Continental-scale relationship between bankfull width and drainage area for single-thread alluvial channels

Abstract

We explore the bankfull width (Wbf) versus drainage area (A da) relationship across a range of climatic and geologic environments and ask (1) is the relationship between ln(Wbf) and ln(A da) best described by a linear function and (2) can a reliable relationship be developed for predicting Wbf with Ada as the only independent variable. The principal data set for this study was compiled from regional curve studies and other reports that represent 1018 sites (1 m≤Wbf≤110 m and 0.50 km2≤A da≤22,000 km2) in the continental United States. Two additional data sets were used for validation. After dividing the data into small, medium, and large-size basins which, respectfully, correspond to A da<4.95 km2, 4.95 km2≤A da<337 km2, and Ada≥337 km2, regression lines from each data set were compared using one-way analysis of covariance (ANCOVA). A second ANCOVA was performed to determine if mean annual precipitation (P) is an extraneous factor in the Wbf versus A da relationship. The ANCOVA results reveal that using Ada alone does not yield a reliable Wbf versus Ada relationship that is applicable across a wide range of environments and that P is a significant extraneous factor in the relationship. Considering data for very small basins (Ada≤0.49 km2) and very large basins (Ada≥1.0 × 105 km2) we conclude that a two-segment linear model is the most probable form of the ln(Wbf) versus ln(Ada) relationship. This study provides useful information for building complex multivariate models for predicting Wbf. Key Points The bankfull width versus drainage area relationship is scale dependent Bankfull width cannot be reliably predicted using drainage area alone Precipitation is a significant factor for predicting bankfull width © 2014. American Geophysical Union. All Rights Reserved.