scaling relationships for local scour downstream of stilling basins

Farhoudi, Javad (1979) scaling relationships for local scour downstream of stilling basins. University of Southampton, Doctoral Thesis.

Abstract

An experimental investigation was made of local scour downstream of a hydraulic jump type stilling basin, which was reproduced in three different sizes each twice the other. The bed materials used were sand and granulated bakelite, the sizes ranging from 0.85 mm to 0.15 mm. A study was made of the similarity of scour evolution downstream of the stilling basin, the time scale of scour development, and the effect of scour development on the momentum balance of the jump. The dimensionless shape of the scour hole could be definedby a general equation, which also corresponded to observations by other investigators. Starting from the approach used by Breusers in connection with modelling scales for protective aprons for estuary closure structures, the Einstein-Brown bed-load formula has been adapted to find a relationship for the time scale of local scour downstream of a stilling basin. The time scale relationship, together with knowledge of the geometry of the scour hole, enables an equation to be written for determining scour downstream of structures geometrically similar to the model. Alternatively, the time scale relationship can be used as a model-prototype scaling relationship for investigations on similar basins with different geometrical configuration. The time scale relationship has been compared with two other possible methods for predicting the time scale of local scour. Included in the appendices are some relevant computer programmes and a numerical example which demonstrates the practical application of the derived results.

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