Runoff Generation in Western Washington as a Function of Precipitation and Watershed Characteristics

摘要

Twenty-nine watersheds of Western Washington are studied to establish relationships between precipitation and runoff as modified by physiographic characteristics. The relationships are studied using primary statistical parameters of the hydrologic series. It is established that the mean annual discharge and the mean annual hydrograph (using monthly sub-units) are highly correlated to watershed hypsometry. The standard deviation of annual discharge is shown to be generally predictable on the basis of precipitation data; it is also found to be a linear function of the mean annual discharge. Precipitation skewness and kurtosis are shown to be roughly defineable by geographic delineations. Runoff skewness is generally less than that of precipitation. Kurtosis of runoff is less easily defined but generally has a value of less than three. Annual precipitation appears to be serially correlated, and the correlogram of runoff is shown to be highly correlated to that of precipitation. Cross-correlations of precipitation and of runoff series are shown to be functions of proximity and of a directional component. Harmonic analyses of the runoff and precipitation series indicate strongly that cycles of approximately 16.5 and 5.5 years may exist. (WRSIC abstract)