Lognormal Distribution and Direct Runoff
Publication: Building Partnerships
Abstract
For design projects in the water resources area, a hydrograph of direct runoff curve is commonly used for the determination of the expected flood volume generated by a given drainage basin in response to a uniform rainstorm. The division of total flow into the direct runoff and the baseflow is of paramount importance for these type of studies. A large sample of natural hydrographs of total flow, chosen from different geographical areas of the 48 contiguous States, is considered for the study analysis in this investigation. These hydrograph curves are analyzed to divide the total flow into the direct runoff and the baseflow volumetric quantities, respectively. A two-parameter Lognormal Distribution is fitted to each one of the hydrographs of the direct runoff curves as obtained through the proposed analysis from these sample hydrographs of total flow. The two individual parameters of the Lognormal Distribution are related to the dimensionless shape factor and the storage time constant of the drainage basin, respectively. Both parameters are determined through the analysis of the total flow data as measured at a stream gaging station. The calibrated form of the two-parameter Lognormal Distribution, representing the direct runoff as the natural hydrograph curve, describes it rather well and furnishes accurate estimates of the flood volume of the computed direct runoff, as well as, provides a compatible length value of the hydrograph timebase and, of course, helps in the determination of the accurate profile of the corresponding baseflow curve for a given drainage basin under consideration.
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© 2000 American Society of Civil Engineers.
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Published online: Apr 26, 2012
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