Stand-by spillways in phreatic dams

Abstract

Hydraulic structures operation is always connected with accident risks. The authors analyzed emergency situations which affected dams located on the territory of the USA and Russia. This analysis showed that the most dangerous accident which took place at hydroelectric complexes is an overfall through the crest of the dam accompanied with the formation of washouts and blow-out waves. The most striking example here is the accident at St. Francis dam. According to most researchers, its main cause was the human factor. To reduce economic losses which are due to an accident on the hydro-technical construction and to reduce the risk of human influence, the authors propose to use a stand-by spillway in the body of a phreatic dam. For this purpose, they introduce two constructions. The first construction has a melting insert and a spillway channel fastening made of synthetic materials. The second one has filtering covering of a crest and a downstream slope made of coarse-pored concrete. The researchers perform physical and numerical modeling of the developed structures to compare them. On the basis of laboratory experiments and calculations in the program complex, they obtain discharge coefficient values for various spillways, which can be later used for calculating spillway capacity as well as for its construction.