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

We explore the bankfull width (W-bf) versus drainage area (A(da)) relationship across a range of climatic and geologic environments and ask (1) is the relationship between ln(W-bf) and ln(A(da)) best described by a linear function and (2) can a reliable relationship be developed for predicting W-bf with A(da) 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 mW(bf)110 m and 0.50 km(2)A(da)22,000 km(2)) 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 km(2), 4.95 km(2)A(da)<337 km(2), and A(da)337 km(2), 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 W-bf versus A(da) relationship. The ANCOVA results reveal that using A(da) alone does not yield a reliable W-bf versus A(da) 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 (A(da)0.49 km(2)) and very large basins (A(da)1.0 x 10(5) km(2)) we conclude that a two-segment linear model is the most probable form of the ln(W-bf) versus ln(A(da)) relationship. This study provides useful information for building complex multivariate models for predicting W-bf. 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