LSU study looks at better grass for New Orleans levee system
Reconstruction on the levees of New Orleans has been in the news a lot since Hurricane Katrina demolished them in 2005, but one aspect of the effort to rebuild and solidify them that hasn’t been addressed is their vegetative covering. Because of the danger of erosion and cracking, it is essential that grass be established on those berms and thrive, or the levees have a higher chance of eroding or breaking.
“This may be the most important work we ever do,” says Ron Strahan, assistant professor of turfgrass and ornamental weed science at Louisiana State University (LSU). In fact, it could be a life or death issue. He and Jeff Beasley, also an assistant professor of turfgrass science at LSU, are conducting research on the New Orleans levees that is aimed at establishing and maintaining healthy grass on the tops and sides of the protective structures.
It is not an easy task. Picture this: a man-made berm that has been constructed of clay soils and compacted so densely that it can withstand the battering of a hurricane. It has an almost impervious surface, a high salt content and steeply sloped sides. It is designed so that water runs off without penetrating and weakening the levee. How do you establish and nourish grass so that the roots will help hold that earthen levee together?
Strahan and Beasley are conducting five separate, but somewhat overlapping studies that are looking at factors such as seeding rates, grass varieties, mulches and planting schedule. It’s all part of the overall effort to keep those levees intact during the next big hurricane. “That’s the reason the city flooded, is the levees failed,” Strahan says. The U.S. Corps of Engineers, which has the overall responsibility, is the primary funding agent for the university’s studies.
|Photos Courtesy of Ron Strahan.|
|One LSU study is looking at grass species such as common bermudagrass, annual ryegrass and seashore paspalum in replicated trials.|
|In order to develop better grass growing protocols for the New Orleans levee system, LSU is conducting trials that ultimately could help save lives.|
Private landscape companies are hired to establish turf on the New Orleans levees, and over time a hay-like ground cover can be established. The usual method of establishment is to hydroseed a new levee in the spring with a mix of common bermudagrass and annual ryegrass seed, along with a healthy slurry or mulch, without irrigation. However, because of the harsh soil conditions and vagaries of weather and rainfall, it can take years to get a permanent stand, and the growth and stand can be patchy. Those open areas can be hazardous to the levee. The steep slopes also pose a problem, since a heavy rain on the fresh hydroseeding can wash away the entire planting.
LSU has been trying to assist the companies, but the new studies are designed to set up entirely new protocols for turf establishment so that the levees can be quickly protected and made less worrisome during stormy weather. These replicated trials hopefully will give the landscape companies a better methodology and better results, with the ultimate beneficiaries being the residents of New Orleans. The information could also be used in the planting of turf in harsh coastal conditions in other areas of the world.
“They have to have something protecting the levees at all times,” Beasley says, and these trials may provide a more solid foundation for turf establishment. There are 1,300 miles of levees in question in the New Orleans area, so this will have a large overall effect.
The first trial began in January of this year, and it has already yielded significant results, Strahan says. This was a bermudagrass/ryegrass seeding and germination trial, testing the normal method of seeding. They found that using un-hulled bermuda seed may not be the best way to go, and that the ryegrass may inhibit germination and establishment of the bermudagrass, which is targeted to be the ultimate permanent ground cover because of its resiliency at maturity. It is also the species that will grow best during the hot months of hurricane season.
A better method may be to plant ryegrass on a new levee in the winter, and then kill it back in the spring with herbicides as the bermudagrass is seeded, the turf scientists say. Spring is not prime hurricane season, so it is actually a good time to establish grass. Rather than overseed bermudagrass in the winter with ryegrass, it should be enough to have dormant bermuda there because the plants and roots are still thriving. It is warm enough in this subtropical climate to remain healthy, even if it does go brown after cold nights.
The other studies are ongoing, and no results are available yet. Beasley and Strahan are looking at seeding rates of bermudagrass, the incorporation of seashore paspalum as a salt-tolerant alternative, the use of mulches and other soil amendments, like gypsum, to combat the harsh soils, and the validity of using temporary irrigation to help get bermudagrass seedlings going. This area gets 60 or more inches of rain annually, but in the spring there can be long dry periods between rainstorms.
Since fertility can be an issue, they are also incorporating some organic matter and other fertilizers into their slurry mixes to see if that can speed up establishment. There is no ability to leach salts out of the levees, most of which are massive structures, so they are also testing gypsum and other amendments that can sweeten the soil. Straw and tackifiers are also being employed in some areas, and they want to try some rototilling of the surface to break open the hardpan clay. They lease a water truck to use for irrigation, and they purchased a small, trailer-mounted hydroseeder to use for planting trials.
Strahan and Beasley feel that common bermudagrass is an excellent choice for the levees; hybrids could be too high-maintenance. Speed of establishment is an important consideration, because once a levee is built it should be protected immediately. A part of their trials is to evaluate the different treatments on erosion control. The fact that the levees are built with exactly the opposite attributes of a good turf planting medium is the source of all the problems with establishment, but the turf growers can’t change what they are given.
“When we give them an answer, we want it to be an answer based on results,” Beasley says, because so much of what has gone before and is not working comes about because of trial-and-error methodologies.
“We do feel it’s a personal issue, of course,” says Strahan, a native Louisiana boy. And, although the LSU campus in Baton Rouge was out of the zone of devastation, he still feels this is important work. Beasley is new to the state, but he also feels it’s important that they are doing something that could lessen future hurricane damage.
Don Dale is a freelance writer and a frequent contributor. He resides in Altadena, Calif.