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The impacts of porous rock check dams on a semiarid alluvial fan

M.H. Nichols, V.O. Polyakov
Science of the total environment 2019 v.664 pp. 576-582
backfilling, incising, land degradation, monitoring, pollution load, runoff, sediment yield, sediments, vegetation, watersheds, Arizona
Low-tech rock check dams are widely used to address land degradation; however, assessments of their impacts on runoff and sediment are lacking and are often limited to the first few years after construction. In 2008, two small (4.0 and 3.1 ha) instrumented watersheds located 300 m apart on an alluvial fan on the Santa Rita Experimental Range in southern Arizona were treated with 37 porous, loose rock check dams. Ten years after construction, the watersheds are experiencing contrasting responses to treatment. The ratio of runoff to precipitation was higher after check dam construction on one watershed and lower on the other, but not significantly in either case. Statistically significant changes in peak runoff rate are not detectable 10 years after construction at either watershed. However, a statistically significant reduction in sediment concentration was found on one watershed and no change was found at the other. The check dams have altered channel grades. However, backfilling of the dams is nearly complete on one watershed and the other has remaining capacity. The alluvial fan setting poses a complex restoration environment due to high sediment loads that deposit in response to vegetated areas of accumulated sediment creating conditions for channel avulsion and new incising concentrated flow paths. Check dams have a lesser impact on watershed outlet runoff and sediment than on internal watershed channel morphology and vegetation establishment. With monitoring and maintenance, check dams can be an effective tool for grade stabilization, but watershed restoration requires additional practices to address degraded interfluve areas.