DEBRIS FLOW CONTROL BY USING SLIT DAMS

Slit dams have been shown to be effective in trapping coarse sediment and retarding the debris flow. It is necessary to establish the controlling efficiency and the systematic procedures for designing slit dams, as well as reasonable sites for their location. Using the principle of mass conservation and laboratory experiments, this paper develops the sediment flow-out ratio and sediment concentration ratio to evaluate the effectiveness of the slit dam, and confirms that sediment concentration ratio increases with an increase in relative spacing and slit density. The sediment flow-out ratio depends on the sediment concentration ratio and sediment concentration before passing through a slit dam. For sediment concentration before passing through a slit dam, based upon Bagnold's concept of the dispersive stress generated by grain collisions in flow and bed shear stress, a semi-empirical relationship is obtained. Compared with other researchers' studies, this study is found to be in excellent conformity with theirs, when taking 0.1 as the empirical coefficient. Besides, height, spacing and location factors affecting a slit dam design for debris flow mitigation are established herein. Furthermore, the design procedures of a slit dam are provided as a useful tool for controlling the debris flow hazards and are illustrated by a numerical example.