Secondary depressed apron for scour reduction downstream of diversion barrages

River diversion barrages are subjected to varying hydraulic conditions ranging from gate controlled and uncontrolled flows with possible free and submerged conditions on the downstream. The resulting scour of the downstream riverbed material, varying according to the specific combination of the hydraulic parameters, may be reduced by providing a depressed apron on the downstream of the usual stilling basin. This paper investigates the possible shapes that may be given to the normal block protection apron downstream of a barrage structure that may best reduce the extent of downstream scour. The effectiveness of this secondary apron in preventing the hydraulic jump from moving dangerously out of the stilling basin for exceptionally low tail water conditions is investigated.