Iowa DOT In-Channel Sediment Control Basin Design Tool

A spreadsheet-based tool was developed to implement in-channel sediment basins and the various structural and components that enhanced sediment capture and turbidity reduction, as indicated through large-scale testing results.  The development of this tool provided design guidance for implementing in-channel sediment basins.  Users are prompted to input basin geometry and desired dewatering systems to determine detention volume and discharge characteristics and are provided with skimmer size selection, orifice diameter, plots of the channel cross-section at the earthen berm, stage-storage curve, and stage-discharge curve for design tables and reports.  Additionally, the tool includes a section to input a specific soil gradation to determine if flocculant should be applied.  Flocculant application is suggested if less than 80% of the sediment is predicted to settle within the desired dewatering time. 

The second portion of the tool allowed the user to select a dewatering system.  The user could toggle between a rock spillway, riser pipe, and skimmer.  Outputs from this portion of the tool included a stage-discharge curve.  The user may also input time and flow rate into available hydrograph parameters.  If the user elects to input a hydrograph, the tool relies on the Muskingum Routing method at 5 min (300 second) time steps to model the hydrological flow into and discharged from the basin.  This method considers the discharge capacity of the selected dewatering device.  When routing is utilized, the tool supplies users with a created storage indication curve used to predict discharge, an inflow and discharge hydrograph, and the basin’s volume over time to illustrate dewatering. 

The last portion of the tool allows the user to input a soil gradation from a combined sieve and hydrometer analysis.  Additionally, the tool allows the user to adjust the expected water temperature, starting with freezing, in the basin to adjust settling calculations.  If no temperature is selected, 70 °F (20 °C) is the default.  To predict settling, Stoke’s Law was applied to determine if a particular sediment particle size class would settle within the user-specified dewatering time.  If no dewatering time is specified, three days is considered the default.  The settling velocity for each particle size class was multiplied by the desired dewatering time to determine a settling distance.  If the settling distance was greater than the user-input spillway height, or maximum stage level, the particle size class was assumed to be settled.  If the settling distance was less than the spillway height, the particle size class was considered to be still suspended.  If more than 20% of all sediment was still considered to be suspended, flocculant application was recommended.