Shaanxi, Ansai: the reservoir of a check dam is filled mostly with eroded silt - only the portion next to the dam is covered with water. (What we are seeing is the reservoir on the upstream side of a check dam built across a gully. The downstream side is not clearly visible. The function of the dam is to reduce the rapidity of the flood flow, and to trap eroded silt from reaching the rivers, creating at same time arable land for a hilly region, and retaining water for irrigation. Such dams achieve several objectives, and are crucial to the development of the loess plateau.)
Picture source: Land Resources in the Loess Plateau of China, edited by The Northwest Institute of Soil and Water Conservation, Academia Sinica, published by Shaanxi Science and Technique Press, 1986.