Season of the Scour
Jul 20, 2013
The Chinese term for what's going on here gets translated as sand-washing, but the operation is really more like sand-blasting. Every summer, just before the rainy season, specialized gates in a dam holding back the Yellow River are opened wide, and the river bursts through under such high pressure that the sand and silt in the river water scour the river bottom for the next 800 km.
The nozzles will be left open for about three weeks, till the water level in the Xiaolangdi Reservoir is low enough to accommodate summer rain and the riverbed downstream has been blasted deep and clean. In its lower reaches, the Yellow River meanders slowly and is prone to silt buildup and flooding. In recent years, sand-washing has been undertaken at least once and usually twice a year.
The photo above shows the sand-washing last week; recent rains had stirred up the sediment in the water, turning it all yellow. The photo below shows the beginning of last summer's sand-washing operation, which took place after a dry spell during which the sediment had precipitated out of the water column and settled to the bottom of the reservoir.