Arroyos are dramatic features of the landscape, but their formation depends on the supply of sediment that comes into the valley from the less dramatic hill slopes, which cover more than 90% of the landscape. Scientists have installed simple instruments that catch water and sediment on hill slopes during precipitation events. After each event, scientists weigh the sediment and water produced by each small test area. They also monitor precipitation, streamflow, and sediment transport in nearby streams in order to better understand the magnitude of each event. These studies provide quantitative data on the supply of sediment from uplands into stream channels, and relationships between precipitation rates and rates of sediment movement.

Preliminary results indicate that the amount of sediment moved by rainstorms of similar magnitude varies over a wide range. Random processes or unmeasured variables (raindrop size, for example) cause these variations. Measurements of numerous events will be required in order to develop reliable quantitative models of sediment movement.

Upland studies have been designed to compare sediment production between areas that have been managed with differing levels of grazing. One study site has won awards for its protective range management practices, while another has numerous erosion features that are the result, in part, of sparse vegetation.

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U.S. Department of the Interior
U.S. Geological Survey
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Maintained by Richard Pelltier
Last modified: 15:04:23 on 15-Mar-2006