Parish levees to be studied for storm surge protection
MORGAN CITY, La. — The St. Mary Parish Levee District approved engineering work on parish levees to compare with U.S. Army Corps of Engineers data to determine the height needed to provide storm surge protection.
The levee district held a special meeting Tuesday at the Port of Morgan City office. The commission approved about $15,000 worth of engineering work, including wave modeling on the Wax Lake Outlet East and West levees, to be performed by engineering firm, T. Baker Smith.
The modeling is to take the worst case scenario of how high a wave could get to on a spot on the levee during a 1 percent storm, said engineer Jason Kennedy of T. Baker Smith.
Engineers will do modeling at two points on the Wax Lake Outlet East and West levees. “Based on past experience in the FEMA, DFIRM (Digital Flood Insurance Rate Maps) appeal process is that the vegetation plays a significant role in attenuating the wave run up in front of these levees,” Kennedy said.
The Wax Lake East, Wax Lake West levees and West Atchafalaya Basin levees are “fronted by densely vegetated forest,” Kennedy said. When the corps did its analysis of the levees, it did not account for vegetation that helps to block some of the storm surge, he said.
There is at least a 100-foot strip of trees “between the toe of the levee and the Intracoastal Waterway,” Kennedy said.
The corps stated in a report that portions of these levees need to be raised six or seven feet in some places, he said.
“The corps told us that their analysis for that 1 percent design elevation was not based on real data. They used a lot of theoretical data and a lot of assumptions there,” Kennedy said.
“We’ll analyze this thing and take the worst-case fetch length, which couldn’t be more than 1,000 feet of open water that unaltered wind could generate and blow a wave,” Kennedy said.
Bill Hidalgo, Levee District Commission president, said the district received a preliminary assessment for the National Weather Service in Lake Charles of what a Hurricane Isaac-type storm could mean for the parish levees. “Just on a preliminary basis, it’s not bad. The areas we’re trying to protect appear to be, some of them, protected,” Hidalgo said.
Regarding T. Baker Smith’s wave run up analysis, Kennedy said, “I don’t want to mislead anybody and say that this could change anything in the eyes of the corps. I think we’re doing this as our own investigation to give us an idea of what those design heights may be,” he said. He thinks the corps has gotten away from certifying levees for riverine events but certifies them, instead, for storm surge events, he said.
Hidalgo said the levee district wants to get actual data versus data where the corps looked at one spot and “painted” the whole area as being the same as the rest of the levee, so they asked T. Baker Smith to do the work because of its experience doing this type of modeling.
The levee district also approved a letter/permit of no objections for Shell Pipeline Co. to do construction work under the Wax Lake Outlet East and West levees. The special meeting was called because Shell wanted to expedite the signing of the permit so they could go ahead and begin work to replace the pipeline. Shell paid for the cost to hold the special meeting, Matte said.
The levee district is still in discussion with the parish, the City of Morgan City and the Town of Berwick regarding the district’s proposed cooperative endeavor agreement between the district and other entities to act as the single voice for the levees, Matte said.
“One of things the parish is looking is to get some indication of when we may be able to move into a (project partnership agreement), and, therefore, relieve the parish of some of their responsibilities,” Matte said. Matte said there will be financial commitments the levee district will be responsible for in the project partnership agreement with each entity as part of the cooperative agreement with Morgan City, Berwick and St. Mary Parish.
The levee district rescheduled its regular April meeting to April 18, Matte said.
For the ongoing Franklin Canal project, the levee district is also posting authorized personnel only signs. There has been an issue with four-wheelers on the levee and fines are being considered, said Nicole Cutforth of CB&I civil engineering firm.
There has also been an issue of fishing boats speeding along the levee, she said.