A barrier for holding back water, usually in the form of a reservoir, which may be used to generate electricity and/or to supply irrigation water. Csiki and Rhodes (2010) PPG 34, 6 review current knowledge related to the influence of run-of-river dams on the hydraulics and geomorphology of rivers and suggest types of studies that need to be undertaken to address gaps in current knowledge. See Graf (1999) Water Res. Research 35, 4, 1305 on the large-scale hydrologic impacts of the 75000 dams in the United States.