Guidelines for Assigning Erodibility Parameters to Soil Horizons for SITES analyses

Content & Objectives: The SITES computer program provides engineers with a tool for predicting the formation and progression of a headcut in an auxiliary spillway during a design storm.  The predicted performance given by SITES includes the extent and speed of development of a headcut that may develop in the auxiliary spillway.   The predicted erosion in the spillway depends on (1) the duration and quantity of design flow through the spillway during the design storm (design hydrograph) and (2) the erodibility parameters of the soil and bedrock horizons in the spillway model. 

The erodibility factors used in SITES are the headcut erodibility index Kh and the detachment rate coefficient, kd.  This Webinar provides guidance primarily on selection of Kh and kd parameters for soils.  Soils are vastly more erodible than bedrock and the erosion potential of soil horizons is extremely important in the predicted performance of any spillway that is not situated solely on bedrock.  The Webinar does not provide specific training on the actual use of the computer program SITES.  The training in the Webinar is confined to guidance related to the selection of the two erodibility factors for soil.  Bedrock is not explicitly included in the Webinar training, but some of the same principles in selecting the Kh and kd parameters for soils also apply to bedrock materials.  Information is extracted from NRCS publications on the SITES program as well as supplemental guidance developed by the Webinar trainer, Mr. McCook.