.03
12.8
0.02
13.0
0.02
13.2
0.02
13.4
0.02
13.6
0.02
13.8
0.02
14.0
0.02
14.3
0.01
14.6
0.01
15.0
0.01
15.5
0.01
16.0
0.01
16.5
0.01
17.0
0.01
17.5
0.01
18.0
0.01
19.0
0.01
20.0
0.01
22.0
0.01
26.0
0.00
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
0.0
-0.02
SCS TR-55 Pre -Development Unit
Hydrograph (DA 4A)
5.0 10.0 15.0 20.0 25.0 30.0
Worksheet Sb (Modified for Clarity): Basic watershed Data
2-yr. 24-hr. SCSTR-55 Method Unit Hydrograph for the la/P &Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (Mi2 -in)
DA 4A (Pre-Dev.) 0.13 0.13 0.44 0.0004
Hydrograph Time 2-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.00
12.0
0.03
12.1
0.24
12.2
0.17
12.3
0.09
12.4
0.08
12.5
0.07
12.6
0.06
12.7
0.05
12.8
0.05
13.0
0.04
13.2
0.04
13.4
0.04
13.6
0.03
13.8
0.03
14.0
0.03
14.3
0.03
14.6
0.03
15.0
0.03
15.5
0.02
16.0
0.02
16.5
0.02
17.0
0.02
17.5
0.02
18.0
0.02
19.0
0.02
20.0
0.01
22.0
0.01
26.0
0.00
0.30
0�25
0.20
0.15
0.10
0.05
000
0.0
SCS TR-55 Pre -Development Unit
Hydrograph (DA 4A)
5.0 10.0 15,0 20.0 25 0 300
Worksheet 5b (Modified for Clarity): Basic watershed Data
10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (Mi2 -in)
DA 4A (Pre-Dev.) 0.13 0.13 0.29 0.0014
Hydrograph Time 10-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.21
12.0
0.79
12.1
1.29
12.2
0.72
12.3
0.30
12.4
0.24
12.5
0.21
12.6
0.17
12.7
0.15
12.8
0.13
13.0
0.12
13.2
0.11
13.4
0.10
13.6
0.09
13.8
0.08
14.0
0.07
14.3
0.07
14.6
0.06
15.0
0.06
15.5
0.05
16.0
0.05
16.5
0.04
17.0
0.04
17.5
0.04
18.0
0.04
19.0
0.03
20.0
0.03
22.0
0.03
26.0
0.00
1.40
1.20
1.00
0.80
0.60
0.40
0.20
000
0.0
SCS TR-55 Pre -Development Unit
Hydrograph (DA 4A)
5.0 10.0 15.0 20.0 25�O 30.0
Worksheet Sb (Modified for Clarity): Basic watershed Data
I-yr. 24-hr. SCSTR-55 Method Unit Hydrograph for the la/P &Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (Mj2 -in)
DA 4B (Pre-Dev.) 0.16 0.16 0.45 0.0007
Hydrograph Time 1-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.00
12.0
0.05
12.1
0.37
12.2
0.26
12.3
0.13
12.4
0.12
12.5
0.11
12.6
0.09
12.7
0.08
12.8
0.07
13.0
0.07
13.2
0.06
13.4
0.06
13.6
0.05
13.8
0.05
14.0
0.05
14.3
0.04
14.6
0.04
15.0
0.04
15.5
0.03
16.0
0.03
16.5
0.03
17.0
0.03
17.5
0.03
18.0
0.03
19.0
0.02
20.0
0.02
22.0
0.02
26.0
0.00
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
000
0.0
SCS TR-55 Pre -Development Unit
Hydrograph (DA 413)
5.0 10.0 15.0 20.0 25�O 30.0
Worksheet Sb (Modified for Clarity): Basic watershed Data
2-yr. 24-hr. SCSTR-55 Method Unit Hydrograph for the la/P &Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (Mi2 -in)
DA 4B (Pre-Dev.) 0.16 0.16 0.37 0.0012
Hydrograph Time 2-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.19
12.0
0.68
12.1
1.13
12.2
0.63
12.3
0.26
12.4
0.21
12.5
0.18
12.6
0.15
12.7
0.13
12.8
0.12
13.0
0.10
13.2
0.09
13.4
0.08
13.6
0.08
13.8
0.07
14.0
0.06
14.3
0.06
14.6
0.06
15.0
0.05
15.5
0.05
16.0
0.04
16.5
0.04
17.0
0.04
17.5
0.03
18.0
0.03
19.0
0.03
20.0
0.02
22.0
0.02
26.0
0.00
1.20
1.00
0.80
0.60
0.40
0.20
000
0.0
SCS TR-55 Pre -Development Unit
Hydrograph (DA 413)
5�O 10.0 15A) 20.0 25.0 30.0
Worksheet 5b (Modified for Clarity): Basic watershed Data
10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (Mi2 -in)
DA 4B (Pre-Dev.) 0.16 0.16 0.25 0.0033
Hydrograph Time 10-yr Discharges
(hrs.)
WS)
0.0
0.00
11.0
0.00
11.3
0.00
11.6
0.00
11.9
0.51
12.0
1.88
12.1
3.09
12.2
1.73
12.3
0.72
12.4
0.57
12.5
0.49
12.6
0.42
12.7
0.35
12.8
0.32
13.0
0.28
13.2
0.25
13.4
0.23
13.6
0.21
13.8
0.19
14.0
0.18
14.3
0.16
14.6
0.15
15.0
0.14
15.5
0.13
16.0
0.11
16.5
0.10
17.0
0.10
17.5
0.09
18.0
0.09
19.0
0.08
20.0
0.07
22.0
0.06
26.0
0.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
SCS TR-55 Pre -Development Unit
Hydrograph (DA 413)
5.0 MO 15.0 20.0 25.0 30.0
Worksheet 5b (Modified for Clarity): Basic watershed Data
I-yr. 24-hr. SCSTR-55 Method Unit Hydrograph for the la/P &Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (Mi2 -in)
DA 4A (Post-Dev.) 0.10 0.10 0.06 0.0024
Hydrograph Time 1-yr Discharges
(hrs.)
WS)
0.0
0.00
11.0
0.06
11.3
0.08
11.6
0.13
11.9
0.80
12.0
1.55
12.1
2.42
12.2
1.49
12.3
0.52
12.4
0.35
12.5
0.29
12.6
0.25
12.7
0.21
12.8
0.18
13.0
0.16
13.2
0.14
13.4
0.12
13.6
0.11
13.8
0.10
14.0
0.09
14.3
0.08
14.6
0.08
15.0
0.07
15.5
0.06
16.0
0.06
16.5
0.05
17.0
0.05
17.5
0.05
18.0
0.04
19.0
0.04
20.0
0.03
22.0
0.03
26.0
0.00
SCS TR-55 Post -Development Unit
Hydrograph (DA 4A)
100
2.50
2.00
1.50
1.00
0.50
0.00
0.0
5.0
10.0
15.0
20.0
25.0
30.0
Worksheet Sb (Modified for Clarity): Basic watershed Data
2-yr. 24-hr. SCSTR-55 Method Unit Hydrograph for the la/P &Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (Mi2 -in)
DA 4A (Post-Dev.) 0.10 0.10 0.05 0.0030
Hydrograph Time 2-yr Discharges
(hrs.)
WS)
0.0
0.00
11.0
0.07
11.3
0.10
11.6
0.16
11.9
1.02
12.0
1.97
12.1
3.07
12.2
1.90
12.3
0.66
12.4
0.45
12.5
0.37
12.6
0.32
12.7
0.26
12.8
0.23
13.0
0.20
13.2
0.17
13.4
0.16
13.6
0.14
13.8
0.13
14.0
0.12
14.3
0.10
14.6
0.10
15.0
0.09
15.5
0.08
16.0
0.07
16.5
0.06
17.0
0.06
17.5
0.06
18.0
0.05
19.0
0.05
20.0
0.04
22.0
0.04
26.0
0.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
000
0.0
SCS TR-55 Post- Deve lopme nt Unit
Hydrograph (DA 4A)
5.0 10.0 15 0 20.0 25.0 30 0
Worksheet 5b (Modified for Clarity): Basic watershed Data
10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below
Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (Mi2 -in)
DA 4A (Post-Dev.) 0.10 0.10 0.03 0.0050
Hydrograph Time 10-yr Discharges
(hrs.)
(cfs)
0.0
0.00
11.0
0.12
11.3
0.17
11.6
0.27
11.9
1.67
12.0
3.24
12.1
5.06
12.2
3.12
12.3
1.09
12.4
0.74
12.5
0.62
12.6
0.52
12.7
0.43
12.8
0.38
13.0
0.33
13.2
0.29
13.4
0.26
13.6
0.23
13.8
0.21
14.0
0.19
14.3
0.17
14.6
0.16
15.0
0.15
15.5
0.13
16.0
0.12
16.5
0.11
17.0
0.10
17.5
0.10
18.0
0.09
19.0
0.08
20.0
0.07
22.0
0.06
26.0
0.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
SCS TR-55 Post -Development Unit
Hydrograph (DA 4A)
0.0 5.0 10.0 15.0 20.0 25.0
30.0
Detention Basin 4 Routing Calculations
Level Spreader 4 Calculations
Archer Avenue Extension- Detention Basin 4
BasinFlow printout
INPUT:
Basin: Archer Avenue Extension- Detention Basin 4
6 Contour Areas
Elevation(ft)
436.00
438.00
440.00
442.00
444.00
446.00
Start—Elevation(ft)
6 Outlet Structures
Outlet structure 0
Orifice
Area(sf) Computed Vol.(cy)
137.00
0.0
392.00
18.8
738.00
60.0
1293.00
134.2
1925.00
252.6
2665.00
421.9
436.00 Vol.(cy) 0.00
name: Barrel- Str. Al
area (sf)
3.142
diameter or depth (in)
24.000
width for rect. (in)
0.000
coefficient
0.500
invert (ft)
432.000
multiple
I
discharge out
of riser
Outlet structure 1
Orifice
name: Barrel- Str. AS
area (sf)
0.196
diameter or depth (in)
6.000
width for rect. (in)
0.000
coefficient
0.500
invert (ft)
430.000
multiple
I
discharge out
of riser
Outlet structure 2
Orifice
name: Low -Flow Orifice
area (sf) 0.010
diameter or depth (in) 1.330
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 436.000
multiple I
discharge into riser
Page I
Archer Avenue Extension- Detention Basin 4
Outlet structure 3
Orifice
name: Mid -Flow Orifice
area (sf) 0.545
diameter or depth (in) 10.000
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 441.150
multiple I
discharge into riser
Outlet structure 4
Weir
name:
diameter (in)
side angle
coefficient
invert (ft)
multiple
discharge
transition at (ft)
orifice coef.
orifice area (sf)
Outlet structure 5
Weir
name:
length (ft)
side angle
coefficient
invert (ft)
multiple
discharge
4 Inflow Hydrographs
Hydrograph 0
SCS
Riser -
Str. A2
48.000
0.000
3.300
443.500
1
into riser
1.215
0.500
12.566
Emergency Spillway
8.000
0.000
3.300
444.500
1
through dam
name: 1-yr 24-hr TR-55 SCS Method Design Storm
Area (acres) 1.360
CN 77.000
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)
1.787
peak time
(hrs)
11.922
volume (cy)
195.663
Page 2
Hydrograph I
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 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)
Hydrograph 3
SCS
Archer Avenue Extension- Detention Basin 4
2-yr 24-hr TR-55 SCS Method Design Storm
1.360
77.000
2
3.620
0.1200
0.0200
30.000
1.00
true
2.537
11.922
277.732
10-yr 24-hr TR-55
1.360
77.000
2
5.470
0.1200
0.0200
30.000
1.00
true
5.041
11.922
551.850
name: 100-yr 24-hr TR-55
Area (acres) 1.360
CN 77.000
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)
10.299
peak time
(hrs)
11.922
volume (cy)
1127.368
SCS Method Design Storm
SCS Method Design Storm
Page 3
Archer Avenue Extension- Detention Basin 4
OUTPUT:
Routing Method: storage -indication
Hydrograph 0
Routing Summary of Peaks
inflow (cfs)
discharge (cfs)
water level (ft)
storage (cy)
Hydrograph I
Routing Summary of Peaks:
inflow (cfs)
discharge (cfs)
water level (ft)
storage (cy)
Hydrograph 2
Routing Summary of Peaks
inflow (cfs)
discharge (cfs)
water level (ft)
storage (cy)
I-yr 24-hr TR-55 SCS Method Design Storm
1.784 at 11.92 (hrs)
0.087 at 12.24 (hrs)
441.113 at 12.54 (hrs)
96.205
2-yr 24-hr TR-55 SCS Method Design Storm
2.533 at 11.92 (hrs)
1.036 at 12.08 (hrs)
441.688 at 12.08 (hrs)
119.859
10-yr 24-hr TR-55 SCS Method Design Storm
5.033 at 11.92 (hrs)
2.785 at 12.06 (hrs)
443.070 at 12.06 (hrs)
191.770
Hydrograph 3
Routing Summary of
Peaks: 100-yr
24-hr TR-55
SCS Method Design Storm
inflow (cfs)
10.281
at 11.92
(hrs)
discharge (cfs)
9.819
at 11.94
(hrs)
water level (ft)
443.789
at 11.94
(hrs)
storage (cy)
237.902
Mon Sep 12 10:17:13 EDT 2022
Page 4
LEVEL SPREADER 4 DESIGN
Per VSMH Chpt. 11, Section 11.5.3:
Step 1 Area =
(Eqn 11.11) TV =
Q.=
(From Worksheet 2) CN =
1.36 ac.
2,594 cf
0.53 watershed inches
77
Step 2 Tc =
0.12 hrs
Step 3 la =
0.60
la / P =
0.60
q,=
350 csm/in
A =
0.002 mi'
q pT, =
0.4 cfs
NOTES:
q PTvis the Treatment Volume peak discharge, or the peakflow rate for the 1-inch rainfall event.
The level spreader receives this Treatment Volume runoff via a separate pipe outfall.
Per the VA DEQ Specification #2, page 14, the Level Spreader should be designed per the following:
"13 feet of Level Spreader length per every 1 cubic foot per second (cfs) of inflow for discharges to a Vegetated Filter
Strip or Conserved Open Space consisting of native grasses or thick ground cover."
The proposed vegetated filter strip located below subarea 4B's'Detention Basin 413' will predominantly consist of native
grasses and will have a thick ground cover. Therefore a 13' per 1 cfs design is applicable to'Level Spreader 413'.
Site Specific LS length -to -Flow Ratio = 13 ft per I cfs
Min. Level Spreader 4 Design Length= 5 ft
Notes:
Max. LS Length 130 ft
Min. LS Length 13 ft
Proposed LS Length = 13 ft
Worksheet for Str. A5 Treatment Volume Capacity Check
Project Description
Friction Method
Manning
Formula
Solve For
Normal Depth
Input Data
Roughness Coefficient
0.010
Channel Slope
0.037 ft/ft
Diameter
6.0 in
Discharge
0.40 cis
Results
Normal Depth
2.2 in
Flow Area
0.1 ft2
Wetted Perimeter
0.6 ft
Hydraulic Radius
1.2 in
Top Width
0.48 ft
Critical Depth
3.9 in
Percent Full
36.5%
Critical Slope
0.005 ft/ft
Velocity
6.17 ft/s
Velocity Head
0.59 ft
Specific Energy
0.77 ft
Froude Number
2.967
Maximum Discharge
1.51 cis
Discharge Full
1.40 cis
Slope Full
0.003 ft/ft
Flow Type
Supercritical
GVF Input Data
Downstream Depth
0.0 in
Length
0.0 ft
Number Of Steps
0
GVF Output Data
Upstream Depth
0.0 in
Profile Description
N/A
Profile Headloss
0.00 ft
Average End Depth Over Rise
0.0%
Normal Depth Over Rise
36.5%
Downstream Velocity
Infinity ft/s
Upstream Velocity
Infinity ft/s
Normal Depth
2.2 in
Critical Depth
3.9 in
Channel Slope
0.037 ft/ft
Critical Slope
0.005 ft/ft
Bentley Systems, Inc. Haestad Methods Solution FlowMaster
Detention Basin 4- Barrel TW Analysis.fmB Center [10.03.00.031
9/1212022 27 Slernon Company Dnw Suite 200 W Page 1 of 1
Watertown, CT 06795 USA +1-203-755-16N
Riprap Outlet Protection Calculations
Structure Al's Tailwater Analysis
crs O�Cccz tA-JQ, �O-yx %Uszll.�)
Cl-IS ( r2KCGCOI =-Yr,
?C? L6
Ak
OV, > wa�l.$)
\—P\ = VA' , 1p�- \'� I wj�-- � I I I
\Joo,v cl., kt ��C,4c izy--)?Tg \2:
Cn
0
DESIGN OF OUTLET PROTECTION FROM A ROUND PIPE FLOWING FULL
MINIMUM TAILWATER CONDITION (Tw � 0.5 DIAMETER)
Outlet I - Do + La
Pipe T- 2 mj.-j
D
Do
ot:::2ql
Diamete 1
La
Tallwate.r- O,5Do
ok
veoe 50
1 0111
Recomended Mi,.
4
3
2
I � 1 1 1 !';1 � I I: !I; 111ij , 0
3 5 10 20 50 3 100 200 500 1000
Discharqe, ft./sec.
Q (j ESIGN
1992
RAV
PIPE OUTLET CONDITIONS
A A
'IPE OUTLET TO FIAT
REA WITH NO DEFINED
.HANNEL
LL a
0 %
d
7-
SECTION A -A FILTER CLOTH KEY IN 6'-g"; RECOMMENDED FOR ENTIRE PERIMETER
f
3do (MIN.)
IIPE OUTLET TO WELL
IEFINED CHANNEL
I
d
SECTION A -A I T r
FILTER CLOTH KEY IN 6"-Y'; 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 6 INCHES.
Source: Va. DSWC
Plate 3.18-1
111-157
Worksheet for Str. Al Tailwater Analysis
Project Description
Friction Method
Manning
Formula
Solve For
Normal Depth
Input Data
Roughness Coefficient
0.010
Channel Slope
0.115 ft/ft
Diameter
24.0 in
Discharge
9.82 cis
Results
Normal Depth
5.1 in
Flow Area
0.5 ft2
Wetted Perimeter
1.9 ft
Hydraulic Radius
3.0 in
Top Width
1.64 ft
Critical Depth
13.5 in
Percent Full
21.2%
Critical Slope
0.003 ft/ft
Velocity
20.18 ft/s
Velocity Head
6.33 ft
Specific Energy
6.75 ft
Froude Number
6.522
Maximum Discharge
107.09 cis
Discharge Full
99.55 cis
Slope Full
0.001 ft/ft
Flow Type
Supercritical
GVF Input Data
Downstream Depth
0.0 in
Length
0.0 ft
Number Of Steps
0
GVF Output Data
Upstream Depth
0.0 in
Profile Description
N/A
Profile Headloss
0.00 ft
Average End Depth Over Rise
0.0%
Normal Depth Over Rise
21.2%
Downstream Velocity
Infinity ft/s
Upstream Velocity
Infinity ft/s
Normal Depth
5.1 in
Critical Depth
13.5 in
Channel Slope
0.115 ft/ft
Critical Slope
0.003 ft/ft
Bentley Systems, Inc. Haestad Methods Solution FlowMaster
Detention Basin 4- Barrel TW Analysis.fmB Center [10.03.00.031
9/1212022 27 Slernon Company Dnw Suite 200 W Page 1 of 1
Watertown, CT 06795 USA +1-203-755-16N
Virginia Runoff Reduction Method
Water Quality Calculations
- Verw.3A
2�1 BMP R11,111d, ad *�Willftlll
I�I�AftfrerAwaaueEd�W
.a.: I 8122/M2
BW ra—ar, SpffIft-111, bv: 20 13 D raft Std s & S pecs
te information
Post -Development Project (Treatment Volume and Loads)
uad� (.)
241
dl 11 Mh,r tIlf W b, ra—diml—ld
2�47
ra,� C� wa�
.97
O�17
Conaftarts
R. -ff Ccafffician. (Mr)
A- al R,inall (har,,�
A�h
Wh
",,. r.r., ..ra
TIM Ph��rlrla �) EMC (160
M—g"
_r'
U.",
'. .'a,' �) .0 (�
11. r— 1—
.,,I
�r�TP �d IIWWMMJ
A�
P, —. I—Ir)
%F,a-t
al,aTuft�r( ....
(tar, 020
Dml� �� 3
DM�� A *14
A-'! ...1 1..! —.1 —1-
-M M
--el
.-m
M,.., .d.Al
7=77
�1:
I
I
I
I
I
I
I
I
I
1
1
1
1
1
1
1
1
1
1.
1771-777:
7 ... .......
7l--mm7l--
I
-EF EBI
TIS...-ABB.FBA A, ==K
F
BAE-FESUFTEDEEFEASTA, : ......
SEEEAAFEB.�.....EFF.....
l"-`:.-,:E-sw ]=A �K S OX
"F I BIBB
I--F K-El - 1-111-47.1
-I.-Ill-FE-PON-EVIDEE.-IM
. . I. . IF A . .
AM WALITY CWPDANCE TAB FOR SITE C�PIJA� CALSMATIBBIES
I BF-
FA-
Site Results (Water Quality Compliance)
Area Checks
IMPERVIOUS COVER
IMPERVIOUS COVER TREATED
MANAGED TURF AREA TREATED
Site Treatment Volume (ft')
Runoff Reduction Volume and TP Bv Drainage Area
TP LOAD REDUCTION ACHIEVED (Ib/yr)
NITROGEN LOAD
Total
AREA CHECK
000
00,
000
000
0.00
OK.
0 DO
02
000
000
O.DO
OK.
0 DO
0.59
0 DO
uxad
000
O.DO
OK.
000
077
000
000
0.00
OLOOM
Ot
000
000
0.00
1,297 0 0
1.63 O.DO 0.00
0.81 0.00 0.00
0.81
0.82 0.00
0.82
I REMAININGTP LOADREDUCTION REQUIRED (lb/vr):l 1.00 1 1 1 1 1 1 1
Total Nitrogen (For Information
2 1 it �X�i 4 3111-111 -IIJ 4 -111,q ir-1 ffl.,N I I I iTi 4 -XI I 7AMI I I
I I I
Runoff Volume and Cum Number Calculations
F ------ T_
Enter design sWm rainfall depths (in):
!=�,rrff
� ��,,,-Svppffp
t�r7pdd
Its, ARSAA dr, t�
.1hotea (see Below):
11] "e come numbers and mnoff valumes atureparded! in this spreadribrat her each promote area are limited in their applectilah"r damearminning and demonstration, compliance with water connote,
Sed suffis U,,r', Sold, and Documentation let isfiflumnalseformandan,
(21 Runoff Volume (W) for pri and postdrivelopment drainage ancons must be in witurnarand ones (a,, mrficat or cubic feet) when usion, the Ener, Balance Equator. Runoff measured in wasserthad
berwo and shown in me spreadsheet as RV(watershed inch) can only he used in the EneW Balance Equaradmin when the pre and �tAe�bpme�dminapa�samequal.�he�iwRV(watershedl�
in�)mu��multipliMbythedminageama.
(31 Adjusted! Cals are based on runoff abortion volumes as calculated in D.A. tabs. An afterrame, CN adjustment caidulation for carpenter! Bonds is included in OMP speofficadvain No. 5.
der,meencente,
777-
i
Dralral Area Cum Numbers and Runoff Depths-
Offare numbers (CN, Mal and irshrojilifalepths (RV OW Caffinjouted With and anithourtinedpardiffin Prattices.
DrairoW area A
A soup
Bjsoils
C Soils
D sells
AmAI ),I!
—
.—t/OWn Space — undisturbed, R=
fordo/open space or advocated
Pi�N
30
no
Sat
rcour
70
ucoo
77
.1
va, am ') n :
1B.I.M. (ft
—
�n.g�luff—d.,t.�M,�dMIoryam,,rot�er
trurfrobeencounced/managed!
Adea�,Nwcpaau
Roo
3N
ou"
lit
up"
74
ow
1.
Mi
N
OW
S.
OW
S.
"T
98
It
CNR.A.Al
0
1,Rcar storm
RVeassai with, no Flumadfif Red n:�
WeadvaNsaw f�) with Fambeff Red
_0:-T
No
Phates, plation,
DrainaV Area 8
A Salihs
B Soils
C ScAla
0 sails
Forest/iSpen Space — undsturbed, protected
doestionan space orrefore,ledland
Anew (no—)
CN
ROO
3.
Rod
11
Rod
77
Managrallurf—dralubbed aded lot ards or other
turf art be moscretimadaMeal
(mara)
CN
ond
39
61
Bit
as,
0.00
impervanis Imber
Aram hascres)
�N
0.00
SA
--- ---T—
. So
S.
. M
as
O.So
S.
CNI.A. .1
77
1,pear storm 2,pear aboard 10-year storm
with no Flumayff Relludion *
RVR_vN,w (Randularrimcf-inch) AM A. —.ffRWudi.n*
I zusted! Me
Ell
Sff�
1 73
1 74
'See Notes above
�inuige Areas C
A Sells
B Soils
C Soils
D Sells
Tonal Men James): 0.00
dro,'10,bers Space - undisturbed, protecte
forest/open space or raboreard lad
creslocres)
S
O�ffl
30
SS
d.
si�dp
77
Runoff RIdamon
sablume, (ail 0
liturrigial turf - denumed, anced lot Yards or ot�cr
turf W be menved/marrogeal
Area (,,re,)
C N
gc� d
0..
3N
.1
r..
7,1
0..
.0
in,croup., venear
A,ea .,,a,,,
0�00
S.
aran
d..
S.
Ou.
1-,,abar storm
2-"ar actionsin
10,,dur room
RVa,ven,and (abableachouPpol iscith .. Runcifif Reduction
aw
O.w
O.w
wifth Runoff Reduction*
acon
O.S.
------- FM-ju.�CN-
SSee Notes above
�irba,,e Mass 0
A Sells
B Soils
C Soils
0 Sells
Todal Are. (arres)i D.W
Foicabben Spere- undisturbed, reported
farrala.pa. a,_ at barricaded land
Area (ances)
IN
0..
30
0.00
55
70
0..
77
Ramon shounducar
voluen. Mk 0
Worried] �rf - disturbed, Moral for pHs or offiner
trairfor be nabounced/maniMpal
licess (arms)
IN
0..
3N
61
74
Ourn
so
imparpospes (probir
Non bacres)
IN
0..
99
S.
0..
99
MID -au 0)
1,ear storm
2plabi
164ear storm
RVicervion,and unto no Rancraff ounduccurn -
ow
am
Wapinusea, f�) ufflia Rustruff Reduelsom -
am
bond
0
0
a
"Sor, Notes boadde,
Draino, flader E
A Sells
R !iails
C Soils
D Sells
TocalAreabacres): 0.00
'o—VOWn Space - undisturbed, pratubmal
foreartiopern spre or remained land
Areas (acres)
IN
0..
3D
am
11
0
7.
Ound
77
Runoff Reduction
arriparce ft�, 0
na,Mlff-diqu�d,��dMrWMsor&her
arl W be monabodifinpuroi
— bacres)
IN
39
61
74
0..
10
Impressions (svirer
licess (arms)
IN
am
ad
ad
0..
S.
_ or & a
Micus. a
0
1-year storm
2-Vear storm
10,ban storm
Woudau,,ad foarturafted-fri with no In nuff Woodrum
0..
a..
M
saffh Ri noff Reduction"
am
dkDD—
oidjobstani M.
4be Nualin, calendar
0
0