HomeMy WebLinkAboutWPO201900038 Calculations 2020-09-28MARTHA JEFFERSON HOSPITAL- PARKING LOT EXPANSION
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Date of Calculations
JUNE 13, 2019
Revised
SEPTEMBER 6, 2020
PREPARED BY:
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
Soils Mapping (Source: NRCS Web Soil Survey Online Database)
Soils Table (Source: NRCS Web Soil Survey Online Database)
Albemarle County, Virginia (VA003)
Albemarle County, Virginia (VA003)
Map Unit Map Unit Name percent of
Symbol AOI
72C3 Rabun clay, 7 to 100.0%
15 percent
slopes, severely
eroded
Totals for Area of 100.0%
Interest
Note: The soils' properties witin this development are predominantly composed of hydrologic group
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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POINT PRECIPITATION FREQUENCY (PF) ESTIMATES
WITH 90%CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION
NOAA Atlas 14, Volume 2, Version 3
PDSbased precipitation frequency estimates with 90% confidence In ervals (in inches)'
Aywage rscurt m iWmW (years
Ouraan° O1 O2 OS f0 Ol�
10D ®® 102
FT,(23 7239) (326d511) (4.18-524) 1493.6.19) (6. 2-1958) 11
(64-8 .9.18) 11 (1. 3--10.1) 11 (899-115)
U.S. Department of Agriculture
Natural Resources Conservation Service
FL-ENG-23A
06/04
TR 55 Worksheet 2: Runoff Curve Number and Runoff
Project: Martha Jefferson Hospital Parking Lot Designed By: FGM, PE Date: 6/13/2019
Location: Peter Jefferson Parkway Checked By: SRC, PE Date: 6/13/2019
Check One: Present X Developed
1. Runoff curve Number (ON)
Cover description
ON (weighted) _
Drainage Area
Soil name hydrologic
Area
Produ CN
Calcualued'S'
(Cover type, treatment, and hydrologic condition; percent
[N
total product/
Description
group (Appendix A)
up(Appendix
impervious;unconnected/ connected impervious area ratio)
(Acres)
Area
zArea
total area
Value
Impervious Areas
98
0.55
54.3
DAA
B
Woods in Good Condition
55
0.00
0.0
90
1.08
(Present)
Lawns in Good Condition (75%+Groundcover)
61
0.15
8.9
Impervious Areas
98
0.03
3.2
DAB
(Present)
B
Woods in Good Condition
55
0.00
0.0
63
5.89
Lawns in Good ConditionQS%+Groundcover)
61
0.60
36.4
Impervious Areas
98
0.23
22.3
DAA
B
Woods in Good Condition
55
0.00
0.0
93
0.10
(Developed)
Lawns in Good Condition (]5%+Groundcover)
61
0.03
2.0
Impervious Areas
98
0.74
72.4
DAB
(Developed)
B
Woods in Good Condition
55
0.00
0.0
87
1.56
Lawns in Good Condition (]5%+Groundcover)
61
0.33
20.2
2. Runoff
1-year Storm
1 2-year Storm
I 10-year Storm
I Drainage Area Description
Frequencyyears1
2
10
n/a
Rainfall, P(24 hour) -inches
3.02
3.G5
5.53
n/a
Runoff, Q-inches
2.03
2.61
4.42
DA A(Present)
Runoff, Q-inches
0."
0.73
1.85
DA B(Present)
Runoff, Q-inches
2.31
2.92
4.]]
DAA (Developed)
Runoff, Q-inches
1.72
2.28
4.02
DA B(Developed)
U.S. Department of Agriculture
Natural Resources Conservation Service
TR 55 Worksheet 3: Time of Concentration (T,) or Travel Time (Tr)
Project: Martha Jefferson Hospital Parking Lot
Location: Peter Jefferson Parkway
Check One: Present X Developed X
Check One: T, X Tt
Segment
Sheet Flow: (Applicable to T, only)
Designed By: FGM, PE
Checked By: SRC, PE
Through subarea n/a
DA A I DA B I DA A I DA B
FL-ENG-21A
06/04
Date: 6/13/2019
Date: 6/13/2019
1 Surface description (Table 3-1)
Dense Grass
Dense Grass
2 Manning's roughness coeff., n (Table 3-1
0.24
0.24
3 Flow length, L (total L < 100) (ft)
35
95
4 Two-year 24-hour rainfall, Pi (in.)
3.7
3.7
5 Land slope, s (ft/ft)
0.14
0.06
6 Compute T,= [0.007(n'L)°'vJ / Pis s°'`
0.04
0.13
Shallow Concentrated Flow:
7 Surface description (paved or unpaved)
8 Flow Length, L (ft)
9 Watercourse slope, s(ft/ft)
10 Average velocity, V (Figure 3-1) (ft/s)
11 Tt=L/3600'V
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's[/n
18 Flow length, L (ft)
19 Ti L/3600'V
20 Watershed or subarea Tc or T,
(Add Tt in steps 6, 11 and 19)
Note: The shortest SCS Tc is 0.10 hrs.
0.10 1 0.13 1 0.10 1 0.10
U.S. Department of Agriculture
Natural Resources Conservation Service
TR 55 Worksheet 4: Graphical Peak Discharge Method
Project: Martha Jefferson Hospital Parking Lot Designed By: FGM, PE
Location: Peter Jefferson Parkway Checked By: SRC, PE
Check One: Present X Developed X
Date: 6/13/2019
Date: 6/13/2019
1. Data
Drainage Area
Description
Drainage Area
Description
Drainage Area
Description
Drainage Area
Description
Drainage Area
Description
DA A
(Present)
DA B
(Present)
DA A
(Developed)
DA B
(Developed)
Drainage Area (Am) in miles' =
0.0011
0.0010
0.0004
0.0017
Runoff curve number CN=
90
63
93
87
Time of concentration (Tc)=
0.10
0.13
0.10
0.10
Rainfall distribution type=
II
II
II
II
Pond and swamp areas spread
throughout the watershed=
0
0
0
0
2. Frequenry-years
1
2
10
1
2
10
1
2
10
1 2 10
3. Rainfall, P (24 hour) -inches
3.02
3.65
5.53
3.02
3.65
5.53
3.02
3.65
5.53
3.02 3.65 5.53
4. Initial Abstraction, la -inches
0.22
0.22
0.22
1.18
1.18
1.18
0.14
0.14
0.14
0.31 0.31 0.31
5. Compute la/P
0.07
0.06
0.04
0.39
0.32
0.21
0.05
0.04
0.03
0.10 0.09 0.06
6. Unit peak discharge, Qu-am/in
1000
1000
1000
750
850
900
1000
1000
1000
1000 1000 1000
7. Runoff, Qfrom Worksheet 2- inches
2.03
2.61
4.42
0.44
0.73
1.85
2.31
2.92
4.77
1.72 2.28 4.02
8. Pond and Swamp adjustment factor, Fp
1
1
1
1
1
1
1
1
1
1 1 1
9. Peak Discharge, Op- cfs
where Qp=Qu Am Q Fp
2.22
2.86
4.83
0.32
0.61
1.64
0.94
1.19
1.94
Routed Through The
SWM Facility
WATERSHED SUMMARY
Pre -Development
CN
Area, ac.
1-year Flow,
2-year Flow, cis
10-year Flow,
ds
cfs
DA A(Present)
90
0.70
2.22
2.86
4.83
DA B (Present)
63
0.63
0.32
0.61
1.64
77
1.33
2.54
3.47
6.47
Post -Development
CN
Area, ac.
1-year Flow,
2-year Flow, cis
10-year Flow,
cis
cfs
DAA (Developed)
93
0.26
0.94
1.19
1.94
BasinFlow printout
INPUT:
Basin: MJH Parking Lot- Detention Cell Routings
5 Contour Areas
Elevation(ft) Area(sf) Computed Vol.(cy)
516.50 5.00 0.0
517.00 1455.00 9.5
518.00 2334.00 79.1
519.00 3323.00 183.3
520.00 4369.00 325.3
Start—Elevation(ft) 516.50 Vol.(cy)
4 Outlet Structures
Outlet structure 0
Orifice
name: Barrel
area (sf) 0.785
diameter or depth (in) 12.000
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 516.500
multiple 1
discharge out of riser
Outlet structure 1
Orifice
name: Low -Flow Orifice
area (sf) 0.049
diameter or depth (in) 3.000
width for rect. (in) 0.000
coefficient 0.500
invert (ft) 516.500
multiple 1
discharge into riser
Outlet structure 2
Weir
name: YD-1
diameter (in)
24.000
side angle
0.000
coefficient
3.300
invert (ft)
518.660
multiple
1
discharge
into riser
transition at (ft)
0.608
orifice coef.
0.500
EWE
orifice area (sf) 3.142
Outlet structure 3
Weir
name: Emergency Spillway
length (ft)
35.000
side angle
0.000
coefficient
3.300
invert (ft)
519.660
multiple
1
discharge
through dam
4 Inflow Hydrographs
Hydrograph 0
SCS
name: 1-yr.
24-hr. SCS TR-55 Design Storm
Area (acres)
1.070
CN
87.000
Type 2
rainfall, P (in)
3.020
time of conc. (hrs)
0.1000
time increment (hrs)
0.0200
time limit (hrs)
30.000
fudge factor
1.00
routed
true
peak flow (cfs)
2.385
peak time (hrs)
11.917
volume (cy)
252.511
Hydrograph 1
SCS
name: 2-yr.
24-hr. SCS TR-55 Design Storm
Area (acres)
1.070
CN
87.000
Type 2
rainfall, P (in)
3.650
time of conc. (hrs)
0.1000
time increment (hrs)
0.0200
time limit (hrs)
30.000
fudge factor
1.00
routed
true
peak flow (cfs)
3.147
peak time (hrs)
11.917
volume (cy)
333.163
Hydrograph 2
SCS
name: 10-yr. 24-hr. SCS TR-55 Design Storm
Area (acres) 1.070
CN 87.000
Type 2
rainfall,
P (in)
5.530
time of conc.
(hrs)
0.1000
time increment
(hrs)
0.0200
time limit
(hrs)
30.000
fudge
factor
1.00
routed
true
peak flow
(cfs)
5.524
peak time
(hrs)
11.917
volume (cy)
584.881
Hydrograph 3
SCS
name: 100-yr.
24-hr. SCS TR-55 Design Storm
Area (acres)
1.070
CN
87.000
Type 2
rainfall, P (in)
9.080
time of conc. (hrs)
0.1000
time increment (hrs)
0.0200
time limit (hrs)
30.000
fudge factor
1.00
routed
true
peak flow (cfs)
10.189
peak time (hrs)
11.917
volume (cy)
1078.684
OUTPUT:
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)
Peaks: 1-yr. 24-hr
2.374 at
0.249 at
518.222 at
99.130
Peaks: 2-yr. 24-hr
3.132 at
0.277 at
518.600 at
137.133
SCS TR-55 Design Storm
11.92 (hrs)
12.26 (hrs)
12.36 (hrs)
SCS TR-55 Design Storm
11.92 (hrs)
12.36 (hrs)
12.44 (hrs)
Peaks: 10-yr. 24-hr. SCS TR-55 Design Storm
5.499 at 11.92 (hrs)
4.127 at 12.02 (hrs)
518.984 at 12.02 (hrs)
storage (cy)
Hydrograph 3
Routing Summary of
inflow (cfs)
discharge (cfs)
water level (ft)
storage (cy)
181.331
Peaks: 100-yr. 24-hr. SCS
10.141 at 11.92
7.188 at 12.02
519.727 at 12.02
282.584
Sun Sep 06 08:14:14 EDT 2020
TR-55 Design Storm
(hrs)
(hrs)
(hrs)
9 VAC 25-870-66 Subareas A & B
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
"When stormwater from a development is discharged to a natural stormwater conveyance
system, the maximum peak flow rate from the one-year 24-hour storm following the land -
disturbing activity shall be calculated either..." by a. or b.
Section B.3.a.
In accordance with
the following methodology:
Q Developed !� I.F. *
(Q Pre -Developed * RV Pre -Developed) / RV Developed
Q Allowed<
1.23 cfs Where: QPre-Developed—
2.54 cfs
CN Pre -Developed—
77
S Pre -Developed—
2•93
RV Pre -Developed—
1.10 in.
CN Post -Developed—
88
S Post -Developed—
1•38
RV Post -Developed-
1.83 In.
Q Developed <
1.19 cfs
Section B 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.
The limits of analysis ends at subareas A & B since "...subdivision 3 of this subsection is utilized
to show compliance with the channel protection criteria..."
9 VAC 25-870-66 Subareas A & B
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 "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."
Section C.3 Limits of Analysis
The analysis terminates at subareas A & B since subsection C.2.b is met.
Virginia Runoff Reduction Method Water Quality
Calculations
(COMPLIANCE IS MET THROUGH THE BEST MANAGEMENT PRACTICE OF PURCHASING NUTRIENT CREDITS.)
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