STUDY ON THE PERFORMANCE OF LAUNCHING APRON AROUND SOLID SPURS IN ALLUVIAL STREAMS

Abstract

Spurs-solid and permeable, are invariably provided. for river training works in alluvial streams. The flow gets modified in the presence of these spurs as a result scour develops at their nose. Design of spur a part from other parameters requires correct estimation, of this scour depth and measures to ensure its safety against this scour. Generally a launching apron consisting of suitable size of coarse material and thickness is provided around spur to provide a desired safety against scour. In present literature considerable information is available for estimation of scour depth and for the design of launching apron. However, very scanty information is available about the performance of launching apron as far as its behavior under increased discharges is concerned modification in the flow and bed geometry that it is likely to produce downstream of spur with this objective the present experimental investigation concerning above aspects of launching aprons has been taken up. The data using solid spur inclined at three different angles that is 600, 900 and 120° and using to different bed materials have been collected with and without launching apron. The results of velocity profiles in presence of scour hole developed around spur show that there is increase in local velocity in presence of scour hole. Further in presence of launching apron, scour shifts downstream of spur. The data collected in present study have also been used to check the adequacy of Melville's equation, which indicates that this equation can be used for scour predication at spur. Even though it is developed for abutments. Suggestions for future study have also been made.