FloodsSuburban sprawl and poor preparation worsened flood damage in Louisiana
The proximate cause of this month’s extraordinary flooding in southeast Louisiana was a slow-moving storm system that dropped up to two feet of rain in the upper reaches of the Amite and Comite river basins, which drain southern Mississippi and flow into Lake Pontchartrain. There are parallels between the damage of current flooding and the damage caused by Katrina. In both cases, human decisions magnified the consequences of extreme natural events. Planning and permitting enabled development in areas that had experienced repeat floods, and agencies had failed to complete projects designed to mitigate flood damage before the storms hit. If there is one lesson we have learned about floods, it is that records are made to be broken. So in addition to planning for the last flood, we need to anticipate higher water than our current benchmarks.
This month’s extraordinary flooding in southeast Louisiana damaged some 40,000 homes, prompting more than 70,000 people to sign up for FEMA assistance. The proximate cause was a slow-moving storm system that dropped up to two feet of rain in the upper reaches of the Amite and Comite river basins, which drain southern Mississippi and flow into Lake Pontchartrain.
Some affected parishes saw thousand-year rainfalls — precipitation so heavy that forecasters give it only a 0.1 percent probability of occurring any given year. This was unquestionably a rare event.
Reports of flooding in Louisiana may conjure up images of Hurricane Katrina, but these rivers are completely separated from the Mississippi River, and these floods posed no threat to New Orleans. Nonetheless, based on my experience studying risk and resilience in this region, I see parallels between the damage of current flooding and the damage caused by Katrina. In both cases, human decisions magnified the consequences of extreme natural events. Planning and permitting enabled development in areas that had experienced repeat floods, and agencies had failed to complete projects designed to mitigate flood damage before the storms hit.
A region beset by floods
This part of Louisiana, which is known as the Florida Parishes because it once was part of the Spanish territory of Florida, is a natural laboratory for flood studies. A benchmark flood in 1983 caused some $344 million in damages. Additional dramatic floods occurred in 1990 and 1993. In 2001 Tropical Storm Allison dumped 19 inches of rain on Baton Rouge over the course of two days and unleashed extensive inundations. And just last March, 9-15 inches of rain inundated much of the same area.
In 1985 Rod Emmer, the long-time director of the Louisiana floodplain managers’ association, gave a stunningly prescient presentation to a national gathering of floodplain managers in New Orleans. Emmer observed that the devastating 1983 flood along the Amite River was the fourth in an 11-year span, and that losses could have been reduced with sensible flood-reduction projects. He also pointed out that planners had repeatedly called for such action, and concluded that the problem was not a failure to plan, but a failure to follow through and complete projects.
