Analytical Solutions for Estimating Effective Discharge

Abstract

The concept of a dominant discharge that governs the cross-sectional and planform characteristics of a channel is used widely in stream restoration practice. This dominant discharge can be based on field measurements, a chosen recurrence interval of flooding or related to the effective discharge. The effective discharge is defined as the flow which transports the most sediment over the period of record. Significant differences in the relation between the computed effective discharge and bankfull discharge have been documented in the literature. Herein, different methods of estimating the effective discharge are described and analytical solutions derived. These analytical solutions are easy to apply and can be used to predict the effective discharge under existing conditions and the historic flow records. These solutions can be used to explain some of the discrepancies between different methods of estimating the effective discharge. In addition, the equations can be used to predict future trends in the effective discharge should the hydrologic, sediment transport or channel characteristics change in the future. The analysis procedures are illustrated with examples at two different scales: The Red River in Idaho and the Russian River in Northern California.