Climate-invariant area-slope relations in channel heads initiated by surface runoff

We use a dataset of 38 field-mapped channel heads from a semi-arid environment in western Colorado to examine relationships between contributing drainage area (A) and local hillslope gradient () in relation to dominant process of initiation (surface runoff versus subsurface flow). Channel heads resulting primarily from subsurface flow have significantly greater values of A, longer basin lengths, and shallower local gradients than channel heads resulting primarily from surface runoff. We also compare the data from western Colorado to six analogous datasets from more humid regions in other portions of the United States and in southeast Australia. Comparison of the confidence intervals for the exponent values of A- regression lines reveals that the confidence intervals for the exponent of western Colorado channel heads with both surface and subsurface flow overlap with the confidence intervals for the exponent of all other datasets. This suggests that A- relationships do not differ significantly between diverse geographic locations. Copyright (c) 2017 John Wiley & Sons, Ltd.