Application of dye tracing on sheet flow and determination of mean texture depth on a rough surface

A flume surface covered with sand grains of around 2 mm diameter was created to imitate the roadway surface of a highway. Rainfall and water flow was simulated over the surface which was elevated on one side to create slopes of 1%, 2%, and 3%. Mean texture depth was proposed such that water depth has to be greater than the mean texture depth to establish significant flow on a rough surface. Two methods were used to determine the mean texture depth. The first method involved fitting discharge and depth measurements to a model equation to determine the mean texture depth which was found to exist and it varied from 2.012 to 5.651 mm in "no rain" condition and from 1.580 to 5.348 mm in "rain" condition. The second method was to measure the discharge rate using dye tracing method. However, this method proved to be less successful. The mean texture depth determined by this method was negative in some conditions. The sink effect at the water collecting slots and the error of slot width measurements were investigated as potential source of error.