Studying Katrina helps Song find safer, economical ways to strengthen flood protection systems




Studying Katrina helps Song find safer, economical ways to strengthen flood protection systems

Calendar Icon Sep 16, 2015      Person Bust Icon By Karl Vogel     RSS Feed RSS

Chung Song, associate professor of civil engineering
Chung Song, associate professor of civil engineering
The unusually high amount of rain that has fallen locally this summer has focused more attention on the floodwater control systems in Eastern Nebraska.

While those levees and other systems have performed as designed, Chung Song is interested in finding ways to make protecting communities both safer and more economical.

In his first semester at UNL, the associate professor of civil engineering is bringing a wealth of experience he gained over the past decade from studying the impact of hurricanes Katrina and Isaac on New Orleans that he hopes can be applied to flood protection systems across the United States.

“Even though the whole of New Orleans was flooded, that doesn’t mean the whole flood wall failed, it was just a couple of sections of the wall that failed. Most of the walls remained intact,” Song said. “Only one or two failures in the flood wall sections can flood the whole city.

“The difference between this and other work of this kind is that we didn’t intend to figure out who was wrong and what went wrong,” Song said. “We learned a lot of lessons and we tried to use the lessons to find a retrofitting technique that would not only be robust but economical.”

In late August 2005, Katrina caused nearly $81 billion in property loss and close to 1,800 casualties when it walloped New Orleans with a direct hit. The flood waters that inundated the levee system rose so quickly that pumping stations were overwhelmed and shut down. That resulted in two types of damage to the levee walls:

* Water quickly rising and flowing quickly over the cement flood walls, then shooting down the back sides with enough force to wash away the soil holding the walls in place.

* Water pressure pushing against the tops of the walls with great force and pushing out the bottoms of the walls that were anchored in the soil. This created gaps that were filled with water and weakened the foundations as some clay soils of Louisiana become saturated, loses nearly all of its friction and “becomes as slick as grease,” Song said.

With a grant from the Department of Homeland Security, Song and a team of researchers from the University of Mississippi designed a bridging cap – 2-foot-by-1.2 foot, U-shaped, composite joint – that could be placed atop the points where two sections of the foot-thick walls meet, giving support to both sections.

The cost of creating and installing each of these caps, which would be installed about every 25 feet, would be about $40 each. Song said this could save billions of dollars over the cost of renovating the flood water system.

Song’s team also found success with other possible solutions – installing a foot-wide strip of a soil mixture may self-seal the gap between the flood wall and the level soil and growing vetiver, an Asian bunchgrass, to create a system of thick, rope-like roots that would reduce levee erosion.

Song is hopeful the federal government will consider implementing his team’s findings for long-term levee and flood wall system designs and thinks this type of work can continue at UNL.

“I think this work is quite unique. We tried to find out resilient, but economic solutions,” Song said. “There are levee systems everywhere in the nation, and they’re similar to those in New Orleans. It wouldn’t be that hard to see them protecting people here in Nebraska, hopefully.”

Read more about the new engineering faculty