Instruction Flow Chart
Fill in site's Pre‐Development parameters on 'Pre' tab (Site Area, Drainage Area, Impervious Area, CNpre, tc)
Prior to using BSD or BMP practices, fill in site's Post‐Development parameters on 'Post' tab (Impervious Area, CNpre, tc)
Will the site incorporate BSD or BMP Pre-Devel. Peak flows
Results shown on 'Detailed Summary' tab
Post-Devel. Peak flows,
Post Storage Volumes
NO
Use storage volumes and peak flows from the 'Post' tab for final pond design. YES
Using BSD Practices Only
Use 'BSD_Credits' tab if site preserves 1) Natural Conservation Areas, 2) Stream Buffers, 3) Vegetated Channels 4) Infiltration Zones and/or 5) Env. sensitive large lot subdivisions
New WQv'
Using BMP Practices Did the Site use practices 1), 2) NO
Use the same CNpost from
the 'Post' tab and input this value in the 'Post_BSD' tab. New
WQv'
Use storage volumes and peak flows from the 'Post_BSD' tab for final pond design. YES
Use 'CN_BSD' tab to calculate site's new CN'post to be used for site runoff reduction calculations
New
CN'post
Use CN'post from the 'CN_BSD' tab and input this value in the 'Post_BSD' tab. Site to also include upland BMPs?
New
WQv'
New
Storage
Vs
Use storage volumes and peak flows from the 'Post_BSD' tab for final pond NO
YES
Size BMPs using either the City's 6 separate Design Aid sheets or other calculation method to determine BMP's storage volume (Vs)
Use 'BMP_Credits' tab to input storage volumes BMP practice detains
New WQv"
Did the Site use BSD practices,
Bioretention, Infiltration Trench, Porous Surfaces, Dry Swale, and/or Rain Garden/Cistern?
YES
NO
YES
Use 'CN_BMP' tab to calculate site's new CN"post for site runoff reduction calculations
Did the site use BSD practices AND adjust the CN (CN'post)?
NO
New
CN"post
Use CN"post from 'CN_BMP' tab ; input value in 'Post_BSD+BMP' tab. Use same CN'post from 'Post_BSD' tab; input value in 'Post_BSD+BMP' tab. Use same CNpost from 'Post' tab;
input value in 'Post_BSD+BMP' tab. New WQv"
New Storage Vs
Use storage volumes and peak flows from New
WQv" 'Post_BSD+BMP' tab for final pond design. Use storage volumes and peak flows from 'Post_BSD+BMP' tab for final pond design. Detailed Summary
Site Hydrology
Drainage
Area [ac]
Pre-Development
Post-Development
Pre-Development
Post-Development
Imperv.
Area [ac]
38
0
38
13.8
1yr [cfs]
Qpw [cfs]
N/A
4
WQv [cf]
tc
65
78
0.32
0.17
2yr [cfs] 10yr [cfs] 25yr [cfs]
22.4
68.1
CPv [cf]
62,378
Pre-Development
Post-Development
CN
125,308
29.6
80.8
79.9
167.3
2yr [cf]
10yr [cf]
77,176
130,608
99.0
198.6
100yr
[cfs]
148.7
267.4
25yr [cf] 100yr [cf]
150,386
186,860
Better Site Design
Credited Practice
Applicable BSD Credits to Adjust Site's
CN:
WQv Credit [cf]
Natural Area Conservation
Stream Buffer
Vegetated Channel
Overland Flow Filtration/Infiltration Zones
Environmentally Sensitive Large Lot
11,491
8,208
20,519
821
Conservation Areas
Stream Buffers
Infiltration Zones
11,491 cf
8,208 cf
821 cf
20,519 cf
Total V stored with BSD practices
41,038
Adjustment to
Runoff Reduction
Volume (BSD)
New Water WQv'
21,340
Adjusted CNpost'
Drainage
Area [ac]
Post-Development
Post-Dev. with BSD
Post-Development
Post-Dev. with BSD
-
Imperv.
Area [ac]
38
13.8
38
13.8
Qpw [cfs]
N/A
WQv [cf]
Post-Development
Post-Dev. with BSD
62,378
21,339
1yr [cfs]
68.1
64.9
CPv [cf]
125,308
119,506
CN
tc [hrs]
78
77
0.17
0.17
2yr [cfs] 10yr [cfs] 25yr [cfs]
80.8
77.3
167.3
162.4
2yr [cf]
10yr [cf]
77,176
71,977
130,608
124,205
Page 1
198.6
193.3
100yr
[cfs]
267.4
261.6
25yr [cf] 100yr [cf]
150,386
143,651
186,860
179,672
77
Detailed Summary
Better Site Design & Structural BMPs
Credited Practices in CoC BMP Manual
6,186
8,102
1,000
-
Bioretention Area
Infiltration Trench
Grass Filter Strip
Dry Swale
Pervious Surfaces
Credited Practices for Other Accepted
Structural BMPs
Wetlands
Wet Swale
Gravity Separator
Commercial SW Controls
Multi-Purpose Dention Area
Underground Detention
Rain Garden/Cistern
Total V stored with BSD practices
New Water WQv"
Post-Development
Post-Dev. with BSD
Post-Dev. with BSD & BMPs
Post-Development
Post-Dev. with BSD
Post-Dev. with BSD & BMPs
Qpw [cfs]
N/A
62,378
21,339
6,051
Applicable BMP Credits to Adjust Site's
CN:
Bioretention
6,186 cf
Infiltration Trench
8,102 cf
Porous Surfaces
cf
Dry Swale
cf
Rain Garden/Cistern
cf
Runoff Reduction
34,807 cf
Vol. Adjustment
(BSD + BMP)
Adjusted CN"post
76
WQv Credit [cf]
15,288
6,051
Imperviou
Total
s Area
Drainage
Area [acres]
[acres]
38
13.8
38
13.8
38
13.8
WQv [cf]
Post-Development
Post-Dev. with BSD
Post-Dev. with BSD & BMPs
Applicable BSD Credits to Adjust Site's
CN:
Conservation Areas
11,491 cf
Stream Buffers
8,208 cf
Infiltration Zones
821 cf
WQv Credit [cf]
1yr [cfs]
68.1
64.9
61.9
CPv [cf]
125,308
119,506
113,861
CN
tc
78
77
76
0.17
0.17
0.17
2yr [cfs] 10yr [cfs] 25yr [cfs]
80.8
77.3
74.0
167.3
162.4
157.6
2yr [cf]
10yr [cf]
77,176
71,977
66,987
130,608
124,205
117,954
Page 2
198.6
193.3
188.1
100yr
[cfs]
267.4
261.6
255.7
25yr [cf] 100yr [cf]
150,386
143,651
137,045
186,860
179,672
172,561
Pre-Development
Site Information
Site Area
Total Drainage Area
Impervious Area
CNpre
tc
S
Ia
38
38
0
65
0.32
5.385
1.077
acres
acres
acres
data input cells
calculation cells
constant values
hours
Peak Flow
Storm
Precipitation
(P), [inches]
(Richland Co.,
Type II)
1-year storm
2-year storm
10-year storm
25-year storm
100-year storm
3.36
3.7
5.7
6.4
7.9
Runoff
(Q),
[inches]
0.680
0.859
2.136
2.646
3.814
Ia/P
qu
[csm/in]
0.321
0.291
0.189
0.168
0.136
Equations
S = 1000/CN - 10
Ia = 0.2S
log (qu) = C0 + C1*log tc + C2(log tc)2
Q = (9-0.2*S)^2 / (P+0.8*S)
Qp= qu*A*Q
C0,C1,C2 coefficients depend on SCS type rainfall (Type II on sheet 'qu_Pre')
555.7
579.4
629.9
629.9
656.8
Peak
Discharge
(Qppre), [cfs]
22.4
29.6
79.9
99.0
148.7
Post-Development
Without Better Site Design and Without Upland BMPs
Site Information
Site Area
Total Drainage Area
Impervious Area
CNpost
tc
S
Ia
Water Quality Volume, WQv
38
38
13.8
78
0.17
2.821
0.564
ac
ac
ac
Impervious Area, I
R
WQv
WQv
hrs
R = 0.05 + 0.009*I
WQv = 1.2 * R * A / 12
Channel Protection Volume, CPv
1-year precip.
Runoff, Q
Ia/P
qu
Peak flow, Qppost
qu/qi
Vs/Vr
CPv
CPv
3.36
1.392
0.168
824.0
68.1
25-Year Storage Volume
inches
inches
25-yr precip.
Runoff, Q
Ia/P
qu
Qppost = qi
csm/in
cfs
Q = (P-0.2*S)^2 / (P+0.8*S)
2
log (qu) = C 0 + C 1 *log tc + C 2 (log tc)
Qp= qu*A*Q
qu/qi: Must detain for 24 hr, see 'qu_qi' tab
Vs/Vr = 0.682-1.43(qu/qi)+1.64(qu/qi)^2-0.804(qu/qi)^3
CPv = (Vs/Vr)*Q*A/12
2-year storm
10-year storm
100-year storm
Precip.
[inches]
Q [inches]
3.7
5.7
7.9
1.65
3.32
5.30
qo/qi
2-year storm
10-year storm
100-year storm
0.37
0.48
0.56
Q = (P-0.2*S)^2 / (P+0.8*S)
log (qu) = C 0 + C 1 *log tc + C 2 (log tc) 2
Qp= qu*A*Q
Vr = Q (A/640) 53.33, where A = Sq. miles
qo= predevelopment peak flow for 2-yr, 10-yr and 100-yr
Vs/Vr = 0.682-1.43(Qo/Qi)+1.64(Qo/Qi)^2-0.804(Qo/Qi)^3
Vs = Vr (Vs/Vr)
6.40
3.934
0.088
850.1
198.6
Qppre = qo
qo/qi
Vs/Vr
Vr
Vs, 25-yr
Vs, 25-yr
0.021
0.653
2.88 ac-ft
125,308 cf
Storm
36.3 %
0.377
1.432 ac-ft
62,378 cf
99.0
0.50
0.277
12.46
3.45
150,386
inches
inches
csm/in
cfs
cfs
ac-ft
ac-ft
cf
Q = (P-0.2*S)^2 / (P+0.8*S)
2
log (qu) = C 0 + C 1 *log tc + C 2 (log tc)
Qp= qu*A*Q
Vr = Q (A/640) 53.33, where A = Sq. miles
qo= predevelopment peak flow for 25-yr
Vs/Vr = 0.682-1.43(Qo/Qi)+1.64(Qo/Qi)^2-0.804(Qo/Qi)^3
Vs = Vr (Vs/Vr)
Ia/P
0.15
0.10
0.07
Vs/Vr
0.339
0.286
0.256
qu [csm/in]
824.0
850.1
850.1
Vr [ac.ft]
Qppre (qo), Qppost (qi),
[cfs]
[cfs]
29.6
80.8
79.9
167.3
148.7
267.4
Vs [ac.ft]
5.23
10.50
16.78
1.77
3.00
4.29
Vs [cf]
77,176
130,608
186,860
Better Site Design (BSD) Credits - <FORMAT 1>
Better Site Design Practice Stormwater Credits Summary
Practice
Description
Natural area conservation
Undisturbed natural areas are conserved on a site,
thereby retaining their pre-development hydrologic
and water quality characteristics.
Stream buffers
Stormwater runoff is treated by directing sheet flow
runoff through a naturally vegetated or forested buffer
as overland flow.
Use of vegetated channels
Vegetated channels are used to provide stormwater
treatment.
Overland flow
filtration/infiltration zones
Overland flow filtration/infiltration zones are
incorporated into the site design to receive runoff from
rooftops and other small impervious areas.
Environmentally sensitive
large lot subdivisions
A group of site design techniques are applied to low
and very low density residential development.
Site's New Water Quality
WQv'
21,339
cu.ft
Natural Area Conservation Credits
Criteria:
Site Drainage Area, A
Impervious Area, I
Natural Conservation Area
New Drainage Area, A'
R
WQv, before credit
WQv, before credit
WQv', with credit
WQv', with credit
potential list of design criteria listed in the
Design Manual (or GSMM)
38 ac
13.8 ac
7 ac
31 ac
0.377
1.432 ac-ft
62,378 ac-ft
1.17 ac-ft
50,887 cf
18.4 % reduction in water quality volume
Stream Buffer Credits
Site Drainage Area, A
Impervious Area, I
Area Draining to Buffer
New Drainage Area, A'
R
WQv, before credit
WQv, before credit
WQv', with credit
WQv', with credit
Criteria:
38 ac
13.8 ac
5 ac
33 ac
0.377
1.432 ac-ft
62,378 cf
1.24 ac-ft
54,170 cf
13.2 % reduction in water quality volume
potential list of design criteria listed in the
Design Manual (or GSMM)
Vegetated Channel Credits
Criteria:
Site Drainage Area, A
Impervious Area, I
Area Draining to Buffer
New Drainage Area, A'
R
WQv, before credit
WQv, before credit
WQv', with credit
WQv', with credit
potential list of design criteria listed in the
Design Manual (or GSMM)
38 ac
13.8 ac
12.5 ac
25.5 ac
0.377
1.432 ac-ft
62,378 ac-ft
0.96 ac-ft
41,859 cf
32.9 % reduction in water quality volume
Overland Flow Filtration/Groundwater Recharge Zone Credits
Site Drainage Area, A
38 ac
Impervious Area, I
13.8 ac
Disconnected Impervious Area
0.5 ac
New Drainage Area, A'
37.5 ac
R
0.377
WQv, before credit
1.432 ac-ft
WQv, before credit
62,378 ac-ft
WQv', with credit
1.41 ac-ft
WQv', with credit
61,557 cf
1.3 % reduction in water quality volume
Environmentally Sensitive Large Lot Subdivision Credits
Criteria:
potential list of design criteria listed in the
Design Manual (or GSMM)
Criteria:
potential list of design criteria listed in the
Design Manual (or GSMM)
This crredit could be excluded
due to lack of potential use
62,378
62,378
0.0 % reduction in water quality volume
Better Site Design (BSD) Credits <FORMAT 2>
Better Site Design Practice Stormwater Credits Summary
Practice
Natural area conservation
Description
Undisturbed natural areas are conserved on a site, thereby retaining their predevelopment hydrologic and water quality characteristics.
Stream buffers
Stormwater runoff is treated by directing sheet flow runoff through a naturally vegetated
or forested buffer as overland flow.
Vegetated channels are used to provide stormwater treatment.
Use of vegetated channels
Overland flow
filtration/infiltration zones
Environmentally sensitive
large lot subdivisions
Overland flow filtration/infiltration zones are incorporated into the site design to receive
runoff from rooftops and other small impervious areas.
A group of site design techniques are applied to low and very low density residential
development.
Natural Area Conservation
Vegetated Channel
Site Drainage Area, A
Impervious Area, I
Natural Conservation Area
New Drainage Area, A'
R
WQv, before credit
WQv, before credit
WQv', with credit
WQv', with credit
38 ac
13.8 ac
7 ac
31 ac
0.377
1.432 ac.ft
62,378 cu.ft
1.17 ac.ft
50,887 cu.ft
18.4 % reduction in WQv
Site Drainage Area, A
Impervious Area, I
Area Draining to Buffer
New Drainage Area, A'
R
WQv, before credit
WQv, before credit
WQv', with credit
WQv', with credit
38 ac
13.8 ac
5 ac
33 ac
0.377
1.432 ac.ft
62,378 cu.ft
1.24 ac.ft
54,170 cu.ft
13.2 % reduction in WQv
Site Drainage Area, A
Impervious Area, I
Disconnected Impervious Area
New Drainage Area, A'
R
WQv, before credit
WQv, before credit
WQv', with credit
WQv', with credit
Stream Buffer
Site Drainage Area, A
Impervious Area, I
Area Draining to Buffer
New Drainage Area, A'
R
WQv, before credit
WQv, before credit
WQv', with credit
WQv', with credit
38 ac
13.8 ac
12.5 ac
25.5 ac
0.377
1.432 ac.ft
62,378 cu.ft
0.96 ac.ft
41,859 cu.ft
32.9 % reduction in WQv
Overland Flow/Groundwater Recharge
38 ac
13.8 ac
0.5 ac
37.5 ac
0.377
1.432 ac.ft
62,378 cu.ft
1.41 ac.ft
61,557 cu.ft
1.3 % reduction in WQv
Environ. Sensitive Large Lot Subdivision
Revised Water Quality Volume
WQv'
21,339
cf
This crredit could be excluded due
to lack of potential use
62,378
62,378
Post-Development: Better Site Design Site
Utilizing Better Site Design Credits, but No Upland BMPs
Site Information
Drainage Area, A
Impervious Area
CN'post
tc
S
Ia
*Adjust CN via 'CN_BSD' tab
Water Quality Volume, WQv'
38 ac
13.8 ac
77
0.17 hrs
2.987
0.597
Credited Areas
New Drainage Area, A'
Impervious Area, I
R
WQv, before credits
WQv': BSD credits
WQv': BSD credits
Channel Protection Volume, CPv
P,1-year storm
Runoff, Q'
Ia'/P
qu'
Peak flow, Qp'post
qu/qi'
Vs'/Vr'
CPv'
CPv'
2-year storm
10-year storm
100-year storm
2-year storm
10-year storm
100-year storm
ac
ac
%
cf
ac-ft
cf
25 Year Storage Volume
3.36
1.327
0.178
824.0
64.9
inches
inches
P,25-year storm
Runoff, Q'
Ia'/P
qu'
Qp'post = qi'
csm/in
cfs
Precip.
[inches]
Q' [inches]
3.7
5.7
7.9
6.40
3.831
0.093
850.1
193.3
Qppre = qo
qo/qi'
Vs'/Vr'
Vr'
Vs', 25-yr
Vs', 25-yr
0.021
0.653
2.74 ac-ft
119,506 cf
Storm
25
13
36.3
0.377
62,378
0.490
21,339
Ia'/P
1.58
3.22
5.18
0.16
0.10
0.08
qo/qi'
0.38
0.49
0.57
Vs'/Vr'
0.330
0.280
0.251
99.0
0.51
0.272
12.13
3.30
143,651
Qppre (qo),
[cfs]
qu' [csm/in]
824.0
850.1
850.1
Vr' [ac.ft]
5.01
10.19
16.41
29.6
79.9
148.7
Vs' [ac.ft]
1.65
2.85
4.12
inches
inches
csm/in
cfs
cfs
ac-ft
ac-ft
cf
Qppost' (qi'),
[cfs]
77.3
162.4
261.6
Vs' [cf]
71,977
124,205
179,672
Adjusted Curve Number, CN'
Site Utilizing Better Site Design Credits, but No Upland BMPs
IF Site Soils are homogeneous, then determine the adjusted CN with procedure below:
Step
1:
S
1
Determine the CN
C multiplier based on the site's imperviousness
% Impervious
36.3
36 3
Hydrologic Soil Group
C
A B
A,
B, C
C, or D
Use Figure below to determine site's
site s CN multiplier:
CN Multiplier
Step 2:
0.958
Calculate adjusted CN
CNpost
Adjusted CNpost'
78
75
il are NOT h
t
i adjusted
dj t d CN with
ith procedure
d
b
l
IF Sit
Site S
Soils
homogeneous, d
determine
below:
Applicable BSD Credits to Adjust Site's
Site s CN:
C
ti A
Conservation
Areas
Stream Buffers
Infiltration Zones
Site Data:
Site Drainage Area
Adjustment
j
to Runoff Reduction Volume
(BSD)
CN
t
CNpost
S
11 491 cff
11,491
8,208 cf
821 cf
38 ac
20 519 cf
20,519
78
2.82
C l l t Site
Sit Runoff
R
ff with
ith and
d without
ith t BMP
d th
dj t d CN
Calculate
BMPs and
the adjusted
CN:
Storm Event
1-yr
2-yr
10-yr
1
yr
2
yr
10 yr
P [inches]
3.36
3.7
5.7
3 36
37
57
Qpost:
p
no runoff red. credits [[in]]
1.39
1.65
3.32
Qpost: runoff reduction credits [in]
1.24
1.50
3.17
1 24
1 50
3 17
Adj t d CNpost'
75 6
75 8
76
4
Adjusted
75.6
75.8
76.4
Adjusted
Adj t d CNppost'
77
*to
to be conservative
conservative, use 100-yr CN post ' for Post_BSD
Post BSD calculations
25-yr
25
yr
6.4
64
3.93
3.79
3 79
76 5
76.5
100-yr
100
yr
7.9
79
5.30
5.15
5 15
76 7
76.7
Best Management Practices (BMP) Credits
Structural BMPs Designed for Site
BMPs in City of Columbia's BMP Manual:
Water Quality Volume
Credited Practice
Stored, WQv [cf]
6,186
Bioretention Area
8,102
Infiltration Trench
1,000
Grass Filter Strip
Dry Swale
Pervious Surfaces
Retrieve WQ Volumes from BMP Design Aid Worksheet
Other Accepted Structural BMPs:
Water Quality Volume
Credited Practice
Stored, WQv [cf]
Wetlands
Wet Swale
Gravity Separator
Commercial SW Controls
Multi-Purpose Dention Area
Underground Detention
Rain Garden/Cistern
Provide Supporting Calcultions for WQ Volumes
Site's Remaining Water Quality Volume
(for a pond):
WQv"
6,051
cu.ft
Post-Development: Structural BMPs
Site Utilizing Better Site Design Credits and Upland BMPs
Site Information
Water Quality Volume, WQv"
Total Drainage Area, A
Impervious Area
CN'post
38 ac
13.8 ac
76
tc
S
Ia
*Adjust CN via 'CN_BMP' tab
0.17 hrs
3.158
0.632
WQv, before credits
WQv', with BSD credits
WQv stored with BMPs
WQv", with all credits
Channel Protection Volume, CPv
P,1-year storm
Runoff, Q'
Ia'/P
qu'
Peak flow, Qp'post
qu/qi'
Vs'/Vr'
CPv'
CPv'
2-year storm
10-year storm
100-year storm
2-year storm
10-year storm
100-year storm
6,051 cf
25 Year Storage Volume
3.36
1.265
0.188
824.0
61.9
inches
inches
P,25-year storm
Runoff, Q'
Ia'/P
qu'
Qp'post = qi'
csm/in
cfs
Qppre = qo
qo/qi'
Vs'/Vr'
Vr'
Vs', 25-yr
Vs', 25-yr
0.021
0.653
2.61 ac-ft
113,861 cf
Storm
62,378 cf
21,339 ac-ft
15,288 cf
Precip. [in]
3.7
5.7
7.9
Q' [in]
1.51
3.12
5.07
qo/qi'
0.40
0.51
0.58
Ia'/P
0.17
0.11
0.08
Vs'/Vr'
0.321
0.274
0.247
6.40
3.728
0.099
850.1
188.1
99.0
0.53
0.267
11.80
3.15
137,045
inches
inches
csm/in
cfs
cfs
ac-ft
ac-ft
cf
Qppre (qo)
Qp'post
[cfs]
(qi) [cfs]
824.0
29.6
74.0
850.1
79.9
157.6
850.1
148.7
255.7
Vr' [ac.ft]
Vs' [ac.ft]
Vs' [cu.ft]
4.79
1.54
66,987
9.89
2.71
117,954
16.04
3.96
172,561
qu' [csm/in]
Adjusted Curve Number, CN"
Site Utilizing Better Site Design Credits and Upland BMPs
IF Site Soils are homogeneous, then determine the adjusted CN with procedure below:
Step 1:
Determine the CN multiplier based on the site's imperviousness
% Impervious
36.3
Hydrologic Soil Group
C
A, B, C, or D
Use Figure below to determine site's CN multiplier:
CN Multiplier
Step 2:
0.958
Calculate adjusted CN
CNpost
Adjusted CN"post
78
75
IF Site Soils are NOT homogeneous, determine adjusted CN with procedure below:
Applicable BSD Credits to Adjust Site's CN:
Conservation Areas
Stream Buffers
Infiltration Zones
Applicable BMP Credits to Adjust Site's CN:
Bioretention
Infiltration Trench
Porous Surfaces
Dry Swale
Rain Garden/Cistern
Site Data:
Site Drainage Area
Adjustment to Runoff Reduction Volume
(BSD)
CNpost
S
11,491 cf
8,208 cf
821 cf
6,186
8,102
1,000
-
cf
cf
cf
cf
cf
38 ac
35,807 cf
78
2.82
Calculate Site Runoff with and without BMPs and the adjusted CN:
Storm Event
1-yr
2-yr
P [inches]
3.36
3.7
Qpost: no runoff red. credits [in]
1.39
1.65
Qpost: runoff reduction credits [in]
1.13
1.39
Adjusted CNpost''
73.7
74.1
Adjusted CN"post
76
*to be conservative, use 100-yr CN"post for Post_BSD calculations
10-yr
5.7
3.32
3.06
75.2
25-yr
6.4
3.93
3.67
75.4
100-yr
7.9
5.30
5.04
75.7