Canal structure: What it can and can't accomplish

How the Franklin Canal flood control structure operates in tidal surges as opposed to rain events remains a work in progress.
That’s how St. Mary Levee District Executive Director Tim Matte explained it to the parish council Wednesday. He was asked to address the panel by Councilman Dale Rogers, in response to last week’s deluge of rainstorms.
“When the floodgate was originally envisioned there was no pump station involved,” Matte said. “The intention was to keep storm water, primarily, from entering the Franklin Canal, which would then spill over and cause flooding throughout the Franklin area.”
Pumps were later added when initial bids came in lower than expected and there was money left over. Two of the four designed pumps are in place, he said.
Matte said the levee district is authorized to operate and maintain the structure, but also has an agreement with the City of Franklin to do actual operation and maintenance in a joint effort. The district pays costs.
In a hurricane approach, with days’ notice in advance, procedures in place to give notice, close the structure, drain the canal via the pumps, and prevent storm surge, Matte said. “There have been a couple of occasions where we have operated the gates in response to high tides. Most recently that was in October, 2015.”
The week the first two pumps were installed, a notice of high tides was issued. There were people out at the beginning of hunting season. The district used social media, handbills on cars at the boat launch to notify people that the gate would be closed at a certain time.
Matte said in that event it was learned that there was a limit to the amount of water that can be pumped with only two pumps, which were unable to pump out water from the backside of the structure fast enough.
“You can’t just open the gate” at that point, he said. “There’s a certain differential between the inside and outside water that allows you to safely opening the gate, otherwise you have a risk of damage or just not being able to do it.”
He said a 40-foot opening in the gate will “move a tremendous amount of water compared to what you can do with the pumps.”
Installation of the last two pumps is ongoing now, Matte said.
The lowest section along the canal is at the old boat landing on Willow Street at 3.8 feet, highest is about 4.5 feet. In the recent storms, three days of high winds pushed water inland, then the rain came.
“We’re pretty confident that closing the gate would not have helped, it would have harmed that situation,” he said. “We would not have been able to get rid of that water fast enough.”
That’s why the gate was not closed, he said. “It’s based on our experience that there’s a limited amount of water we can move out with those pumps. It will still work with a storm surge.”
Rogers asked who makes the decision to open or close the gate. Matte said all decisions are made in conjunction with the City of Franklin by intergovernmental agreement.
There is signage at the boat landing, Matte said, used when issuing warnings that the structure will be closed. Shrimp boat owners inside the canal are also notified.
The district is considering modifications to the structure to relieve excess water behind the gate or in front of, depending on the circumstances.
“We’re probably going to learn more as the years go on,” he said. “It takes about an hour and a half to open or close the gate.”
In response to a question from Councilman Glenn Hidalgo, Matte said there is a Bayou Teche floodgate project which has been permitted by both federal and state authorities, but has not yet been funded. “We’re trying to secure the land rights,” he said.
The district could possibly close off the section of Bayou Teche north of the Baldwin Bridge behind what’s known as Victory Island. Then levees could be constructed and some form of structure put in place, Matte said.