Improving runoff risk estimates: Formulating runoff as a bivariate process using the SCS curve number method

The Soil Conservation Service curve number (SCS-CN) method is widely used to predict storm runoff for hydraulic design purposes, such as sizing culverts and detention basins. As traditionally used, the probability of calculated runoff is equated to the probability of the causative rainfall event, an...

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Bibliographic Details
Published in:	Water resources research 2009-03, Vol.45 (3), p.W03404-n/a
Main Authors:	Shaw, Stephen B, Walter, M. Todd
Format:	Article
Language:	eng
Subjects:	base flow Catchment curve number engineering design Floods Freshwater hydrologic models Hydrology joint probability probabilistic models rain risk assessment runoff soil conservation soil water content storm runoff stream flow Uncertainty assessment Ungaged basins watershed hydrology
Online Access:	Get full text
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Summary:	The Soil Conservation Service curve number (SCS-CN) method is widely used to predict storm runoff for hydraulic design purposes, such as sizing culverts and detention basins. As traditionally used, the probability of calculated runoff is equated to the probability of the causative rainfall event, an assumption that fails to account for the influence of variations in soil moisture on runoff generation. We propose a modification to the SCS-CN method that explicitly incorporates rainfall return periods and the frequency of different soil moisture states to quantify storm runoff risks. Soil moisture status is assumed to be correlated to stream base flow. Fundamentally, this approach treats runoff as the outcome of a bivariate process instead of dictating a 1:1 relationship between causative rainfall and resulting runoff volumes. Using data from the Fall Creek watershed in western New York and the headwaters of the French Broad River in the mountains of North Carolina, we show that our modified SCS-CN method improves frequency discharge predictions in medium-sized watersheds in the eastern United States in comparison to the traditional application of the method.
ISSN:	0043-1397 1944-7973