Scour downstream of aprons caused by sluices

Abstract

The characteristics of scour holes in uniform and nonuniform sediments downstream of an apron due to a submerged horizontal jet issuing from a sluice opening are studied experimentally. Attempts are made to explain the similarity existing in the scour profiles (including the dune downstream of the scour hole). From the scour profiles, the characteristic lengths of the scour hole which are determined are: horizontal distance of dune crest from the edge of the apron; dune height; horizontal distance of maximum scour depth from the edge of the apron; horizontal extension of scour hole from the edge of the apron and maximum equilibrium scour depth. For uniform sediments, the horizontal distance of the dune crest from the edge of the apron, the horizontal distance of maximum scour depth from the edge of the apron, the horizontal extension of scour hole from the edge of the apron and the maximum equilibrium scour depth were all found to increase with increase in densimetric Froude number; whereas the dune height decreases with increase in densimetric Froude number. In addition, for nonuniform sediments, the aforementioned characteristic lengths of the scour hole are related to the geometric standard deviation of sediments. The characteristic lengths of the scour hole decrease with an increase in geometric standard deviation of sediments. The application of the findings of the paper to the prototype is discussed, which would assist the practising civil engineer to ascertain the dimensions of a scour hole (scour depth, position of maximum scour depth, extension of scour hole etc.) in uniform and nonuniform sediments downstream of an apron. Importantly, these are the key parameters for designing apron foundations and protective measures for scour downstream of an apron. Future work will focus on field work to prove the scalability of the derived relationship.