Saturday, May 14, 2011

When Levees Aren’t Enough

Today thousands of people are out keeping an eye on the levees. In Manitoba, the province finally cut a hole in one dike to lower the water in a flooded river, the Assiniboine, which is still days away from cresting. In Mississippi, a century-old levee fell apart after water started to flow over the top, something that had never happened before. Water is overtopping dozens of backwater levees on tributaries of the Mississippi River, but most of them are still holding. Here too it is at least two days before the crest in the river. In Louisiana, for the first time, the Army Corps of Engineers has opened all three of the major spillways for the Mississippi delta, diverting a flow of water considerably larger than the average total flow of the river. The three diversions may lower the river enough to save New Orleans, but it all depends on the levees there. A river flood in New Orleans would be far more serious than the hurricane flooding the city has experienced. The hurricane flood water sat near sea level, but a river flood could potentially fill the city with flowing water that remained 10 meters above sea level for a month.

If people are already pointing fingers over the flood control systems that didn’t completely prevent the flooding, it is little more than a sign of the frustration and uncertainty that goes with trying to control a force of nature. Nature, after all, is hard enough to predict, harder still to control. More rain fell today over most of the Mississippi basin. It wasn’t much rain, but any runoff at all delays the day when the rivers return to their normal levels.