Model Studies of Semi-Permeable Rubble Mound Weirs: Fid-Bau Portal

Model Studies of Semi-Permeable Rubble Mound Weirs

Lim, Yeo Howe / Fuqua, Jeffery

In recent years projects with various designs have attempted to sever formations of rollers downstream of low-head dams. One of the popular options is by dumping some rock materials at the toe of the dam, essentially creating a rubble mound with a sloping downstream face. It is widely perceived that the permeable rubble mound can break up the roller formation. The hydraulic conveyance of the combination of a solid impermeable weir and a permeable rubble mound has been ill defined. In pursuit of greater knowledge about the specific combination design, a research project sponsored by the North Dakota State Water Commission was conducted with the aim of developing a generalized analytical tool for this type of weir, considering the loss of conveyance and modifications options. Several scaled models were constructed and tested up to the limits of available laboratory environments. It was concluded that the addition of different types of rock wedges exerted some influence on the discharge over the weir although the conveyance at upstream positions is not discernible. Experimental results indicated that the ratio of head to the rock wedge length has different influences on the Froude number at the approach. The results also show an optimal ratio of rock wedge surface length to dam height is about 1.75. As expected, the addition of a rock wedge dissipates a large amount of energy, changes the location of the jump, and calms down the jump. This study also reconfirmed the main effect of the addition of a rock wedge as the removal or the minimization of the stationary roller.