Overland Flow on Impervious Surfaces. July 1977.

Abstract

Shallow sheet flows both with and without rainfall are studied on smooth and rough surfaces. Theoretical studies describe mathematically laminar flow on rough surfaces and transition to turbulent flow on smooth surfaces, also describing the effect of rainfall on shallow flows. Experimentally, flows are studied on a smooth surface and two rough, one of uniform spheres and the other a typical road surface. Frictional factor, Reynolds numbers are derived for all surfaces and it is shown that a relative roughness effect exists in laminar flow. In turbulent flow, surface texture can be described by the Nikuradse sandgrain roughness height. The effect of rainfall is to increase flow resistance, the effect more marked at high rainfall rates and low Reynolds numbers. Experimentally, the road surface results yield a prediction equation which enable the road engineer to predict flow depth from rainfall rate and length and slope of the flow path. The results are compared with other studies of flow depth on road surfaces. Problems of measuring flow depth in shallow flows are discussed in detail and an instrument developed to to measure the mean water level of a distrubed water surface.