Arroyo channel head evolution in a flash-flood-dominated discontinuous ephemeral stream system

Geological Society of America Bulletin
By: , and 



We study whether arroyo channel head retreat in dryland discontinuous ephemeral streams is driven by surface runoff, seepage erosion, mass wasting, or some combination of these hydrogeomorphic processes. We monitored precipitation, overland flow, soil moisture, and headcut migration over several seasonal cycles at two adjacent rangeland channel heads in southern Arizona. Erosion occurred by headward retreat of vertical to overhanging faces, driven dominantly by surface runoff. No evidence exists for erosion caused by shallow-groundwater–related processes, even though similar theater-headed morphologies are sometimes attributed to seepage erosion by emerging groundwater. At our field site, vertical variation in soil shear strength influenced the persistence of the characteristic theater-head form. The dominant processes of erosion included removal of grains and soil aggregates during even very shallow (1–3 cm) overland flow events by runoff on vertical to overhanging channel headwalls, plunge-pool erosion during higher-discharge runoff events, immediate postrunoff wet mass wasting, and minor intra-event dry mass wasting on soil tension fractures developing subparallel to the headwall. Multiple stepwise linear regression indicates that the migration rate is most strongly correlated with flow duration and total precipitation and is poorly correlated with peak flow depth or time-integrated flow depth. The studied channel heads migrated upslope with a self-similar morphologic form under a wide range of hydrological conditions, and the most powerful flash floods were not always responsible for the largest changes in landscape form in this environment. 

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Arroyo channel head evolution in a flash-flood-dominated discontinuous ephemeral stream system
Series title Geological Society of America Bulletin
DOI 10.1130/B31064.1
Volume 126
Issue 11-12
Year Published 2014
Language English
Publisher Geological Society of America
Contributing office(s) Earthquake Science Center
Description 19 p.
First page 1683
Last page 1701
Country United States
State Arizona
Online Only (Y/N) N
Additional Online Files (Y/N) N
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