Integration of Design Aids with TR-55 for Sediment and Stormwater Control

Rapid development and awareness of the problems associated with erosion and siltation are increasing the numbers of communities that adopt erosion control standards. Implementing these standards requires the ability to assess the effectiveness of proposed erosion control structures, thus a desirable technique is one that is relatively simple to implement, yet scientifically sound. The objective of this work was to develop a design and assessment method that would be easier to use than a complex sediment-routing model, be more accurate than commonly used rules of thumb, yet be conservative in those cases where it is not accurate. A large database of typical structures, impoundments, watersheds, and soils was assembled, and the SEDIMOT III model was used to find the trapping efficiency of each structure under varying inflow conditions. Regression models were then developed to predict the lower limit of trapping efficiency, given the overflow rate and soil properties. A separate set of soils data was used to test the algorithms, and they were found to reproduce the SEDIMOT III results. Models were developed for ponds with riser outlets, rock check dams, and rockfill outlet ponds. A technique for designing a sediment detention pond using the algorithms and the NRCS TR-55 model was developed. Two examples illustrating the technique are presented. The technique is being incorporated into the revised NRCS TR-55 model.