An Experimental Study on the Resistance Law of Rain Water Flow over a Slope Surface

Abstract

An experimental study was made of the flow regimes of shallow water over the slope of a smooth surface, an uneven surface, an artificial turf and a gravel layer under a constant rate of rainfall or inflow. The results are summarized as follows:
1) The flow along a partial water path on a smooth surface is a laminar flow. However, if the water depth of the flow is evaluated by the equivalent depth all over the slope, the flow is regarded as a turbulent flow.
2) The flow over an uneven surface is also a laminar flow. But this flow may be regarded as a turbulent flow for the effective depth whieh is evaluated by subtraction of depression and/or wedge storage from the actual depth.
3) The high flow over a turf surface is a laminar flow, but the Darcy law is applicable to a low flow lower than the height of the turf and the Manning law to the exceeded flow over the top of the turf.
4) The flow in a gravel layer is also regarded as a Darcy flow.
5) The effect of depression and/or wedge storage must be taken in consideration for the analysis of runoff from a slope surface, except the case of a smooth surfac.