Effect of check dams on runoff, sediment yield, and retention on small semiarid watersheds

Erosion dynamics in semiarid environments is defined by high magnitude, low frequency rainfalls that produce runoff with high sediment concentration. Check dams are widely used in this environment as a sedimentation mitigation technique, however their impact on overall watershed sediment balance is not well known. In 2008 a total of 37 loose rock semipermeable check dams were installed on two small (4 and 3.1 ha [9.8 and 7.6 ac]) watersheds located on the alluvial fan of the Santa Rita Mountains in southern Arizona. Each watershed was equipped with a rain gauge, supercritical flow flume, and sediment sampler. The runoff and sediment yield characteristics following the check dam installation were compared with 35 years of historical records. Impacts of the check dams on runoff from major rainstorms were not detectable; however the number of runoff events generated by small (less than one year recurrence interval) rainstorms decreased by 60%. During four years check dams retained 75 t (82.6 tn) of sediment (50% of sediment yield) and were filled to more than 80% of their capacity. Depositional areas upstream of the dams have potential to support watershed restoration.