Relentless storms that soaked the Ohio and Mississippi River river basins last month spared Louisiana, but our state is still going to feel the aftermath when record rainfall makes its way down the swollen Mississippi.
Gov. Bobby Jindal described the situation as "a massive amount of water heading our way."
Indeed, forecasters are predicting a crest that rivals the historic 1927 flood, the disaster that prompted a change in how this country deals with river flooding. The solution -- spillways that divert water from rivers and take pressure off levees -- is proving its value again this year.
The Bonnet Carre Spillway in St. Charles Parish, which diverts river water into Lake Pontchartrain, and the Morganza Spillway, which diverts water into the Atchafalaya Delta, were built to prevent a bloated Mississippi from flooding populated areas.
Louisiana officials will open the Bonnet Carre Spillway Monday, the ninth time it has been used to relieve pressure on Mississippi River levees. A decision on whether to open the Morganza Spillway -- for the first time since 1973 -- will be made soon thereafter.
That seems likely to happen, given the most recent river forecast provided to Louisiana officials. It showed that even if all 350 bays of the Bonnet Carre were to be opened, the Mississippi River would still rise to 19.5 feet, a half-foot from overtopping the floodwalls in downtown New Orleans.
But together, the two spillways are expected to keep the river level in New Orleans at 17 feet when the river crests on May 24, well below the 21-foot record that was reached in 1927. The floodwalls are designed to protect downtown New Orleans to 20 feet.
The safety margin provided by diverting the river and the other steps that are being taken to prepare for a rising river are reassuring. Gov. Jindal has already activated the Louisiana National Guard to assist with flood prevention efforts. The state will make evacuation plans and decisions about where to place sandbags as soon as it has computer modeling from the Corps of Engineers showing the effect that opening the Morganza Spillway will have on Terrebonne and St. Mary parishes.
The corps has also started daily inspections of levees along the Mississippi and Atchafalaya rivers, an activity that is triggered as soon as the river reaches 15 feet. Inspectors look for areas of seepage and sand boils.
Focusing on the river threat is absolutely the right priority now, although there are implications for hurricane protection. The corps has suspended work on a 15-mile stretch of the Mississippi River levee from English Turn to Oakville because of a rule that prohibits subsurface and surface work within 1,500 feet of river levees once the river reaches 15 feet.
Since the river isn't expected to fall under 15 feet until mid-June, the corps won't be able to finish that levee work by its self-imposed June 1 deadline for providing hurricane protection from a 100-year storm.
Missing the deadline is unfortunate, and the situation does expose parts of metro New Orleans to potential risk. If an early season tropical storm or weak hurricane were to hit in the right spot, the river levees could be overtopped, said Joannes Westerink, a professor of civil engineering and hurricane surge modeler who is a member of the Southeast Louisiana Flood Protection Authority-West.
But the threat posed by the engorged Mississippi River is not remote -- it's already obvious as the huge volume of water moves down the river. The steps being taken are necessary and appropriate.
"Public safety is our top priority,'' said Col. Ed Fleming, commander of the New Orleans District of the Army Corps of Engineers, "and the public safety in front of our face is a riverine flood.''
That's true, and that same threat is what prompted the corps to blow up a river levee in Missouri to activate the New Madrid Floodway, a decision that flooded farmland but protected more populated areas.
Opening the floodways here will have some negative effects, too. In Morgan City, for example, some businesses are located on the water side of floodwalls, and the state is getting ready to fight flooding there and in other communities in St. Mary and Terrebonne parishes.
River water diverted through the Bonnet Carre spillway will mean a fresher Lake Pontchartrain, and the change in salinity will chase some species away, a situation that's most likely to affect brown shrimp at this time of year. The nutrient rich river water is also likely to create big algae blooms in the lake.
But thankfully, the effects on the lake are temporary. Past spillway openings have done little long-lasting damage. There are even some indications that previous spillway openings helped the lake by depositing sediment on the bottom, repairing damage done by shell dredging before it was banned. The corps also has a detailed environmental monitoring plan for the lake and will track water quality, dissolved oxygen and sediment.
Any ill effects pale compared to the possibility of devastating flooding, like the 1927 disaster that inundated more than 23,000 square miles, leaving hundreds of thousands displaced.
South Louisiana residents can count themselves lucky that there are effective safety valves in place for this very set of circumstances, and that we learned important lessons from past disasters.
"We haven't seen flooding like this in quite awhile,'' Gov. Jindal said. "The water will be higher and the duration will be longer.'' But he also noted that the corps does not anticipate overtopping of mainline levees along the Mississippi River.
That's a relief.