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Suburban sprawl and poor preparation worsened flood damage in Louisiana

U.S. Coast Guard personnel rescue stranded residents in Baton Rouge on August 14, 2016. U.S. Department of Agriculture/Wikipedia, CC BY

Suburban sprawl and poor preparation worsened flood damage in Louisiana

U.S. Coast Guard personnel rescue stranded residents in Baton Rouge on August 14, 2016. U.S. Department of Agriculture/Wikipedia, CC BY

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.

Amite River basin. K. Musser/Wikipedia, CC BY-SA

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 US$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.

After the 1983 flood, local officials began taking steps to improve flood protection systems and reduce risk. They included raising and modifying highway bridges that impeded the flow of river water, and upgrading levees and pumps to manage excess backwater flooding in the lower reaches of the river basins.

Baton Rouge, the state capital and largest city in the region, and Denham Springs modified their floodplain building standards to reduce risk. And public officials secured authorization in 1986 for the Corps of Engineers to build a diversion canal to redirect excess water from the upper Comite River basin to the Mississippi. Local voters even approved a tax to fund a portion of the project in 2000. By all appearances, it seemed that communities were responding to Emmer’s appeal.

Growth pressures in flood-prone basins

However, these efforts have not been sustained. Suburban sprawl has spilled onto floodplains and placed residents at risk.

For example, the relatively new incorporated community of Central in East Baton Rouge Parish reports that 75 percent of its territory is in the 100-year floodplain. According to initial news reports, up to 90 percent of the town’s houses sustained damage in this month’s floods.

Between 2000 and 2010, the population of Ascension Parish grew from 76,617 to 107,215, and Livingston Parish’s population increased from 91,814 to 128,026. Developers have intensively built up areas along the Comite and Amite rivers and in the territory where the two rivers converge and back up into Bayou Manchac during floods. Meanwhile, the Comite River Diversion Canal has received irregular and inadequate funding and is years from entering operation.

Planned Comite River Diversion Canal Project (click for larger image). Louisiana Department of Transportation and Development

Many properties that sustained damage this month lie outside of the 100-year floodplain in developments approved by local agencies. There has been no effort to deflect development or require safe construction practices within the 500-year floodplain, even though the region’s flood history suggests that broader flood mitigation efforts would be prudent.

A false sense of security

Since Congress passed the Disaster Relief Act of 1950, the federal government has provided relief and recovery funds after large-scale floods and other disasters. These payments, along with federally funded levees and other flood control structures, have created a false sense of security in the face of risk.

For centuries before the National Flood Insurance Program was created in 1968, Louisiana residents who lived in flood-prone areas took steps to reduce their personal risk. Native Americans built their mounds and communities on terraces above flood-prone rivers. During colonial times, people built houses in floodplains with living quarters five to eight feet above ground level. Spanish soldiers assigned to the much-detested military garrison on Bayou Manchac abandoned it due to its tendency to flood soon after Spain ceded its Florida territory to Britain in 1763. Most of them moved to higher ground in Baton Rouge.

A colonial-era house in Baton Rouge illustrates the traditional practice of building houses raised aboveground. Craig Colten, Author provided

After Louisiana joined the United States, residents continued to build houses along rivers or near the coast on stilts. In the 19th century, coastal dwellers began gradually retreating inland. And many residents in flood zones maintained modest dwellings and furnishings, which minimized replacement costs after high-water events. Tied to local livelihoods and intent on remaining in place, they made deliberate decisions to live with risk and built homes accordingly.

Recently, however, suburban sprawl has spurred enactment of building codes that mandate building techniques using concrete slab foundations set directly into the ground. And increasing affluence has enabled families to purchase larger dwellings in areas of high and moderate flood risk. Under the National Flood Insurance Program, buyers must obtain federal flood insurance to qualify for mortgages in 100-year flood zones, but some properties near flood zones do not face the same requirement.

Flood waters recede slowly around a newer house built on a concrete slab foundation in Ascension Parish. Craig Colten, Author provided

Consequently, many families purchased homes in areas of relatively low risk without flood insurance. Others allowed their insurance to lapse. Surrounded by new developments, many newcomers likely never realized they were anywhere near flood-prone rivers.

Disasters tend to spark short-lived interest in learning lessons from tragedy. Perhaps local officials can parlay the obvious lesson of inadequate follow-through on the Comite diversion canal into new funding. More importantly, the Federal Emergency Management Agency should factor this month’s floods into the flood zone maps, so that this extreme event becomes part of the baseline for delimiting risky areas. And state or local officials might consider expanding the territories eligible for insurance to the 500-year floodplain.

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.