Submitted to: Water Resources Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/27/2007
Publication Date: 6/28/2008
Citation: Nearing, M.A., Nichols, M.H., Stone, J.J., Renard, K.G., Simanton, J.R. 2008. Sediment yields from unit-source semi-arid watersheds at Walnut Gulch. Water Resources Research. Vol. 43, W06426, doi:10.1029/2006WR005692. Interpretive Summary: Information on sediment export rates from small, upland watersheds in semi-arid regions is limited. The nature of rainfall in semi-arid climates is such that rainfall is infrequent, highly variable both in space and time, and typically very intense. Due to this high variability and infrequency, long measurement records are generally necessary in order to be able to characterize sediment export rates from watersheds. The Walnut Gulch Experimental Watershed has operated since the mid-1950s. This study reports results of eleven recent years of data collection of sediment from small watersheds in Walnut Gulch. The results show that the erosion rates in this area are much greater than rates typically reported for rangelands of Arizona, and that a large fraction of the sediment that is generated comes from a few isolated storms. The erosion rates that we measured appeared to be related both to the vegetation and the general geology of the area. These data will help land managers, government agencies, and conservation groups understand the rates of erosion that can occur on rangelands, and some of the factors that control these rates.
Technical Abstract: This study reports sediment yields from seven small (0.18 to 5.42 ha) watersheds in southern Arizona measured from 1995 to 2005. Sediment concentrations and total event sediment yields were related to storm-runoff characteristics, and statistical relationships were developed to estimate sediment yields for events with missing data. Precipitation ranged from 263 to 298 mm yr-1, runoff 8.2 to 26.4 mm yr-1, and sediment yields 0.07 to 5.7 t ha-1 yr-1, with an areally-weighted average of 2.2 t ha-1 yr-1. For six of the seven watersheds between 6 and 10 events produced 50% of the total sediment yields over the eleven year period. On the seventh watershed two storms produced 66% of the sediment because of differences in the geomorphology and vegetation characteristics of that area. Differences between sediment yields from all watersheds were attributable to instrumentation, watershed morphology, degree of channel incision, and vegetation.