Wednesday in Baton Rouge, the Coastal Protection and Restoration Authority met. One topic was the potential for Spring floods. As with every Spring, eyes are watching water levels on the Mississippi River. Snow melt and Spring rains annually raise the level of the river, but more in some years than others. In 1927, record rains in the upper watershed resulted in one of the greatest floods in American history. Heavy rains and snowfalls throughout the winter of 2009-10 have kept the Mississippi River at near record levels, thus making many wonder how Spring will add to the flood threat.
Jeff Graschel of the National Oceanic and Atmospheric Administration (NOAA) talked a about current river levels as well as the forecast. Graschel reports that due to warm weather in the Midwest, most of the winter snow pack has melted. Driven by a mild El Nino event, the Gulf of Mexico states have been wetter than usual, but states along the Ohio River Valley have been drier than usual. The Ohio River contributes nearly 2/3 of the total flow of Mississippi River. Currently, a large flood wave is moving down the Ohio towards the Mississippi, though this is expected to only result in minor flooding, meaning mostly agricultural lands, with little threat to homes and businesses. Many of the smaller tributaries are forecast to crest above flood stage, including the Amite and Comite Rivers near Baton Rouge. The Pearl River, in eastern Louisiana, has been at or above flood stage most of the time since September of 2009 and will continue to stay high.
How high will the Mississippi river get? The biggest unknown is future rainfall. Though El Nino is making things drier in the upper basin, this pattern could change. Graschel said if mother nature is not kind and heavy rains fall, minor flooding could get worse. Several times throughout the winter, state and federal agencies have been put on alert to monitor the river levels and stresses to the levee protection system. As river levels rise well above flood stage, plans are activated to open existing river diversions and spillways such as the Bonnet Carre, just up river from New Orleans. The Bonnet Carre has only been opened 8 times since the flood of 1927 and is designed to carry up to 250,000 cubic feet per second, or roughly 20% of the Mississippi River at peak flow.