SW6231103_Erosion Control Calculations_20231121

CALCULATIONS
Sediment Basin Calculations
CE N C/Ns
CJ
EST. 10
yr
CAR

Project Data Revisions
Project# 2022-045 No Date Description
Project Name Godwin Subdivision
Date 10/25/2023
SEDIMENT SKIMMER BASIN
Sediment Basin#1
Sediment Basin# 1
Area Disturbed= 1102163 sf
25.30 acres
Peak Discharge Calculation:
Drainage Area= 1102163 sf
25.30 acres
Q10=C x I x A
C= 0.50
I o= 2.60 in/hr **55 minute Tc due to large drainage area
A= 25.30 acres
Quo= 32.89 cfs
Minimum Surface Area Calculation:
Surface Area(SF) =Q10x435 sf/ac
=32.89 cfs x435 sf/ac
Surface Area Req= 14308 sf
Basin Volume Calculation:
Volume of Sediment =(Drainage Ac.)x(1800 cfsed./year)x(1 year)
=25.3 ac x 1800 x 1 yr
Min Vol= 45544 cf
Assumed basin depth= 2 ft min D=2'for"Temp Sediment Basin"
Resultant Basin Area Req= 22772 sf
Check Surface Area Criteria
Surface Area Requirement= 14308 sf
Basin Volume Cale Area= 22772 sf
Therefore:Basin Volume Area Requirement Governs
Min Volume Req= 45544 cf
Min Area Req= 22772 sf
L:W Ratio= 2.5
Use L=2.5xW,calculate basin dimensions
Actual W= 96 ft Min W= 96 ft
L= 240 ft MinL= 240 ft
D= 2 ft
Actual Vol= 46080 cf Vol Check: OK
Actual Area= 23040 sf Area Check: OK
Actual Basin Dimensions= 96 ft W x 240 ft L x 2 ft D
Weir Design and Velocity Check:
Calculate Flow Depth H=[Q/CLf3
Q30= 32.89 cfs
C= 2.68 constant
L= 30 ft minL=10'
H= 0.55 ft max H=1'
Calculate Velocity Over Weir V=Q/A
V=32.89 cfs/30 ft x 0.55 ft
V= 1.99 ft/sec OK
Skimmer Sizing:
4 Skimmer Size(inches) Skimmer Size
0.333 Head on Skimmer(feet) (Inches)
3 Orifice Size(1/4 inch increments) 1.5
3.84 Dewatering Time(days) 2
2.5
3
4
5
6
8

Project Data Revisions
Project# 2022-045 No Date Description
Project Name Godwin Subdivision
Date 10/25/2023
SEDIMENT SKIMMER BASIN
Sediment Basin#2
Sediment Basin# 2
Area Disturbed= 150740 sf
3.46 acres
Peak Discharge Calculation:
Drainage Area= 150740 sf
3.46 acres
Q10=C x I x A
C= 0.50
ha= 7.2 in/hr 5 minute Tc
A= 3.46 acres
Quo= 12.46 cfs
Minimum Surface Area Calculation:
Surface Area(SF) =Q10x435 sf/ac
=12.46 cfs x 435 sf/ac
Surface Area Req= 5419 sf
Basin Volume Calculation:
Volume of Sediment =(Drainage Ac.)x(1800 cf sed./year)x(1 year)
=3.46 ac x 1800 x 1 yr
Min Vol= 6229 cf
Assumed basin depth= 2 ft min D=2'for"Temp Sediment Trap"
Resultant Basin Area Req= 3114 sf
Check Surface Area Criteria
Surface Area Requirement= 5419 sf
Basin Volume Calc Area= 3114 sf
Therefore:Surface Area Governs
Min Volume Req= 6229 cf
Min Area Req= 5419 sf
L:W Ratio= 2.5
Use L=2.5xW,calculate basin dimensions
Actual W= 47 ft Min W= 47 ft
L= 117.5 ft Min L= 118 ft
D= 2 ft
Actual Vol= 11045 cf Vol Check: OK
Actual Area= 5523 sf Area Check: OK
Actual Basin Dimensions= 47 ft W x 117.5 ft L x 2 ft D
Weir Design and Velocity Check:
Calculate Flow Depth H=[Q/CL]z"
Qio= 12.46 cfs
C= 2.68 constant
L= 20 ft minL=10'
H= 0.38 ft max H=1'
Calculate Velocity Over Weir V=Q/A
V=12.46 cfs/20 ft x 0.38 ft
V= 1.65 ft/sec OK
Skimmer Sizing:
2.5 Skimmer Size(inches) Skimmer Size
0.208 Head on Skimmer(feet) (Inches)
1.75 Orifice Size(1/4 inch increments) 1.5
3.42 Dewatering Time(days) 2
2.5
3
4
5
6
8