Transforms for Runoff and Sediment Transport

Abstract

Transforms reduce the distributions of surface-runoff and sediment-transport variables to near-exponential distributions typical of rainfall duration and intensity. Two transform parameters are determined from field measurements using either a graphical method or the method of moments. The transforms were tested on both small experimental plots and very large watersheds for the distributions of rainfall depth, runoff volume and discharge, sediment concentration and sediment discharge, as well as concentration and transport of chemicals from surface runoff. As expected from deterministic relationships, the inverse transform exponent $\stackrel{\mathit{ˆ}}{\mathit{b}}$ for point rainfall is close to unity, increases to about 1.5 for runoff discharge, and varies between 1.5 and 3 for sediment and chemical transport. Several examples show that the transforms are useful to determine exceedance probability, flow and sediment duration curves, expected sediment load, and sediment-rating curves for poorly correlated concentration and discharge measurements.