Scour Evaluation Program for Toe-Down Depth Assessment

An analysis procedure is presented to evaluate the bed scour potential along unlined drainage ways and watercourses for the purpose of determining toe-down depths for hydraulic structures. The stability and safety of drainage structures along watercourses are a major concern for many managing agencies as this involves potential lawsuits and costly operating losses. The methodology considers a number of components contributing to the total bed degradation in the channel that include the bend scour, local scour, general scour, low-flow incisement, long-term scour, and bed-form trough depths. Application of the proposed scour evaluation methodology is intended for alluvial watercourses in arid regions where streams are predominantly dry all year-round. A Windows-based program, coded in Visual Basic, was developed to compute each scour component by stage and ultimately evaluate the total bed scour. Data input for the program includes bed material data, flow hydraulics in the watercourse, and channel geomorphology. The flow hydraulics associated with the design and dominant flows can be imported directly from HEC-2 or HEC-RAS model outputs in which a reach-wide evaluation of scour is performed. The scour evaluation program has built-in sensitivity analysis for input data to assess the impact of these data on the scour values evaluated.