Methodologic criteria to modify existing dam stilling basins, to make them suitable for discharges bigger than original design flow

摘要

In order that ancient dams comply with the new security requirements demanded by the regulations in force, it is necessary to check them and to lay down general methodologic criteria. Based on this, the changes needed by these dams can be assessed and done so they function correctly with spillway flows bigger than original design flows. This paper is related to the stilling basins placed at the toe of gravity dam spillways where energy is dissipated by means of hydraulic jump. Some theoretical ideas are presented and they allow to plan the changes that have to be done to the stilling basin so it works correctly under the new flow conditions. These are: a predimensioning chart that makes easier the choice of the kind of stilling basin valid for a particular project according to the specific flow and the water level height upstream the spillway (crest elevation plus design head), and artificial aeration in the chute, inmediatly upstream of the dissipation structure, as a way to avoid cavitation and improve the hydraulic conditions at its entrance. Two examples are solved to clarify the ideas and reasonings presented.