2-Combined Addendum and ditch calcs

Addendum to
Erosion Control Calculations
To include all diversion ditches
For
Wake Stone Corporation
Knightdale Quarry
Mining Permit No. 92-06
Wake County, North Carolina
2021 Mining Permit Modification
Dated: January 19, 2021
Prepared by:
L. Cole Atkins
Geologist/ Environmental Specialist
Wake Stone Corporation
PO Box 190
Knightdale, NC 27545

Diversion Ditch Sizing/Liner Calculations
Diversion
Drainage
Area (ac.)
Q2 (Pre-
Construction)
Q25 (during
and post-
construction)
Bottom
Width
(ft)
Side
Slope
(H:V)
Length
(ft)
Slope
(ft/ft)
Q25 Flow
Depth
(ft)
Design
Depth
(ft)
Pre-
Construction
Velocity (ft/s)
Post-
Construction
Velocity (ft/s)
Shear
Stress
(PSF)
Allowable
Shear Stress
(PSF)
Allowable
Velocity
NO
Temp Liner
Permanent Liner
1A
3.45
5.5 cfs
22.2 cfs
8
3:1
710
0.005
0.7
1.5
1.87
3.14
0.22
N/A
4.5
N/A
Vegetated (Grass)
1B
3.9
6.2 cfs
25.1 cfs
8
3:1
734
0.026
0.47
1
4.6
5.69
0.76
2
N/A
Straw with Net
Rip Rap 6" D50
2
2.1
3.1 cfs
13.5 cfs
12
6:1
990
0.027
0.6
1.5
0.89
1.45
1.01
2
N/A
Vegetated (Grass)
Rip Rap 6" D50
3
0.73
0.8 cfs
2.9 cfs
4
2:1
492
0.02
0.21
1
1.9
3.05
0.27
N/A
4.5
N/A
Vegetated (Grass)
4
0.75
0.9 cfs
3.0 cfs
4
2:1
679
0.009
0.28
1
1.55
2.38
0.16
N/A
4.5
N/A
Vegetated (Grass)
5A
0.43
0.6 cfs
2.8 cfs
6
2:1
244
0.041
0.13
1
1.84
3.32
0.34
N/A
4.5
N/A
Vegetated (Grass)
5B
0.8
1.1 cfs
5.2 cfs
12
6:1
126
0.016
0.34
1.5
0.52
1.1
0.63
2
N/A
Straw with Net
Rip Rap 6" D50
6
3.24
4.2 cfs
20.9 cfs
6
2:1
262
0.004
0.86
2
1.85
3.15
0.21
N/A
4.5
N/A
Vegetated (Grass)

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By: LCA 41111011 Date: 1/19/2022
Checked By: Date:
Company: WSC
Project Name: _ KDALE
Project No.: 1A-Pre
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is:
0 = CIA
where:
0 = peak rate of runoff in cubic feet per second (cfs)
C = runoff coefficient, an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensity of rainfall in uiches;hour, for a storm duration equal
to the time of concentration, Tc
A = drainage area in acres
The general procedure for determiitung peak discharge using the rational
formula is presented below and illustrated in Sample Problem 8.03a_
Step I Determine the drainage area in acres.
Total Drainage Area
3.45
Step 2. Determine the runoff coefficient. C. for the type of soil, cover in the
drainage area (Table 8.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
cover conditions. a weighted average must be calculated, or the area may be
subdivided,
Subarea A (acres)
Subarea A Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient
Step 3.
(Step 4.
2-year Rainfall Intensity, i (in/hr)
10-year Rainfall Intensity, i (in/hr)
25-year Rainfall Intensity, i (in/hr)
0.64
0.25 Runoff Coefficient
0.99
0.25
0.37
0.75
1.45
0.2
0.2826087
5.68
7.26
8.05
Step 5. Determine peak discharge. Q (cubic feet per second), by multiplying
the previously determined factors using the rational formula (Sample Problem
8.03a);
Q =CIA
Q2 Flow (cfs) 5.5
Quo Flow (cfs) 7.1
Q25 Flow (cfs) 7.8

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By:
Checked By: _
Company:
Project Name:
Proiect No.:
LCA Date:
Date:
WSC
KDALE
1 A -Post
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is
Q = CIA
1 /19/2022
where:
Q = peak rate of runoff in cubic feet per second (cfs)
C = runoff coefficient, an empirical coefficient representing the
relationship benveen rainfall rate and runoff rate
I = average intensity of rainfall in mchesRnour, for a storm duration equal
to the time of concentration, Tc
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented beloxv and illustrated in Sample Problem 8.03a.
Step 1. Determine the drainage area in acres.
Total Drainage Area
3.45
Step 2. Determine the runoff coefficient. C. for the type of soil,cover in the
drainage area (Table 8.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
cover conditions, a weighted average must be calculated. or the area may be
subdivided.
Subarea A (acres) 3.45
Subarea A Runoff Coefficient 0.8 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.8
Step 3.
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step 5. Determine peak- discharge. Q (cubic feet per second). by multiplying
the previously determined factors usuig the rational formula (Sample Problem
8.03a);
Q =CIA
Q2 Flow (cfs) 15.7
Q10 Flow (cfs) 20.0
Q25 Flow (cfs) 22.2

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User Input Data
Calculated Value
Reference Data
Designed By:
CA Date:
&
Checked By:
Date:
Company:
WSC
Project Name:
KDALE
Proiect No.:
1 B-Pre
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is
Q = CIA
where:
Q = peal: rate of runoff m cubic feet per second (cfs.)
C = nunoff coefficient, an empirical coefficient representing the
relation slup between rainfall rate and nutoff rate
I = average intensity of rainfall in inches hour. for a stone duration equal
to the time of concentration. Tc
A = drainage area in acres
The general procedure for determining peak discharge using the rational
fornnula is presented below and illustrated in Sample Problem 8.03a.
Step 1 Determine the drainage area in acres.
Total Drainage Area
3.9
Step 2. Determine the nunof} coefficient. C. for the npe of soil cover in the
drainage area (Table 8.03b)_

value can be determined directly from Table 8.03b. If there are multiple soil
comer conditions; a weighted average must be calculate& or the area may be
subdivided.
Subarea A (acres)
Subarea A Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient
Step 3.
Go to Intensity Worksheet
Step 4.
2-year Rainfall Intensity, i (in/hr)
10-year Rainfall Intensity, i (in/hr)
25-year Rainfall Intensity, i (in/hr)
0.45
0.25 Runoff Coefficient
1.63
0.25
0.37
0.75
1.45
0.2
0.2788462
5.68
7.26
8.05
Step S. Determine peak discharge. Q (cubic feet per second), by multiplying
the previously determined factors using the rational fornulla (Sample Problem
S.03a).
Q =CIA
Q2 Flow (cfs)
6.2
Quo Flow (cfs)
7.9
Q25 Flow (cfs)
8.8

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By: LCA Date: 1/19/2022
Checked By: Date: ft
Company: WSC
Project Name: KDALE
Proiect No.: 1 B-Post
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is:
Q=CIA
where:
Q = peak rate of runoff in cubic feet per second (cfs)
C = runoff coefficient. an empirical coefficient representing the
relationship between rainfall rate and rtmoff rate
I = average intensity of rainfall in inches1otu. for a storm duration equal
to the time of concentration, TC
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented below and illustrated in Sample Problem 8.03a.
Step 1. Determine the drainage area in acres.
Total Drainage Area
3.9
Step 2. Determine the runoff' coefficient. C. for the type of soil: cover in the
drainage area (Table 8.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
cover conditions. a weighted average must be calculated, or the area may be
subdivided.
Subarea A (acres) 3.9
Subarea A Runoff Coefficient 0.8 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.8
Step 3.
Go to Intensity Worksheet
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step -5. Determine peal discharge. Q (cubic feet per second), by multiplying
the previously determined factors cuing the rational formula (Sande Problem
8.03a);
Q =CIA
Q2 Flow (cfs) 17.7
Qio Flow (cfs) 22.7
Q25 Flow (cfs) 25.1

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By:
Checked By:
Company:
Project Name:
Project No.:
Site Location (City/Town)
Watershed Basin Id.
The rational formula is:
LCA
WSC
KDALE
2-Pre
Knightdale
201
0 = CIA
Date: 1 /19/2022
uate:
where:
0 = peak rate of runoff in cubic feet per second (cfs)
C = runoff coefficient, an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensity of rainfall in inches1our. for a storms duration equal
to the time of concentration, TC
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented beloxv and illustrated in Sample Problem 8.03a.
Step 1. Determine the drainage area in acres.
Total Drainage Area
2.1
Step 2. Determine the runoff coefficient. C. for the type of solUcover in the
drainage area (Table 8.03b).

value can be detemuned directly from Table 8.03b. If there are multiple soil
corer conditions. a weig..)lted average must be calculated, or the area may be
subdivided_
Subarea A (acres)
Subarea A Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient
Step 3.
Go to Intensity Worksheet
Step 4.
2-year Rainfall Intensity, i (in/hr)
10-year Rainfall Intensity, i (in/hr)
25-year Rainfall Intensity, i (in/hr)
1.36
0.25 Runoff Coefficient
0.7
0.25
0.04
0.75
0.2595238
5.68
7.26
8.05
Step 5. Deternune peak discharge. Q (cubic feet per second). by multiplying
the previously deternuned factors using the rational formula (Sample Problem
8.03a);
Q =CIA
Q2 Flow (cfs) 3.1
Q10 Flow (cfs) 4.0
Q25 Flow (cfs) 4.4

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By: LCA 'Date: 1/19/2022
Checked By: _Date:
Company: WSC
Project Name: KDALE
Project No.: 2-Post
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula i
Q=CIA
where:
Q = peak rate of runoff ui cubic feet per second (cfs)
C = runoff coefficient, an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensity of rainfall in inches hour, for a storm duration equal
to the time of concentration, TC
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented below and illustrated in Sample Problem 8.03a.
Step 1. Deternne the drainage area ui acres.
Total Drainage Area
2.1
Step 2. Determine the runoff coefficient. C. for the type of soiPcover in the
drainage area (Table 8.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
cover conditions, a weighted average must be calculated, or the area may be
Subdivided.
Subarea A (acres) 2.1
Subarea A Runoff Coefficient 0.8 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.8
(Step 3.
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step 5. Determine peak discharge, Q (cubic feet per second), by multiplying
the previously determined factors using the rational formula (Sample Problem
8.03a):
Q =CIA
Q2 Flow (cfs) 9.5
Q10 Flow (cfs) 12.2
Q25 Flow (cfs) 13.5

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By: LCA 'Date: 1/19/2022
Checked By: Date:
Company: WSC
Project Name: KDALE
Proiect No.: 3-Pre
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is:
Q=CIA
where:
Q = peak rate of runoff in cubic feet per second (cfs)
C = runoff coefficient. an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensity of rainfall in inches -hour. for a storm duration equal
to the time of concentration, Tc
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented below and illustrated in Sample Problem 8.03a.
Step 1. Determine the drainage area in acres.
Total Drainage Area
0.73
Step 2. Determine the runoff coefficient. C. for the type of soil/cover in the
drainage area (Table 8.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
cover conditions, a weighted average must be calculated or the area may be
subdivided.
Subarea A (acres) 0.73
Subarea A Runoff Coefficient 0.2 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.2
Step 3.
Go to Intensity Worksheet
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step 5. Determine peal discharge. Q (cubic feet per second), by multiplying
the previously determined factors using the rational formula (Sample Problem
8.03a).
Q =CIA
Q2 Flow (cfs) 0.8
Q10 Flow (cfs) 1.1
Q25 Flow (cfs) 1.2

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By: LCA A Date: 1/19/2022
Checked By: 40m Date:
Company: WS
p Y�
Project Name: KDAL"--
Project No.: 3-Post
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is:
0 = CIA
where:.
0 = peak rate of nuioff in cubic feet per second (cfs)
C = runoff coefficient. an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensity of rainfall m inches1oiu_ for a storm duration equal
to the time of concentration, TC
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented below and illustrated in Sample Problem 8.03a.
Step 1 _ Determine the drainage area in acres.
Total Drainage Area
0.73
Step 2. Determine the runoff coefficient. C. for the type of soiUcover in the
drainage area (Table 8.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
cover conditions, a weighted average must be calculated. or the area may be
subdivided.
Subarea A (acres) 0.73
Subarea A Runoff Coefficient 0.5 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.5
Step 3.
M
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step S. Determine peak discharge. Q (cubic feet per second, by multiplying
the previously determined factors using the rational fornu►la (Sample Problem
8.03a)_
Q =CIA
Q2 Flow (cfs) 2.1
Q10 Flow (cfs) 2.6
Q2s Flow (cfs) 2.9

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By:
Checked By:
Company:
Project Name:
Proiect No.:
LCA Date: 1 /19/2022
Date:
WSC
KDALE
4-Pre
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is:
Q=CIA
where:
Q = peak rate of runoff in cubic feet per second (cfs)
C = runoff coefficient. an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensinf of rainfall in inche0iour, for a storm duration equal
to the time of concentration, Tc
A = drainage area in acres
The general procedure for determining peak discharge using the rational
fornnula is presented below and illustrated in Sample Problem 8.03a.
Step 1 Determine the drainage area in acres.
Total Drainage Area
0.75
Step 2. Determine the runoff coefficient, C. for the type of soil/cover in the
drainage area (Table 8.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
corer conditions; a weighted average must be calculated, or the area may be
subdivided.
Subarea A (acres) 0.75
Subarea A Runoff Coefficient 0.2 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.2
Step 3.
M
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step 5. Determine peak disdiarge_ Q (cubic feet per second), by multiplying
the previously determined factors using the rational formula (Sample Problem
8.03a):
Q =CIA
Q2 Flow (cfs) 0.9
Quo Flow (cfs) 1.1
Q25 Flow (cfs) 1.2

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By: LCA `Date: 1/19/2022
Checked By: Date:
Company: WSC
Project Name: KDALE
Proiect No.: 4-Post
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is:
Q=CIA
where:
Q = peak rate of runoff ui cubic feet per second (cfs)
C = runoff coefficient, an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensity of rainfall in inches1otu, for a storm duration equal
to the time of concentration, TC
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented below and illustrated in Sample Problem 8.03a.
titer I Determne the drainage area in acres.
Total Drainage Area
0.75
Step 2. Determine the runoff coefficient, C, for the type of soil: cover in the
drainage area (Table 8.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
cover conditions, a weighted average must be calculated or the area may be.
subdivided.
Subarea A (acres) 0.75
Subarea A Runoff Coefficient 0.5 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.5
Step 3.
Go to Intensity Worksheet
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step 5. Determine peak discharge. Q (cubic feet per second), by multiplying
the previously determined factors using the rational formula (Sample Problem
8.03a).
Q =CIA
Q2 Flow (cfs) 2.1
Q10 Flow (cfs) 2.7
Q25 Flow (cfs) 3.0

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By: LCA Date: 1/19/2022
Checked By: Date:
Company: WSC
Project Name: KDALE
Proiect No.: 5A-Pre
Site Location (City/Town) Knightdalel
Watershed Basin Id. 201
The rational formula is:
C.1=CIA
where:
a = peak rate of runoff in cubic feet per second (cfs)
C = runoff coefficient, an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensity of rainfall in inches. -hour, for a storm duration equal
to the time of concentration, Tc
A = drainage area in acres
The general procedure for determuiung peak discharge using the rational
fonnula is presented below and illustrated in Sample Problem 8.03a_
Step 1. Determine the drainage area ui acres.
Total Drainage Area
MI
Step 2. Determine the runoff coefficient, C. for the type of soil'cocer in the
drainage area (Table 8.03b).

value can be determined directly from Table &03b. If there are multiple soil
corer conditions, a weighted average must be calculated, or the area may be
subdivided.
Subarea A (acres) 0.43
Subarea A Runoff Coefficient 0.25 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.25
Step 3.
M
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step 5. Determine peak- discharge. Q (cubic feet per second)_ by multiplying
the previously determined factors using the rational formula (Sample Problem
&03a).
Q =CIA
Q2 Flow (cfs)
0.6
Quo Flow (cfs)
0.8
Q25 Flow (cfs)
0.9

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By: LCA Date: 1/19/2022
Checked By: Date:
Company: WSC
Project Name: KDALE
Proiect No.: 5A-Post
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is:
Q=CIA
where:
Q = peak rate of runoff in cubic feet per second (cfs)
C = runoff coefficient, an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensity of rainfall in inches1otu. for a storm duration equal
to the time of concentration, Tc
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented beloxv and illustrated in Sample Problem 8.03a.
Step 1 Determne the drainage area ni acres.
Total Drainage Area
0.43
Step 2. Determine the runoff coefficient. C. for the type of soil%cover in the
drainage area (Table 8.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
cover conditions, a weighted average must be calculated. or the area may be
subdivided.
Subarea A (acres) 0.43
Subarea A Runoff Coefficient 0.8 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.8
Step 3.
Go to Intensity Worksheet
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step 5. Determine peak discharge. Q (cubic feet pet second), by multiplying
the previously determined factors using the rational formula (Sample Problem
8.03a):
Q =CIA
Q2 Flow (cfs)
2.0
Q10 Flow (cfs)
2.5
Q2s Flow (cfs)
2.8

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User Input Data
Calculated Value
Reference Data
Designed By: LCA Date: W1/194
0
Checked By: Date:
Company: WSC
Project Name: KDALE ;
Proiect No.: 5B-Pre
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational fonuWa is:
Q=CIA
where:
Q = peak rate of runoff ui cubic feet per second (cfs)
C = nmoff coefficient, an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensity of rainfall in inches.1our, for a storm duration equal
to the time of concentration, Tc
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented below and illustrated in Sample Problem 8.03a.
Step 1 Determine the drainage area in acres.
Total Drainage Area
Me
Step 2. Determine the runoff coefficient, C, for the type of soil.'cover in the
drainage area (Table 8.03b).

value can be deternwied directIv from Table 8.03b. If there are multiple soil
cover conditions. a weighted average must be calcidated. or the area may be
subdivided.
Subarea A (acres) 0.8
Subarea A Runoff Coefficient 0.25 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.25
Step 3.
Go to Intensity Worksheet
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step Derernutie peak discharge. Q (cubic feet per second). by multiplying
the previously detemwied factors usaia the rational formula (Sample Problem
S.03a).
Q --CIA
Q2 Flow (cfs) 1.1
Q10 Flow (cfs) 1.5
Q25 Flow (cfs) 1.6

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By: LCA "Date: 1/19/2022
Checked By: Date:
Company: WSC
Project Name: KDALE
Project No.: 56-Post
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is:
Q=CIA
where:
Q = peak rate of runoff in cubic feet per second (cfs)
C = runoff coefficient, an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensity of rainfall in inches1our, for a storm duration equal
to the time of concentration, TC
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented below and illustrated in Sample Problem 8.03a.
Step I. Determine the drainage area in acres.
Total Drainage Area
Step 2. Determine the runoff coefficient, C. for the type of soil.'cover ui the
drainage area (Table 8.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
cover conditions, a weighted average must be calculated, or the area may be
subdivided.
Subarea A (acres) 0.8
Subarea A Runoff Coefficient 0.8 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.8
Step 3.
Go to Inte
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step 5. Determine peak discharge. Q (cubic feet per second), by multiplying
the previously determined factors using the rational formula (Sample Problem
8.03a).
Q =CIA
Q2 Flow (cfs) 3.6
Quo Flow (cfs) 4.6
Q25 Flow (cfs) 5.2

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By: LCA Date: 1/19/2022
Checked By: Date:
Company: WSC
Project Name: KDALE
Proiect No.: 6-Pre
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is:
Q = CIA
where:
Q = peak rate of runoff in cubic feet per second (cfs)
C = runoff coefficient, an empirical coefficient representing the
relationship between rainfall rate and runoff rate
1 = average intensity of rainfall in inches,'hour. for a storm duration equal
to the time of concentration, Tc
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented below and illustrated in Sample Problem 8.03a.
Step 1. Determine the drainage area in aces.
Total Drainage Area
3.24
Step ?. Determine the runoff coefficient, C. for the type of soil,'cover in the
drainage area (Table 8.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
cover conditions, a weighted average mist be calculated, or the area may be
subdivided.
Subarea A (acres)
Subarea A Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient
Step 3.
Step 4.
2-year Rainfall Intensity, i (in/hr)
10-year Rainfall Intensity, i (in/hr)
25-year Rainfall Intensity, i (in/hr)
2.38
0.2 Runoff Coefficient
0.6
0.1
0.26
0.8
0.2296296
5.68
7.26
8.05
Step 5. Determine peak discharge. Q (cubic feet per second), by multiplying
the previously determined factors using the rational formula (Sample Problem
8.03a).
Q =CIA
Q2 Flow (cfs)
4.2
Quo Flow (cfs)
5.4
Q25 Flow (cfs)
6.0

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Rational Method
User Input Data
Calculated Value
Reference Data
Designed By: LCA Date: 1/19/2022
Checked By: Date:
Company: WSC
Project Name: KDALE
Proiect No.: 6-Post
Site Location (City/Town) Knightdale
Watershed Basin Id. 201
The rational formula is:
Q=CIA
where:
Q = peak rate of runoff in cubic feet per second (cfs)
C = runoff coefficient. an empirical coefficient representing the
relationship between rainfall rate and runoff rate
I = average intensity of rainfall in inches1our_ for a storm duration equal
to the time of concentration, Tc
A = drainage area in acres
The general procedure for determining peak discharge using the rational
formula is presented below and illustrated in Sample Problem 8.03a.
Step 1. Deterinme the drainage area in acres.
Total Drainage Area
3.24
',+tep _ Dett uinmie the nunoffcoefficient. C. for the type of soiPcover in the
, name area ( Table €.03b).

value can be determined directly from Table 8.03b. If there are multiple soil
cover conditions, a weighted average must be calculated or the area may be
subdivided.
Subarea A (acres) 3.24
Subarea A Runoff Coefficient 0.8 Runoff Coefficient
Subarea B (acres)
Subarea B Runoff Coefficient
Subarea C (acres)
Subarea C Runoff Coefficient
Subarea D (acres)
Subarea D Runoff Coefficient
Weighted Runoff Coefficient 0.8
Step 3.
Go to Intensity Worksheet
Step 4.
2-year Rainfall Intensity, i (in/hr) 5.68
10-year Rainfall Intensity, i (in/hr) 7.26
25-year Rainfall Intensity, i (in/hr) 8.05
Step 5. Detenme peak discharge. Q (cubic feet per second), by multiplying
the previously determined factors using the rational formula (Sample Problem
8.03a);
Q =CIA
Q2 Flow (cfs) 14.7
Q10 Flow (cfs) 18.8
Q25 Flow (cfs) 20.9

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