Semiarid watershed response to low-tech porous rock check dams

Authors: Nichols, Mary; Polyakov, Viktor; Nearing, Mark; HERNANDEZ, M. - University Of Arizona

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2016
Publication Date: 7/1/2016
Citation: Nichols, M.H., Polyakov, V.O., Nearing, M.A., Hernandez, M. 2016. Semiarid watershed response to low-tech porous rock check dams. Soil Science. 181(7):275-282. doi: 10.1097/SS.0000000000000160.

Interpretive Summary: Rock check dams are used throughout the world to address erosion problems on degraded lands. Increasingly, they are being used in restoration efforts on rangelands in the southwestern US; however, their impact on watershed response and channel characteristics such as slope and cross section shape is not well quantified. In 2008, 37 porous rock structures were built on two small (4.0 and 3.1 ha) instrumented watersheds on an alluvial fan at the base of the Santa Rita Mountains in southern Arizona, USA. 35 years of historical rainfall and runoff, and sediment data are available to compare with seven years of data collected after check dam construction. In addition, post construction measurements of channel geometry and channel profiles were compared with pre-construction measurements to compute the amount of sediment retained and to assess changes in channel. After seven runoff seasons, 80% of the check dams on one of the watersheds filled to 100% of their capacity. Initially, the check dams altered the ratio of precipitation to runoff, but this did not persistent through the seven years. The contrasting watershed experiences lower sediment yields and only 20% of the check dams on this watershed are filled to capacity. Vegetation has become established at the check dam sites. The check dams continued to influence runoff during small events through the seven years of measurement. Within the watersheds the mean gradient of the channel reach immediately upstream of the structures has been reduced by 35% (from 0.061 to 0.039) and 34% on (from 0.071 to 0.047).

Technical Abstract: Rock check dams are used throughout the world as a technique for mitigating erosion problems on degraded lands. Increasingly, they are being used in restoration efforts on rangelands in the southwestern US; however, their impact on watershed response and channel morphology is not well quantified. In 2008, 37 porous rock structures were built on two small (4.0 and 3.1 ha) instrumented watersheds on an alluvial fan at the base of the Santa Rita Mountains in southern Arizona, USA. Thirty-five years of historical rainfall and runoff, and sediment data are available to compare with seven years of data collected after check dam construction. In addition, post-construction measurements of channel geometry and longitudinal channel profiles were compared with pre-construction measurements to characterize the impact of check dams on sediment retention and channel morphology. The primary impact of the check dams was retention of channel sediment and reduction in channel gradient; however response varied between the proximal watersheds with 80% of the check dams on one of the watersheds filled to 100% of their capacity after seven runoff seasons. In addition, initial impact on precipitation runoff ratios was not persistent after check dams filled to capacity. The contrasting watershed experiences lower sediment yields and only 20% of the check dams on this watershed were filled to capacity and continue to influence runoff during small events. Within the watersheds, the mean gradient of the channel reach immediately upstream of the structures has been reduced by 35% (from 0.061 to 0.039) and 34% on (from 0.071 to 0.047).