Laboratory Investigation of Head loss in Gabion steeped spillways and Comparing with rigid stepped spillways

Stepped spillways are used in high dams, diversio dams and in watershed structures. Since gabion structures in many places is a good option, Gabion stepped spillways are being built with a height between 1 to 3 meters and these structures usually can be built with the same form. In this research compare the energy loss in gabion stepped spillways and rigid stepped spillways is done. To reach this goal, models of rigid stepped spillways and gabion stepped spillways was built with the same geometric dimensions and was installed in a laboratory flume with 50cm width and 11m length. Spillways have 1, 2 and 3 steps. Flow with different discharges was flowed in the flume. The results showed that the maximum efficiency of energy losses in the first case (one step) of rigid stepped spillways is 25/8%, the second case (two step) is 56/6% and the third case (three step) is 65/2%. Also the amount of maximum energy losses for the first case (one step) of gabion spillway is 49/9%, the second case (two step) is 71/3% and 73/5% for the third case (three step) respectively. This research showed that stepped gabion structures in the case of 2 and 3 steps have 16/9% and 16/3% (in average) efficiency of energy losses more than rigid structures. Also increasing the flow discharge, reduced the efficiency of energy losses. Further more increase the number of steps increases the energy losses. The effect of the second step in increasing the efficiency of energy losses was more than third step.