Hole in the Clouds

The Many Webs of Pakistan

Apr 6, 2011

Last summer, when floodwaters swamped one-fifth of all the land in Pakistan, spiders were among the creatures struggling to escape the rising waters. Spiders moved up into the trees, while the water on the ground stayed high for so long that the new eight-legged tree-dwellers had plenty of time to spin web upon web among the branches.

Today, many of the trees of Pakistan are tangled up in spiderwebs. And it has been reported that many of the mosquitoes of Pakistan have been snagged in the webs, resulting in a much smaller than anticipated post-flood mosquito problem.

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.