A Comparison of Techniques for Rainfall-Runoff Determination in a Small Watershed

Louisa Wildman, Oregon State University, OR, USA and Yunus Salami, LeTourneau University, TX, USA


Gauging devices for water discharge measurement are used to estimate flows in engineered and natural channels. Semi-empirical methods also exist that can be used to estimate overland rainfall excess that terminates in such channels. The reliability of these methods and correlations between them are important to be able to quantify runoff and make informed stormwater management decisions for both pre- and post-development conditions.

This study quantified runoff from a watershed whose main collection point is an onsite retention pond. Runoff measured empirically from various precipitation events was compared with runoff determined from other methods like the Curve Number method of the Soil Conservation Service. The effect of land use and magnitudes of precipitation events on both runoff volume and weighted runoff coefficient from the Rational method was also noted and reported.

Preliminary results appear to suggest that runoff determined from independent gauging devices agreed with theoretically determined runoff only for certain precipitation events. This could indicate that additional factors may need to be considered, for example, the antecedent moisture conditions of the watershed. Also, while runoff coefficients determined seemed to sometimes correlate with values expected for this land use type, additional research on similar-sized watersheds may be needed to understand instances where outliers were observed.

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