SW6240205_Design Calculations_20240718 (3)

July 25, 2023
Sedimentation and Erosion Control Narrative Hoke County High School, Raeford, NC
Velocity Dissipater Design (For Flume Outlets)
Velocity Dissipater- 8
Drainage Area = 0.71 Acres
Flume Width = 2.0 ft
Flume Height= 0.50 Inches
(From Rainfall Intensity/Frequency Chart, Table 8.03c)
A_Impervious= 28452
C_Impervious= 0.9
A_Open = 2645
C_Open = 0.3
A_Total = 31097
C_Compose = (A_Imp x C_Imp+A_Open x C_Open)/(A_Total) = 0.85
C I A
Cho = CIA = 0.85 7.96 0.71 = 4.80 ft3/s
(runoff from open areas and parking) ("I" value obtained from the Erosion and Sediment
Control Planning and Design Manual, pg. 8.03.9)
Velocity, V=Q/A= 4.80 / 1.00 = 4.80 I ft/s
Zone = 1 (Erosion and Sediment Control Planning and Design Manual,figure 8.06.b.1)
Apron Material = Class A 'Stone Filling
Fine 3 1 Inch Diameter Stone
Depth of Stone = 12 Inches
Length of Apron, La = (x)(Do) = 4 1.0 = 4 ft
Use 4 ft
Width, Wi= (x)(Do) =f 2 1.0 = 2 ft
Use 3 ft
Apron Width Downstream, W2 = (x)(Do) + L=
1 1.0 + 4.0 = 5 ft
Use 5 ft
Note: Resultant values are minimum required. Plan may show larger sizes.
gawford
ue li Company
Rom,
Project#22026 Page 14 of 16

July 25, 2023
Sedimentation and Erosion Control Narrative Hoke County High School, Raeford, NC
Velocity Dissipater Design (For Flume Outlets)
Velocity Dissipater- 9
Drainage Area = 0.71 Acres
Flume Width = 2.0 ft
Flume Height= 0.50 Inches
(From Rainfall Intensity/Frequency Chart, Table 8.03c)
A_Impervious= 25744
C_Impervious= 0.9
A_Open = 5509
C_Open = 0.3
A_Total = 31253
C_Compose = (A_Imp x C_Imp+A_Open x C_Open)/(A_Total) = 0.79
C I A
Cho = CIA = 0.79 7.96 0.71 = 4.49 ft3/s
(runoff from open areas and parking) ("I" value obtained from the Erosion and Sediment
Control Planning and Design Manual, pg. 8.03.9)
Velocity, V=Q/A= 4.49 / 1.00 = 4.49 I ft/s
Zone = 1 (Erosion and Sediment Control Planning and Design Manual,figure 8.06.b.1)
Apron Material = Class A 'Stone Filling
Fine 3 1 Inch Diameter Stone
Depth of Stone = 12 Inches
Length of Apron, La = (x)(Do) = 4 1.0 = 4 ft
Use 4 ft
Width, Wi= (x)(Do) =f 2 1.0 = 2 ft
Use 3 ft
Apron Width Downstream, W2 = (x)(Do) + L=
1 1.0 + 4.0 = 5 ft
Use 5 ft
Note: Resultant values are minimum required. Plan may show larger sizes.
gawford
ue li Company
Rom,
Project#22026 Page 15 of 16

Hoke County High School Raeford, NC
Velocity Dissipator- 10
Drainage Area = 0.75 Acres
(From Rainfall Intensity/Frequency Chart, Table 8.03c)
A_Impervious= 0
C_Impervious= 0.9
A_Open = 32670
C_Open = 0.3
A_Total = 32670
C_Compose = (A_Imp x C_Imp+A_Open x C_Open)/(A_Total) = 0.30
C 1
Qlo = CIA = 0.30 7.96 0.75 = 1.79 ft3/s
(runoff from open areas and parking) ("I" value obtained from the Erosion and Sediment
Control Planning and Design Manual, pg. 8.03.9)
Velocity, V=Q/A= 2.18 ft/s from swale caculation
Zone = 1 (Erosion and Sediment Control Planning and Design Manual,figure 8.06.b.1)
Apron Material = Class A Stone Filling
r- Fine 3 Inch Diameter Stone
Depth of Stone = 12 Inches
Length of Apron, L2 = (x)(Do) = 4 2.5 = 10 ft
Use 12 ft
Width, Wi= (x)(Do) =E 2 2.0 = 4 ft
Use 4 ft
Apron Width Downstream, W2 = (x)(Do) + L=
1 2.0 + 4.8 = 7 ft
Use 10 ft
gawford
ue Company
Rom,
Project#22026 Page 1 of 1

Sedimentation and Erosion Control Narrative Hoke County High School Raeford, NC
Velocity Dissipater Design (For Pipe& Flared End Sections)
Velocity Dissipater- 11
Pipe Diameter, Do= 12 Inches = 1.0 ft
Flow Rate, Qio= 3.01 ft3/s
Velocity, V= 5.53 ft/s
Zone = 1 (Erosion and Sediment Control Planning and Design Manual,figure 8.06.c)
Apron Material = Class A Stone Filling
Fine 3 Inch Diameter Stone
Depth of Stone = 12 Inches
Length of Apron, L2 = (x)(Do) = 4 I 1.0 = 4 ft
L Use 4 ft
Width, Li = (x)(Do) = I 3 1.0 = 3 ft
Use 12 ft
Apron Width Downstream, W2 = (x)(Do) + L=
3 1.0 + 4.0 = 7 ft
Use 10 ft
gawford
ue Company
Rom,
Project#22026 Page 1 of 1