Urban Storm Runoff Inlet Hydrograph Study Volume 2; Laboratory Studies of the Resistance Coefficient for Sheet Flow over Natural Turf Surfaces

The main objective of this study is to develop an accurate design method for computing inlet hydrogaphs of surface runoff, with average recurrence intervals of 10, 25, and 50 years, from typical urban highway by flood routing technique. Resistance to sheet flows over natural turf surfaces is experimentally investigated. The formuation of a functional relationship between the resistence coefficient and controlling parameters for shallow flows over various turf surfaces is essential to the mathematical modeling of surface runoff from urban highway sideslopes covered with different species of turf. An analysis of results obtained from laboratory experiments from laminar flow on Kentucky Blue grass and Bermuda grass reveals that a relationship exists between the Darcy-Weisback friction coefficient, Reynolds number, and bed slope. Time did not premit tests to be performed on all species of turf other than Kentucky Blue grass and Bermuda grass which can be sodded. However, a general trend of the resistance relationship for shallow flows over such dense turf surfaces as affected by raindrop impact and roughness is qualitatively determined