Design of erosion protection at diversion tunnel outlets with concrete prisms

Abstract

Concrete prisms obtained by dividing cubes diagonally have been used successfully in some dam projects in Iran as a flexible and economical erosion protection measure at diversion tunnel outlets ending in a mobile river bed. To establish appropriate design criteria for this new protection measure, systematic hydraulic model tests have been performed. The physical tests allowed us to highlight the performance of the concrete prisms placed at a diversion tunnel outlet compared with an unprotected erodable riverbed. The concrete prisms are placed in such a way that in case of undermining, the protection system is able to deform and limit erosion and scour by always covering most of the river bed at the outlet. Based on the tests results, general applicable design criteria and equations, for estimating the scour hole geometry, its location, and the required size of the prisms as well as the total area to be protected, have been developed.Key words: diversion tunnel, scour, erosion protection, hydraulic model tests, concrete prisms, river diversion.