Floods were sent down the Grand Canyon in 1996 and 2004 and the results were mixed. In 1996 the flood was allowed to go on too long. To start with, all seemed well. The floodwaters built up sandbanks and infused the river with sediment. Eventually, however, the continued flow washed most of the sediment out of the canyon. This problem was avoided in 2004, but unfortunately, on that occasion, the volume of sand available behind the dam was too low to rebuild the sandbanks.This time there is enough sand behind the dam. And most environmental groups argue that these kinds of floods need to happen more often to ensure that sediment levels remain steady. But there's an economic downside to the floods: the water used in the flooding will not go through the hydropower turbines in the upper river, costing those power producers about $1 million. In a month, scientists will be using sonar and surveying tools in the river banks to figure out how well the flood worked. With better models of sandbar formation, they'll be better equipped to decide whether more frequent flooding is worth the high price tag.
Since its construction in 1964, the Glen Canyon Dam in Northern Arizona has depleted the sandy sidebars of the massive Colorado to just one quarter of their original size, leaving archaeological sites vulnerable to wind and destroying the natural habitat of dozens of fish species. To try to remedy this, last Tuesday, authorities flooded part of the Colorado. The man-made flood—using 300,000 gallons of water per second for about 60 hours—was the third in the Grand Canyon in the past 12 years. The previous two weren't entirely successful, asThe Economist points out:(Flickr, via jackfrench)