Temporary Sediment Basin SD-3 Calculator (GSWCC)

February 22, 2026

This is a test version, and I would appreciate any comments and bug reports. This calculator implements the Temporary Sediment Basin (SD-3) sizing workflow from the Manual for Erosion and Sediment Control in Georgia and turns the Design Data Sheet into a repeatable, transparent set of computations.

Unlike “black box” tools, SD-3 depends heavily on table lookups and a few fixed criteria. The calculator keeps those steps visible by showing only the relevant window of each table and highlighting the exact cell(s) used for your design.

Temporary Sediment Basin (SD-3) Calculator

Temporary Sediment Basin SD-3 Calculator

Design workflow & spillway routing.

1. Hydrology & Area

Project NameFor export reference.Basin No.Must be between 1 and 50.

Drainage area (ac)Total watershed area.Disturbed area (ac)Disturbed drainage area.Peak Q2 (cfs)2-yr peak discharge.Peak Q25 (cfs)25-yr peak discharge.

2. Basin Geometry

Sediment storage depth (ft)Minimum 4 ft.Upstream side slope Zu (H:V)E.g., 3.0 = 3:1.Downstream side slope Zd (H:V)E.g., 4.0 = 4:1.

3. Elevations & Slopes

Top of dam elevation (ft)Existing/planned crest.Freeboard (ft)Added to DHW.Outlet pipe out elevation (ft)Lowest pipe elevation.Pipe elevation at riser (ft)Used to compute riser length.Entrance channel slope Se (%)Approaching channel slope.Exit channel slope So (%)Exit slope to compute Vo.

4. Spillway Specs

Pipe length measured (ft)Leave blank to calculate.Outlet pipe diameter overrideLeave Auto to auto-size.Pipe materialAffects anti-seep collar check.Orifice diameter (in)Dewatering time estimate.Design contingency (%)Optional contingency added to Vs.

Emergency spillway option

Results

Storage min (Vs)

351.1 cy

Clean-out (Vc)

115.3 cy

Surface area min

5310 sf(0.122 ac)

Principal Spillway

H=8.50 ft|L=71 ft|Dps=18 in|CF=1.00|Qps = 16.40cfs

Emergency Spillway

Qes: 1.70 cfs

Vo: 0.63 fps

Temporary Sediment Basin Cross-Sectional Detail