Assessment of Kinematic Wave Time of Concentration

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Abstract
There is a need for an accurate limit for the practical use of the kinematic wave form of the St. Venant equations for computing the time of concentration for sheet flow. Such a limit will help ensure accurate designs for small watersheds. The current practice of limiting the flow length in the kinematic-wave time-of-concentration equation is problematic. This paper presents and analyzes limiting criteria, including L , iL , and nL S, where L is the overland flow length, i is the rainfall intensity, and S is the slope of the surface. Data reported in the literature from 59 actual and experimental watersheds are empirically analyzed. The criterion nL /S appears to be the best criterion, and it results in minimum standard errors of estimate when the upper limit of nL /S is 100 (English units). Theoretical routing using a range of basin slopes, roughness coefficients, and flow lengths gives an optimum limit on nL S of 80 (English system). Since the empirical analysis has a more direct relationship to the app...

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