EQUILIBRIUM SLOPE OF A “FLOOD PLAIN” IN AN EXPERIMENTAL CHANNEL, AS A FUNCTION OF DISCHARGE AND SAND SUPPLY

Abstract

A series of experiments was performed to determine the effect of water discharge and sand supply on the slope of a “flood plain” in an equilibrium state. A slope that was formed by deposition of uniform sands, 0.5_??_1.0 mm in diameter, was measured when the equi-librium state appeared in a sufficiently broad flume (57 cm) under a fixed condition of discharge and sand supply. Experiments were made on 23 combinations of discharge and sand supply (Table 1). Within the limits of our experiments, the slope is a linear function of sand supply and/or the ratio of sand supply to discharge when discharge is constant (Fig. 5). When the ratio of sand supply to discharge is constant, the relation between the slope and discharge is nearly linear on a log-log scale (Fig. 7). The ratio of sand discharge to sand supply was measured as a mark of the equilibrium state under the fixed condition. This ratio fluctuates randomly around the mean value 1.0 with time, even though operation time is longer than enough to appearance of the equilibrium state (Fig. 3). The equilibrium state, therefore, should be dealt with as a stochastic one determined by some semidependent variables, for example, velocity, depth and width of running water, roughness of sand bed, etc., which change spontaneously even under a fixed external condition.