Experimental Investigation of Energy Dissipation over Stepped-Labyrinth Weirs

Flow water passing through spillways of dams has a high level of kinetic energy, which can lead to extensive damage to downstream facilities and bring about severe erosion of river beds. Energy dissipation would usually be accomplished by creating structures such as still basins at downstream of weirs, flip buckets, or steps in weirs. Stepped spillways are one of the common structures for energy dissipation, as well as reduction of the dimensions of still basins. The effects of labyrinths on total energy dissipation at downstream of the stepped spillways with slopes of 1:1, 1:2 and 1:3 was investigated; the height of labyrinths was 0.5 and 0.75 of the height of steps (h), working interspaces were equal to two times of the height of steps, and three roughness heights on the step face were 0.002, 0.004 and 0.006 m. The results showed that in first case, 1:1 slope of the stepped spillway, a labyrinth with height of 0.5h, working interspaces of 2h and equal length of the steps caused an increase of 12.7 percent in dissipation of relative energy. The comparison of results showed that for slope of stepped weir of 1:2, installation of a labyrinth with a height of 0.75h, interspaces of 2h and equal length to the height of the steps, the relative energy dissipation increased by 8.4 percent. When stepped weirs with slopes equal to1:3 were used, results indicated that installation sill with a length h, a height of 0.5h instead of labyrinths on steps, caused an increase of 4.7 percent in relative energy dissipation. Result showed that increase surface roughness of studied weirs reduced the relative energy dissipation by 3.6 percent.