SW3240704_Stormwater Report_20240805

EROSION CONTROL AND STORMWATER
MANAGEMENT REPORT
FOR:
HIDDEN ESTATES
WEDDINGTON, NC
PREPARED FOR:
ENCOMPASS BUILDING GROUP, LLC
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Ld ` THOMAS
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SEAL _ _ & HUTTON
- 050698 = •= ENGINEERING
05 13-2024 F F•' No F-0871 •'o
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J -#29589.0000
FEBRUARY 16, 2024
Prepared by:
HT THOMAS & HUTTON

EROSION CONTROL AND STORMWATER MANAGEMENT REPORT
Project: Hidden Estates
T&H Job Number: J-29589.0000
Location: Beulah Church Road
Weddington, NC 28173
Date Prepared: February 16, 2024
Owner: Encompass Building Group, LLC
Owner Address: 1016 Waxhaw/Indian Trail Rd.
Indian Trail, NC 28104
Engineer: Thomas & Hutton
Engineer Address: 1020 Euclid Avenue
Charlotte, NC 28203
Phone: [phone]
THOMAS & HUTTON

TABLE OF CONTENTS
Section 1 Channel Analysis
Section 2 Rip Rap Outlet Protection
Section 3 HEC-22 Stormwater Analysis
H THOMAS & HUTTON
Page 2

EROSION CONTROL AND STORMWATER
CALCULATIONS
HIDDEN ESTATES
SECTION i
CHANNEL ANALYSIS
29589.0000
ITI THOMAS Sc HUTTON

Channel Report
Hydraflow Express Extension for Autodesk®Civil 3D®by Autodesk, Inc. Friday, Feb 16 2024
Swale 01
Triangular Highlighted
Side Slopes (z:1) = 3.00, 5.00 Depth (ft) = 0.53
Total Depth (ft) = 1.00 Q (cfs) = 4.560
Area (sqft) = 1.12
Invert Elev (ft) = 689.97 Velocity (ft/s) = 4.06
Slope (%) = 4.45 Wetted Perim (ft) = 4.38
N-Value = 0.030 Crit Depth, Yc (ft) = 0.61
Top Width (ft) = 4.24
Calculations EGL (ft) = 0.79
Compute by: Known Q
Known Q (cfs) = 4.56
Elev (ft) Section Depth (ft)
691.00 , 1.03
690.50 0.53
690.00 0.03
689.50 -0.47
689.00 -0.97
0 1 2 3 4 5 6 7 8 9 10
Reach (ft)

29589.0000- Hidden Estates
Temporary Diversion Swale Calculations
2/16/2024
TDS-01
C i A Q TOP 689.97
(in/hr) (ac) (cfs) BOT 665.5
0.60 8.35 0.91 4.56 LENGTH 550
SLOPE 4.45%

2/16/24,9:28 AM ECMDS 7.0
NORTH North American Green
AMERICAN 5401 St. Wendel-Cynthiana Rd.
Poseyville, Indiana 47633
GREEN Tel. [phone]
>Fax [phone]
www.nagreen.com
ECMDS v7.0
CHANNEL ANALYSIS
>>>Swale 01
Name Swale 01
Discharge 4.56
Channel Slope 0.0445
Channel Bottom Width 0
Left Side Slope 3
Right Side Slope 5
Low Flow Liner
Retardence Class C 6-12 in
Vegetation Type Mix(Sod and Bunch)
Vegetation Density Very Good 80-95%
Soil Type Clay Loam(CL)
S75
Normal Permissible Calculated Safety Staple
Phase Reach Discharge Velocity Mannings N Remarks
Depth Shear Stress Shear Stress Factor Pattern
S75 Unvegetated Straight 4.56 cfs 4.04 ft/s 0.53 ft 0.031 1.6 lbs/ft2 1.47 lbs/ft2 1.09 STABLE D
Underlying Straight 4.56 cfs 4.04 ft/s 0.53 ft 0.031 1.74 Ibs/ft2 0.71 Ibs/ft2 2.44 STABLE D
Substrate
Unreinforced Vegetation
Normal Permissible Calculated Safety Staple
Phase Reach Discharge Velocity Mannings N Remarks
Depth Shear Stress Shear Stress Factor Pattern
Unreinforced Straight 4.56 cfs 2.85 ft/s 0.63 ft 0.05 4 Ibs/ft2 1.76 lbs/ft2 2.28 STABLE --
Vegetation
Underlying Straight 4.56 cfs 2.85 ft/s 0.63 ft 0.05 4 Ibs/ft2 0.85 lbs/ft2 4.7 STABLE --
Substrate
S75BN
Normal Permissible Calculated Safety Staple
Phase Reach Discharge Velocity Mannings N Remarks
Depth Shear Stress Shear Stress Factor Pattern
S75BN Straight 4.56 cfs 4.04 ft/s 0.53 ft 0.031 1.6 lbs/ft2 1.47 lbs/ft2 1.09 STABLE D
Unvegetated
Underlying Straight 4.56 cfs 4.04 ft/s 0.53 ft 0.031 1.74 lbs/ft2 0.71 lbs/ft2 2.44 STABLE D
Substrate
DS75
Normal Permissible Calculated Safety Staple
Phase Reach Discharge Velocity Mannings N Remarks
Depth Shear Stress Shear Stress Factor Pattern
DS75 Straight 4.56 cfs 4.04 ft/s 0.53 ft 0.031 1.6 lbs/ft2 1.47 lbs/ft2 1.09 STABLE D
Unvegetated
Underlying Straight 4.56 cfs 4.04 ft/s 0.53 ft 0.031 1.74 lbs/ft2 0.71 lbs/ft2 2.44 STABLE D
Substrate
https://ecmds.com/project/158279/channel-analysis/253246/show 1/2

2/16/24,9:28 AM ECMDS 7.0
https://ecmds.com/project/158279/channel-analysis/253246/show 2/2

2/16/24,9:29 AM ECMDS 7.0
NORTH North American Green
AMERICAN 5401 St. Wendel-Cynthiana Rd.
Poseyville, Indiana 47633
GREEN Tel. [phone]
>Fax [phone]
www.nagreen.com
ECMDS v7.0
ANALYSIS COMPUTATIONS
>>>>View Computation
Inputs
Channel Discharge(Q): 4.56 cfs
Peak Flow Period (H): hours
Channel Slope(S0): 0.0445 ft/ft
Bottom Width (B): 0 ft
Left Side Slope(ZL): 3 (H : V)
Right Side Slope(ZR): 5 (H : V)
Existing Channel Bend: No
Bend Coefficient(Kb): 1
Channel Bend Radius:
Retardance Class of Vegetation:C 6-12 in
Vegetation Type: Mix(Sod and Bunch)
Vegetation Density: Very Good 80-95%
Soil Type: Clay Loam (CL)
Channel Lining Options
DS75 Protection Type Temporary
S75BN Protection Type Temporary
S75 Protection Type Temporary
Basic Relationships
A= Cross sectional area, ft2(m2)=(B*D)+(ZL/ 2 * D2)+(ZR/2 * D2)
Where:
B = Base width of channel,ft(m)
D = Flow depth,ft(m)
ZL= Left side bank slope(H : 1 V)
ZR= Right side bank slope(H : 1 V)
P= Wetted perimeter,ft(m) = B +ZL* D +ZR* D
R=Hydraulic radius,ft(m)=A/P
V = Flow velocity,ft/s(m/s) = Q/A
Where:
Q = Channel discharge, cfs(cms)
Taua Average bed shear stress, psf(Pa) = 62.4* R*SO
Where:
SO = Gradient of channel,ft/ft(m/m)
Tauo= Maximum bed shear stress, psf(Pa) = 62.4* D*So
Unvegetated Conditions Computations:
n = Manning's n = a *Tauab
and (iteratively solved).
n = 1.486/Q*A* R(2/3)So°'S
Where:
n = Manning's n
https://ecmds.com/project/158279/channel-analysis/253246/calculations 1/3

2/16/24,9:29 AM ECMDS 7.0
a = Product specific coefficient from performance testing
b = Product specific coefficient from performance testing
SFr= Product factor of safety=Taur/Tauo
Where:
TauT= Permissible shear stress from testing, psf(Pa)
Taup= In place permissible shear, psf(Pa) =Taur/alpha * (Taus+ alpha/4.3)
Where:
alpha = unit conversion constant, 0.14 English, 6.5 Metric
Taus= Permissible shear stress of soil
SFL= Factor of safety of installed liner=Taup/Taua
Vegetated Computations:
n = Manning's n = alpha * Cn*Taua-0.4
and (iteratively solved).
n = 1.486/Q*A* R(2/3)So°5
Where:
alpha = Unit conversion constant, 0.213 English, 1.0 Metric
Cn =Vegetation retardance coefficient
SFr= Product factor of safety =Tauiv/Tauo
Where:
Tauw= Permissible shear stress from testing, psf(Pa)
Taup= In place permissible shear, psf(Pa) =Taus/(1 - CFTRM) * (n/ns)2
Where:
CFTRM= Coefficient of TRM performance derived from testing Taus= Permissible shear stress of soil
ns= Manning's of soil bed if left unprotected
SFL= Factor of safety of installed liner=Taup/Taua
S75
Predicted flow Cross sectional Wetted Hydraulic Flow velocity Froude Calculated Shear
Phase Mannings N SFP/SFL
depth(D) area(A) perimeter(P) radius(R) (V) number(FR) Stress
S75 Unvegetated 0.031 0.53 ft 1.13 ft2 4.39 ft 0.26 ft 4.04 ft/s 1.4 1.47 lbs/ft2 1.09(SFP)
Underlying 0.031 0.53 ft 1.13 ft2 4.39 ft 0.26 ft 4.04 ft/s 1.4 0.71 lbs/ft2 2.44(SFL)
Substrate
Unreinforced Vegetation
Predicted flow Cross sectional Wetted Hydraulic Flow velocity Froude Calculated Shear
Phase Mannings N SFP/SFL
depth(D) area(A) perimeter(P) radius(R) (V) number(FR) Stress
Unreinforced 0.05 0.63 ft 1.6 ft2 5.23 ft 0.31 ft 2.85 ft/s 0.9 1.76 lbs/ft2 2.28(SFL)
Vegetation
Underlying 0.05 0.63 ft 1.6 ft2 5.23 ft 0.31 ft 2.85 ft/s 0.9 0.85 lbs/ft2 4.7(SFL)
Substrate
S75BN
Predicted flow Cross sectional Wetted Hydraulic Flow velocity Froude Calculated Shear
Phase Mannings N SFP/SFL
depth(D) area(A) perimeter(P) radius(R) (V) number(FR) Stress
S75BN 0.031 0.53 ft 1.13 ft2 4.39 ft 0.26 ft 4.04 ft/s 1.4 1.47 lbs/ft2 1.09(SFP)
Unvegetated
Underlying 0.031 0.53 ft 1.13 ft2 4.39 ft 0.26 ft 4.04 ft/s 1.4 0.71 lbs/ft2 2.44(SFL)
Substrate
https://ecmds.com/project/158279/channel-analysis/253246/calculations 2/3

2/16/24,9:29 AM ECMDS 7.0
DS75
Predicted flow Cross sectional Wetted Hydraulic Flow velocity Froude Calculated Shear
Phase Mannings N SFP/SFL
depth(D) area(A) perimeter(P) radius(R) (V) number(FR) Stress
DS75 0.031 0.53 ft 1.13 ft2 4.39 ft 0.26 ft 4.04 ft/s 1.4 1.47 Ibs/ft2 1.09(SFP)
Unvegetated
Underlying 0.031 0.53 ft 1.13 ft2 4.39 ft 0.26 ft 4.04 ft/s 1.4 0.71 lbs/ft2 2.44(SFL)
Substrate
https://ecmds.com/project/158279/channel-analysis/253246/calculations 3/3

Channel Report
Hydraflow Express Extension for Autodesk®Civil 3D®by Autodesk, Inc. Friday, Feb 16 2024
Swale 02
Triangular Highlighted
Side Slopes (z:1) = 5.00, 3.00 Depth (ft) = 0.36
Total Depth (ft) = 1.00 Q (cfs) = 1.700
Area (sqft) = 0.52
Invert Elev (ft) = 689.97 Velocity (ft/s) = 3.28
Slope (%) = 4.55 Wetted Perim (ft) = 2.97
N-Value = 0.030 Crit Depth, Yc (ft) = 0.41
Top Width (ft) = 2.88
Calculations EGL (ft) = 0.53
Compute by: Known Q
Known Q (cfs) = 1.70
Elev (ft) Section Depth (ft)
691.00 1.03
690.50 0.53
v
690.00 0.03
689.50 -0.47
689.00 -0.97
0 1 2 3 4 5 6 7 8 9 10
Reach (ft)

29589.0000- Hidden Estates
Temporary Diversion Swale Calculations
2/16/2024
TDS-02
C i A Q TOP 689.97
(in/hr) (ac) (cfs) BOT 669.94
0.60 8.35 0.34 1.70 LENGTH 440
SLOPE 4.55%

2/16/24,9:29 AM ECMDS 7.0
NORTH North American Green
AMERICAN 5401 St. Wendel-Cynthiana Rd.
Poseyville, Indiana 47633
GREEN Tel. [phone]
>Fax [phone]
www.nagreen.com
ECMDS v7.0
CHANNEL ANALYSIS
>>>Swale 02
Name Swale 02
Discharge 1.7
Channel Slope 0.0455
Channel Bottom Width 0
Left Side Slope 5
Right Side Slope 3
Low Flow Liner
Retardence Class C 6-12 in
Vegetation Type Mix(Sod and Bunch)
Vegetation Density Very Good 80-95%
Soil Type Clay Loam(CL)
S75
Normal Permissible Calculated Safety Staple
Phase Reach Discharge Velocity Mannings N Remarks
Depth Shear Stress Shear Stress Factor Pattern
S75 Unvegetated Straight 1.7 cfs 3.08 ft/s 0.37 ft 0.033 1.6 lbs/ft2 1.05 lbs/ft2 1.52 STABLE D
Underlying Straight 1.7 cfs 3.08 ft/s 0.37 ft 0.033 1.74 lbs/ft2 0.51 lbs/ft2 3.42 STABLE D
Substrate
Unreinforced Vegetation
Normal Permissible Calculated Safety Staple
Phase Reach Discharge Velocity Mannings N Remarks
Depth Shear Stress Shear Stress Factor Pattern
Unreinforced Straight 1.7 cfs 2.05 ft/s 0.46 ft 0.057 4 Ibs/ft2 1.29 lbs/ft2 3.09 STABLE --
Vegetation
Underlying Straight 1.7 cfs 2.05 ft/s 0.46 ft 0.057 4 Ibs/ft2 0.63 lbs/ft2 6.39 STABLE --
Substrate
S75BN
Normal Permissible Calculated Safety Staple
Phase Reach Discharge Velocity Mannings N Remarks
Depth Shear Stress Shear Stress Factor Pattern
S75BN Straight 1.7 cfs 3.08 ft/s 0.37 ft 0.033 1.6 lbs/ft2 1.05 lbs/ft2 1.52 STABLE D
Unvegetated
Underlying Straight 1.7 cfs 3.08 ft/s 0.37 ft 0.033 1.74 lbs/ft2 0.51 lbs/ft2 3.42 STABLE D
Substrate
DS75
Normal Permissible Calculated Safety Staple
Phase Reach Discharge Velocity Mannings N Remarks
Depth Shear Stress Shear Stress Factor Pattern
DS75 Straight 1.7 cfs 3.08 ft/s 0.37 ft 0.033 1.6 lbs/ft2 1.05 lbs/ft2 1.52 STABLE D
Unvegetated
Underlying Straight 1.7 cfs 3.08 ft/s 0.37 ft 0.033 1.74 lbs/ft2 0.51 lbs/ft2 3.42 STABLE D
Substrate
https://ecmds.com/project/158279/channel-analysis/253247/show 1/2

2/16/24,9:29 AM ECMDS 7.0
https://ecmds.com/project/158279/channel-analysis/253247/show 2/2

2/16/24,9:30 AM ECMDS 7.0
NORTH North American Green
AMERICAN 5401 St. Wendel-Cynthiana Rd.
Poseyville, Indiana 47633
GREEN Tel. [phone]
>Fax [phone]
www.nagreen.com
ECMDS v7.0
ANALYSIS COMPUTATIONS
>>>>View Computation
Inputs
Channel Discharge(Q): 1.7 cfs
Peak Flow Period (H): hours
Channel Slope(S0): 0.0455 ft/ft
Bottom Width (B): 0 ft
Left Side Slope(ZL): 5 (H : V)
Right Side Slope(ZR): 3 (H : V)
Existing Channel Bend: No
Bend Coefficient(Kb): 1
Channel Bend Radius:
Retardance Class of Vegetation:C 6-12 in
Vegetation Type: Mix(Sod and Bunch)
Vegetation Density: Very Good 80-95%
Soil Type: Clay Loam (CL)
Channel Lining Options
DS75 Protection Type Temporary
S75BN Protection Type Temporary
S75 Protection Type Temporary
Basic Relationships
A= Cross sectional area, ft2(m2)=(B*D)+(ZL/ 2 * D2)+(ZR/2 * D2)
Where:
B = Base width of channel,ft(m)
D = Flow depth,ft(m)
ZL= Left side bank slope(H : 1 V)
ZR= Right side bank slope(H : 1 V)
P= Wetted perimeter,ft(m) = B +ZL* D +ZR* D
R=Hydraulic radius,ft(m)=A/P
V = Flow velocity,ft/s(m/s) = Q/A
Where:
Q = Channel discharge, cfs(cros)
Taua Average bed shear stress, psf(Pa) = 62.4* R*SO
Where:
SO = Gradient of channel,ft/ft(m/m)
Tauo= Maximum bed shear stress, psf(Pa) = 62.4* D*So
Unvegetated Conditions Computations:
n = Manning's n = a *Tauab
and (iteratively solved).
n = 1.486/Q*A* R(2/3)So°'S
Where:
n = Manning's n
https://ecmds.com/project/158279/channel-analysis/253247/calculations 1/3

2/16/24,9:30 AM ECMDS 7.0
a = Product specific coefficient from performance testing
b = Product specific coefficient from performance testing
SFr= Product factor of safety=Taur/Tauo
Where:
TauT= Permissible shear stress from testing, psf(Pa)
Taup= In place permissible shear, psf(Pa) =Taur/alpha * (Taus+ alpha/4.3)
Where:
alpha = unit conversion constant, 0.14 English, 6.5 Metric
Taus= Permissible shear stress of soil
SFL= Factor of safety of installed liner=Taup/Taua
Vegetated Computations:
n = Manning's n = alpha * Cn*Taua-0.4
and (iteratively solved).
n = 1.486/Q*A* R(2/3)So°5
Where:
alpha = Unit conversion constant, 0.213 English, 1.0 Metric
Cn =Vegetation retardance coefficient
SFr= Product factor of safety =Taurv/Tauo
Where:
Taurv= Permissible shear stress from testing, psf(Pa)
Taup= In place permissible shear, psf(Pa) =Taus/(1 - CFTRM) * (n/ns)2
Where:
CFTRM= Coefficient of TRM performance derived from testing Taus= Permissible shear stress of soil
ns= Manning's of soil bed if left unprotected
SFL= Factor of safety of installed liner=Taup/Taua
S75
Predicted flow Cross sectional Wetted Hydraulic Flow velocity Froude Calculated Shear
Phase Mannings N SFP/SFL
depth(D) area(A) perimeter(P) radius(R) (V) number(FR) Stress
575 Unvegetated 0.033 0.37 ft 0.55 ft2 3.07 ft 0.18 ft 3.08 ft/s 1.28 1.05 lbs/ft2 1.52(SFP)
Underlying 0.033 0.37 ft 0.55 ft2 3.07 ft 0.18 ft 3.08 ft/s 1.28 0.51 lbs/ft2 3.42(SFL)
Substrate
Unreinforced Vegetation
Predicted flow Cross sectional Wetted Hydraulic Flow velocity Froude Calculated Shear
Phase Mannings N SFP/SFL
depth(D) area(A) perimeter(P) radius(R) (V) number(FR) Stress
Unreinforced 0.057 0.46 ft 0.83 ft2 3.76 ft 0.22 ft 2.05 ft/s 0.77 1.29 lbs/ft2 3.09(SFL)
Vegetation
Underlying 0.057 0.46 ft 0.83 ft2 3.76 ft 0.22 ft 2.05 ft/s 0.77 0.63 lbs/ft2 6.39(SFL)
Substrate
S75BN
Predicted flow Cross sectional Wetted Hydraulic Flow velocity Froude Calculated Shear
Phase Mannings N SFP/SFL
depth(D) area(A) perimeter(P) radius(R) (V) number(FR) Stress
S75BN 0.033 0.37 ft 0.55 ft2 3.07 ft 0.18 ft 3.08 ft/s 1.28 1.05 lbs/ft2 1.52(SFP)
Unvegetated
Underlying 0.033 0.37 ft 0.55 ft2 3.07 ft 0.18 ft 3.08 ft/s 1.28 0.51 lbs/ft2 3.42(SFL)
Substrate
https://ecmds.com/project/158279/channel-analysis/253247/calculations 2/3

2/16/24,9:30 AM ECMDS 7.0
DS75
Predicted flow Cross sectional Wetted Hydraulic Flow velocity Froude Calculated Shear
Phase Mannings N SFP/SFL
depth(D) area(A) perimeter(P) radius(R) (V) number(FR) Stress
DS75 0.033 0.37 ft 0.55 ft2 3.07 ft 0.18 ft 3.08 ft/s 1.28 1.05 lbs/ft2 1.52(SFP)
Unvegetated
Underlying 0.033 0.37 ft 0.55 ft2 3.07 ft 0.18 ft 3.08 ft/s 1.28 0.51 lbs/ft2 3.42(SFL)
Substrate
https://ecmds.com/project/158279/channel-analysis/253247/calculations 3/3

EROSION CONTROL AND STORMWATER
CALCULATIONS
HIDDEN ESTATES
SECTION 2
RIP RAP OUTLET PROTECTION
29589.0000
ITI THOMAS Sc HUTTON

Rip Rap Apron Design
Project Name: 29589.0000 -Hidden Estates Outfall 2
Drainage Specialist: KSC Date: February 8, 2024
Checked By: NW Date: February 8, 2024
Step 1. Determine the tailwater depth from the channel characteristics below the pipe outlet for the
design capacity of the pipe. If the tailwater depth is less than half the outlet pipe diameter,it
is classifies as minimum tailwater conditions. If the tailwater is greater than half the pipe
diameter,it is classified as maximum tailwater conditions. Pipes that outlet onto wide flat
areas with no defined channel are assumed to have a minimum tailwater condition unless
reliable flood stage elevations show otherwise.
Rational Method for Flow
Total Drainage Area(Acres): 0.8
Outlet pipe diameter,Do(in.) 18
Tailwater depth(Feet) 0.5
Tailwater Method To Be Used Min TW(Fig.8.06a)
Discharge(cfs) 4.0
Velocity(ft./s) 2.3
Step 2. Based on the tailwater conditions determined in Step 1,enter Figure 8.06a or Figure 8.06b
and determine the d50 rip rap size and minimum apron length(La). The d50 size is the median
stone size in a well-graded rip rap apron.
Step 3. Determine the apron width at the pipe outlet,the apron shape, and the apron width at the
outlet end from the same figure used in Step 2.
Minimum TW Maximum TW
Riprap d50, (ft.) 0.3
Minimum apron length, La(ft.) ** 10
Apron width at pipe outlet(ft.) 5
Apron shape W=Do+La
Apron width at outlet end(ft.) 12
**-Minimum Apron Length Is 10 Feet per CLDS 20.23
Step 4. Determine the maximum Stone Diameter. D,,,aX= 1.5 X d50
Determine the Apron Thickness,Ta= 1.5 X dmax
Minimum TW Maximum TW
Max Stone Diameter, dmax (Inches): I 5
Apron Thickness(Inches): 10 gimmmilM1,
**-Minimum Apron Thickness Is 10 Inches per CLDS 20.23
Step 5. Fit the rip rap apron to the site by making it level for the minimum length La. Extend the
apron farther downstream and along the channel banks until stability is assured. Keep apron
as straight as possible and align it with the flow of the receiving stream. Make any necessary
alignment bends near the pipe outlet so that the entrance into the receiving stream is straight.
Some locations may require lining of the entire channel cross section to assure stability. It
may be necessary to increase the size of the rip rap where protection of the channel side
slopes is necessary. Where overfalls exist at pipe outlets or flows are excessive,a plunge pool
should be considered.

Figure 8.06a: Design of outlet protection from a round pipe flowing full, minimum
tailwater condition (Tw<0.5 diameter)
3Io
3
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diameter (Do) : •::: :: •y�.
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0
3 5 10 20 5'i 100 200 500 1000
Discharge (ft3tsec)
Curves may not be extrapolated.
Figure 8.06a Dosign of outlet protection protection from a round pipe flowing full, minimum tailwater condition (to<0.5 diameter)
Rev. 12'93 8.06.3

Rip Rap Apron Design
Project Name: 29589.0000 -Hidden Estates Outfall 5
Drainage Specialist: KSC Date: February 8, 2024
Checked By: NW Date: February 8, 2024
Step 1. Determine the tailwater depth from the channel characteristics below the pipe outlet for the
design capacity of the pipe. If the tailwater depth is less than half the outlet pipe diameter,it
is classifies as minimum tailwater conditions. If the tailwater is greater than half the pipe
diameter,it is classified as maximum tailwater conditions. Pipes that outlet onto wide flat
areas with no defined channel are assumed to have a minimum tailwater condition unless
reliable flood stage elevations show otherwise.
Rational Method for Flow
Total Drainage Area(Acres): 0.9
Outlet pipe diameter,Do(in.) 15
Tailwater depth(Feet) 0.5
Tailwater Method To Be Used Min TW(Fig.8.06a)
Discharge(cfs) 4.5
Velocity(ft./s) 3.7
Step 2. Based on the tailwater conditions determined in Step 1,enter Figure 8.06a or Figure 8.06b
and determine the d50 rip rap size and minimum apron length(La). The d50 size is the median
stone size in a well-graded rip rap apron.
Step 3. Determine the apron width at the pipe outlet,the apron shape, and the apron width at the
outlet end from the same figure used in Step 2.
Minimum TW Maximum TW
Riprap d50, (ft.) 0.3
Minimum apron length, La(ft.) ** 10
Apron width at pipe outlet(ft.) 4
Apron shape W=Do+La
Apron width at outlet end(ft.) 11
**-Minimum Apron Length Is 10 Feet per CLDS 20.23
Step 4. Determine the maximum Stone Diameter. D,,,aX= 1.5 X d50
Determine the Apron Thickness,Ta= 1.5 X dmax
Minimum TW Maximum TW
Max Stone Diameter, dmax (Inches): I 5
Apron Thickness(Inches): 10 gimmmilM1,
**-Minimum Apron Thickness Is 10 Inches per CLDS 20.23
Step 5. Fit the rip rap apron to the site by making it level for the minimum length La. Extend the
apron farther downstream and along the channel banks until stability is assured. Keep apron
as straight as possible and align it with the flow of the receiving stream. Make any necessary
alignment bends near the pipe outlet so that the entrance into the receiving stream is straight.
Some locations may require lining of the entire channel cross section to assure stability. It
may be necessary to increase the size of the rip rap where protection of the channel side
slopes is necessary. Where overfalls exist at pipe outlets or flows are excessive,a plunge pool
should be considered.

Figure 8.06a: Design of outlet protection from a round pipe flowing full, minimum
tailwater condition (Tw<0.5 diameter)
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Figure 8.06a Design of outlet protection protection from a round pipe flowing full, minimum tailwater condition (To<0.5 diameter)
Rev. 1:'93 8.06.3

EROSION CONTROL AND STORMWATER
CALCULATIONS
HIDDEN ESTATES
SECTION 3
HEC-22 STORMWATER ANALYSIS
29589.0000
ITI THOMAS Sc HUTTON

25-YR
CAPACITY

HEC-22
Storm Drain Computations
Structure ID Length Drainage Runoff Tc Rain"I" Runoff Known Q Total Q Pipe Full Q Velocity Velocity Invert Elevation Slope
(ft) Area Coeff"C" (min) (in/hr) "Q" (cfs) (cfs) Dia. (cfs) Full Design
From To (ac) (cfs) (in) (ft/s) (ft/s) U/S D/S
6 2 90 0.35 0.50 5 8.35 7.3 7.3 18 7.4 4.21 4.79 665.20 664.75 0.50%
1 6 15 1.38 0.50 5 8.35 5.8 5.8 18 37.0 20.96 15.25 667.00 665.20 12.41%
4 5 34_ 0.07 0.50 5 8.30 3.8 3.8 15 12.8 10.46 9.09 658.33 657.00 3.94%
3 4 67 0.84 0.50 5 8.35 3.5 3.5 15 9.7 7.88 7.25 659.83 658.33 2.24%
Ili THOMAS& HUTTON T:\AutoCADlReports\HEC-221HEC-22Reporting

HEC-22
Energy Grade Line Computations
Struct. Q EGLo HGLo Total Pipe EGLi HGLi Ea EGLa Surface Elev.
ID (cfs) (ft) (ft) Loss (ft) (ft) (ft) (ft) (ft)
(ft)
2 1 664.75 664.75 666.46
6 7.3 666.31 665.95 _ 0.45 666.76 666.40 1.8 667.02 670.32
1 5.8 667.09 666.92 671.01 667.40 4.0 671.01 668.71
5 _ 657.00 657.00 658.44
4 3.8 658.75 657.46 660.08 658.79 1.8 660.08 665.50
3 3.5 660.13 660.00 661.17 660.35 1.3 661.17 667.32
T'THOMAS& HUTTON T.•\AutoCAD\Reports\HEC-221HEC-22Reporting

4 IN/HR
INLET
SPREAD

H EC-22
Inlet Capacity Results
Structure Q=CIA/Kc Known Longitudinal Cross Cross Prey. Total Depth Gutter Spread Inlet Type Grate Grate Curb Curb Intercept Bypass Bypass Remark
(cfs) Q Slope Slope Slope Bypass Gutter d Width T Length Width Opening Opening Flow Flow Structure
(cfs) SL Sx Sw Flow Flow (ft) (ft) (ft) (in) (in) Length Height Qi Qb
(ft/ft) (ft/ft) (ft/ft) (cfs) (cfs) (in) (in) (cfs) (cfs)
6 1.5 0.08 0.10 1.5 0.1 2.0 3.0 Grate inlet 23.8 23.8 1.3 0.2
3
3.5 0.04 0.04 3.5 0.2 2.0 5.8 Grate inlet 23.8 23.8 2.1 14H
4 0.3 0.161 0.09 1.4 1.7 0.1 2.0 2.9 Grate inlet 23.8 23.8 1.4 0.31
TH THOMAS& HUTTON T:\AutoCAD\Reports\HEC-221HEC-22Reporting