Forty years' channel change on the Yongdinghe River, China: patterns and causes

In the last 40 years, the Beijing section of the Yongdinghe River evolved from a perennial and wandering river reach to a channellized and fragmentation dry river channel. Such changes threatened the local safety, eco-environment health, and economy development. In order to clarify the channel change patterns and its mechanisms, the spatial and temporal changes of the river channel and the causes are analysed. The results show that the river channel was greatly reshaped by the intensive land using, with a total of 66.95 km ² degraded area including the overflow land, water area, and agricultural land. The overflow land was mainly changed to dry riverbed, agricultural land, water conservancy construction land, planted woodland, and bare land. The water area was mainly replaced by dry riverbed, channellized watercourse, water conservancy construction land, and agricultural land. Agricultural land was mainly changed to residential land, dry riverbed, and bare land. The abrupt river runoff and sediment change after construction of the Guanting Reservoir (the largest reservoir in the Yongdinghe River) indicates a potential trigger for the river channel changes. The river channel change processes are finally concluded: before 1980, the large number of the water conservancy projects' construction including the reservoirs, check dams, and sluice in the Guanting Gorge (upstream of the study river reach) changed the river connectivity and the flow continuity of the upstream river channel. Together with the water use, the soil and water conservation activities, and the variable precipitation, almost all the runoff and sediment to the study river reach were intercepted; then the perennial dry up river and the increased land requirement impelled people to occupy the downstream river space.