Model Investigations of Stepped Spillway

Stepped block protection has considerable potential as a low-cost method for the construction of chute spillways and the protection of embankments from erosion by overtopping flow. Stepped spillways are structurally stable, resistant to water loads and significantly increase the rate of energy dissipation on the spillway face thus eliminating or greatly reducing the need for a large energy dissipation basin at the spillway toe. It can also be readily adopted for use in diversion works during dam construction and for providing additional spillway capacity to existing dams. While constructing stepped spillway over embankment dam, the stepped block is used in conjunction with an under layer which incorporates a free draining medium and a lower zone which has the function of filtering seepage flow out of the subsoil and also protecting the subsoil from erosion by flow in the draining layer. Blocks are laid in stretcher bond configuration. It is proposed to construct stepped precast concrete block spillway over the truncated embankment dam to be constructed at Jambhira in Orissa on Subarnarekha river. In the present study, model investigations are carried out to study the energy dissipation efficiency of the monolithic stepped spillway and the negative slope of the toe wall to be provided for the spillway. The stepped spillway is found to be very efficient in energy dissipation. It was observed that with the increase in discharge, the amount of energy dissipated is reducing. For additional energy dissipation, a toe wall with a negative slope of 8 to 12 is found to be suitable. o o