透過性砂防ダムの土石流調節機構

Abstract

Debris flow control becomes a major problem to prevent and to mitigate sedimenthazards these ten years. A large number of concrete dams, called sabo dams, have beenconstructed to reduce or to control sediment runoff from mountain regions. Most of themare filled up soon by sediment in the areas of active sediment yield, decreasing theirsediment storage capacities. Concrete dams, consequently, could not have controlled debrisflows successfully if they lose their storage capacities. Instead of them, grid dams, whichare some kinds of open dams, may be attractive as a sediment control work.In the present study, two types of grid dam, zigzag and square grid dams, are chosenfor considerations, to investigate the mechanisms of debris flow control. Flume tests aremade with attention focused on the relation among pass rates of sediment through griddam, sediment particle sizes and openning lengths of grids. A mathematical model whichgives a boundary condition at the dam is presented to evaluate the pass rate of sedimentthrough the dams.Numerical analyses are made with Asida and Egashira's governing equations of debrisflow for the outflowing sediment rate through the dams as well as the deposition of sedimentfrom the debris flows in the upstream reach of the dams. These simulated results comparewell with the data from flume tests.