IMPROVED BANKFULL HYDRAULIC GEOMETRY PREDICTION USING 2-YEAR RECURRENCE INTERVAL DISCHARGE

Author

Laien He, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2011

Degree Name

Master of Science

Department

Civil Engineering

First Advisor

Wilkerson, Gregory

Abstract

Bankfull hydraulic characteristics, i.e., bankfull discharge (Q_bf), bankfull width (W_bf), bankfull mean depth (D_bf), and bankfull cross-section area (A_bf) are important design factors in stream restoration projects. Regional curves are widely accepted as a useful tool for estimating bankfull hydraulic characteristics at ungaged sites. Nevertheless regional curves are developed using only one independent variable, drainage area (A_da), to predict Q_bf and bankfull hydraulic geometry (W_bf, D_bf, and A_bf). Wilkerson (2008) has demonstrated that regression equations for predicting Q_bf can be improved by including the two-year recurrence interval flood flow (Q₂) as an explanatory variable. This paper explores the potential for improving predictions of bankfull hydraulic geometry by using Q₂ as an independent variable in regression models. For this study, bankfull hydraulic geometry data, and A_da and Q₂ estimates were obtained for 29 hydrologic regions (regions with similar hydrology or peak flow response) across 14 states. The data span a wide range of geologic, hydrologic, and climatic conditions. By comparing statistical measures (root mean squared error, coefficient of determination, and Akaike's information criterion), we determined that Q₂ has significant utility for improving predictions of bankfull hydraulic geometry. Without considering dataset size and compared to A_da, Q₂ is shown to be a better predictor of W_bf, D_bf, and A_bf, respectively, in 71%, 54%, and 64% of the cases we evaluated. When minimum dataset size requirements are set, these numbers increase.