Undoing Damage to a Disappearing Delta

University of Texas geologists are floating a plan they believe will reverse the Louisiana delta and coastal marsh land loss that has proceeded at a clip of tens of acres per day, every day, since the 1940s.

Earth science news from a month ago featured a pretty grim prognosis for the disappearing major river deltas around the world. While sea level change plays a role, the largest threat to deltas comes from engineering initiatives that we’ve imposed on river systems. Not that anything was done without the best of intentions — after all, we’re talking about dams and levees for flood control and power generation — but our hard structures have yielded some hard truths.

By drastically altering the amount of sediment that a naturally flowing river would deliver to the delta at its mouth, dams, levees and the like basically starve the delta of its source of sustenance. These soft soils become compacted under their own weight over time, so with out fresh sedimentary reinforcements coming in to rebuild and replenish, the delta becomes susceptible to land loss.

It all reminds me of a childhood riddle:

Q: Why did the idiot beat his head against the wall?

A: Because it felt so good when he stopped.

It seems that the obvious thing to do, when what you're doing does harm, is to just stop. But referring to the point made above, we’ve come to depend on our dams and levees, so just doing away with them isn’t so simple. And here’s where the engineering comes in handy.

What Texas geologists David Mohrig and Wonsuck Kim have proposed, reported by ScienceDaily and as published by the American Geophysical Union, are carefully controlled breaches of the levee system on the Mississippi River a bit downstream of New Orleans.

These breaches would permit sediment-rich river water to once again spill onto marshland starved for sediment, but would maintain a water level in the river that would still permit commercial traffic to navigate the important waterway.

According to the calculations performed by Mohrig and Kim, the plan would reduce by about half the rate of future land loss that will occur in the absence of any remedial measure.

It may not be a complete and perfect solution to Mississippi delta land loss, but it’s a great start. After all, it’s the sediment that counts.

Photo courtesy of U.S. Fish and Wildlife Service, via Wikimedia Commons