Abstract

Although many arid badland channels erode rapidly, channel flows appear to be rare, raising the issue of the character and frequency of flows responsible for channel erosion. Using an acoustic stream gauge, we recorded nine flash flood hydrographs over a 3 yr period from the Upper Blue Hills badlands, Utah, with maximum discharges up to ∼ 9 m3/s. Flow hydrographs reveal bores and rapid depth changes that are similar to flash floods observed elsewhere. Bore and hydrograph peak translation velocities are greatest in narrow channel segments. Rapid runoff generation during short-duration thunderstorms produced complex hydrographs whose shapes appear to reflect channel network geometry. Storm runoff response is highly sensitive to antecedent moisture, which greatly reduces the regolith infiltration capacity. High antecedent moisture coupled with a relatively low intensity, long-duration rainstorm produced the largest flow event. Estimating flow frequency in this landscape therefore requires knowledge of the distributions of both storm sizes and temporal spacing relative to the short time required for the regolith infiltration capacity to recover following wetting, here roughly 24 hr. Landscape changes can be produced not only by rare, large rainfall events, but by a broad range of storm size and frequency under optimal antecedent moisture conditions.

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