Laboratory Analysis of Energy Losses in Gabion Steeped Spillways With and Without Sedimentation at Upstream

Energy losses in steeped spillways is one of the most important design parameters in this structure. Stepped spillways are used in high dams, diversio dams and in watershed structures. Gabion stepped spillways are usually used in diversion dams and structures of river protection. They are used in most projects, Specially in projects of stabilizing river and filling with sediment at upstream is one of the goals. 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. Therefore this form of gabion in the early years are filled with sediment. In this research compare the energy losses in two form of gabions stepped spillways (gabions stepped spillways with and without sedimentation at upstream) is done. To reach this goal, models of gabion stepped spillways with and without sedimentation were built with the same geometric dimensions and were installed in a laboratory flume with 50cm width and 11m length. Spillways have 1, 2 and 3 steps. The result showed that the maximum efficiency of energy loss in the gabion stepped spillways without sedimentation, occur up to 75%. At low flow rates, in the gabion without sedimentation flow traverses through the porous body. In this mood, when discharge increases the energy losses will increase too, but in the flow passing through and upper gabion, energy losses will be reduced. In gabion stepped spillways with sedimentation, increasing flow always makes reduce energy losses. When current passes through the porous body, in gabion without sediment energy losses is less than gabion with sediment. But when current passes from the top of gabion, in gabion without sediment energy losses is more than gabion with sediment. This study present three formulas for calculating energy losses in Gabion stepped spillways.