Manning n and The Overland Flow Equation

MANNING n values for the over-land flow surfaces of a grassed watershed are derived by hydrograph analysis and by using average water-shed slope and overland flow length values determined by geomorphic methods. These values are compared with Manning n values from labora-tory tests on channels having similar grass covers. Close agreement was found for poor grass but not for fair and good grass. The methods can be used to estimate the overland flow equation for an ungaged water-shed if a Manning n value for the overland flow surface can be estimated.