Author(s): Jorge D. Bacchiega; Claudio A. Fattor
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Keywords: Energy dissipation; Local scour; Scour downstream of a dam
Abstract: One of the consequences of the construction of dams on rivers is related to the changes in the sediments transportation regime. The dam accelerates the sedimentation process in the reservoir and produces an increase of the erosion processes towards downstream. By this reason, some of the structures designed for a determined purpose can suffer a modification in its functioning. The present paper deals with a particular case of a dam located in Argentina. Los Quiroga deviation dam is located on River Dulce, 23 km from Santiago del Estero city, at the north area of the country, and its construction was finished around 50 years ago. The dam is 8.6 m high and the main function is to deviate water for irrigation purposes. The exceeding discharges are spilt by a 320 m-free wide low spillway with a hydraulic jump stilling basin for energy dissipation. This part of the structure was designed for the tail-water conditions existing at that moment. After 50 years of operation, the riverbed has decreased its elevation around 2.50m, and consequently the energy dissipation rate has been significantly reduced. The studies developed at the Hydraulics Laboratory of the National Institute of Water in order to define alternatives to get good energy dissipation conditions are presented here. A series of extensive analysis were made by means of a1:40 length scale two-dimensional physical model to make clear the reasons of the process and to evaluate possible solutions. Between the feasible alternatives to be implemented in the prototype, the most adequate scheme from the hydraulic viewpoint includes modification in the stilling basin (construction of baffle piers and the construction of a second slab immediately downstream of the existing slab), in order to get the energy dissipation of the residual energy at the exit section of the modified stilling basin.
Year: 2004