Basic Principles for Designing Backup Spillway with Eroded Insert

Based on the experience accumulated to date in the use of backup spillways with eroded soil inserts and previously conducted studies, recommendations for the design and calculations of such structures are given. Four options for design and layout solutions are presented. The first option is that the eroded insert is located in the body of the earth dam. The erosion-limiting clothing is concrete. The second option is the same, but the erosion-limiting clothing is made of soft polymer material, for example, from geotextile or polymer film. According to the third option, the eroded insert is located in one or several spans of the surface spillway and operates like a “Hydroplus” gate. The fourth option is applicable under appropriate topographic conditions. Here, the eroded insert is located outside the pressure front, bypassing the dam and is a small eroded dam. A procedure for hydraulic calculations is proposed, which are performed in two stages. At the first stage, the dimensions of the spillway opening of the reserve spillway are determined to allow the design flow to pass through. Then, a calculation is made of the erosion of the soil insert located in this hole, which occurs when water overflows over its crest in an emergency. This calculation makes it possible to determine the time of erosion, as well as to construct a hydrograph of water flow through the eroded spillway, graphs of changes in the level of the headwaters and the marks of the crest of the insert during the erosion process. It is convenient to solve differential equations that describe the erosion process using a numerical method. A calculation algorithm is proposed.