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Abstract

Dryland channel networks share many similarities with channel networks in more humid regions, but they are also unique in having: extreme temporal and spatial variability in rainfall, runoff, and both hillslope and channel processes; poor integration between tributary and main channels; dominantly ephemeral or intermittent flow; and lack of equilibrium between process and form. Floods are likely to be particularly important in dryland channels, and riparian vegetation exerts a strong influence on channel processes and form. Land managers working in dryland channel networks particularly need to answer the following questions: What is stable? What is the role of disturbance? How do ecosystems depend on physical form and process?

This paper explores methods for determining thresholds and resiliency within a channel network and suggests metrics that can be used to assess the condition of a channel segment or entire drainage network relative to management goals. The management metrics focus on flow regime, sediment supply, bed grain size, bedform configuration, width/depth ratio, bed gradient, channel planform, and extent and type of riparian vegetation. For each of these metrics, geological, historical, and systematic records can be used to define the natural range of variability for a particular channel form in the absence of direct land-use impacts. The range of variability present under land use such as military training activities can then be compared to the natural range to assess whether these activities are negatively affecting the dryland channel network. The Yuma Wash drainage in the Yuma Proving Ground, Arizona, is used as a case study.

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