Development and Evaluation of Bankfull Hydraulic Geometry Relationships for the Physiographic Regions of the United States

Bankfull hydraulic geometry relationships are used to estimate channel dimensions for streamflow simulation models, which require channel geometry data as input parameters. Often, one nationwide curve is used across the entire United States (U.S.) (e.g., in Soil and Water Assessment Tool), even though studies have shown that the use of regional curves can improve the reliability of predictions considerably. In this study, regional regression equations predicting bankfull width, depth, and cross-sectional area as a function of drainage area are developed for the Physiographic Divisions and Provinces of the U.S. and compared to a nationwide equation. Results show that the regional curves at division level are more reliable than the nationwide curve. Reliability of the curves depends largely on the number of observations per region and how well the sample represents the population. Regional regression equations at province level yield even better results than the division-level models, but because of small sample sizes, the development of meaningful regression models is not possible in some provinces. Results also show that drainage area is a less reliable predictor of bankfull channel dimensions than bankfull discharge. It is likely that the regional curves can be improved using multiple regression models to incorporate additional explanatory variables. (KEY TERMS: streams; fluvial geomorphology; bankfull discharge; nationwide and regional regression equations; hydrologic modeling.) Bieger, Katrin, Hendrik Rathjens, Peter M. Allen, and Jeffrey G. Arnold, 2015. Development and Evaluation of Bankfull Hydraulic Geometry Relationships for the Physiographic Regions of the United States. Journal of the American Water Resources Association (JAWRA) 1-17. DOI: 10.1111/jawr.12282