Indian Trail Improvement District supervisors gathered with residents and ITID staff for a drainage workshop Monday where they heard from South Florida Water Management District representatives as well as former ITID engineer Jay Foy.
ITID officials organized the meeting to listen to ideas on how to prevent flooding such as what occurred during the deluge from Tropical Storm Isaac last August.
SFWMD officials presented plans and alternatives for a new berm to separate The Acreage from the J.W. Corbett Wildlife Management Area. The existing berm was said to have been in danger of breaching water into The Acreage during the flood, which drew the attention of Gov. Rick Scott, who put $8 million in his proposed 2013-14 budget to reconstruct the berm.
John Mitnik with the SFWMD’s Engineering & Construction Bureau said his department is going through an evaluation of alternatives for its levee improvement project to see which one has the most promise.
“So far we have completed a topographic survey of the area, both along the existing berm as well as into the southern portion of the Corbett area,” Mitnik said. “In addition to that survey, we have also conducted some geotechnical borings along that route to be able to support the design of the new levee.”
Considerations as specific conceptual designs are examined include safety, the impact to the wetland and other environmental considerations, complexity of construction, the cost, the amount of seepage that comes from Corbett into ITID and the impact of any of the alternatives on that amount of seepage.
The idea that has received the most discussion is a new levee that would be constructed 150 to 220 feet north of the existing levee inside the wildlife management area. The proposal would include a 15-foot maintenance “bench” between the existing berm and the new one. Another option would be to eliminate the maintenance bench and move the new berm closer and incorporate it with the existing berm, which would encroach less into the management area.
“We’re going through the different alternatives, comparing them against the criteria to see which alternative has the most promise,” Mitnik said. “We’ll be doing that over the next couple of months.”
Mitnik added that another public meeting is scheduled for Friday, April 26 at the SFWMD headquarters.
Martha Musgrove, representing the Florida Wildlife Federation, said that Corbett is public land that the federation helped assemble using taxpayers’ money. “We object to any use of Corbett and the destruction of wetlands within Corbett,” she said. “They are a vital part, an integral part, of the Corbett system.”
Musgrove said the federation does not object to the berm project itself but that, after consulting other hydrologists and engineers, did not believe that the levee project would provide the protection some people would think because so much of the water flow is through groundwater.
Musgrove also pointed out that ITID has authority to condemn as much land as necessary to remain within the existing berm footprint.
ITID Supervisor Michelle Damone said that ITID has records that show Corbett holds its water at higher levels than it is allowed to by the SFWMD.
“They have continuously done this through the years,” Damone said. “Most recently, our engineers wrote them a letter warning them that if we ever had a storm of this magnitude, it would jeopardize flooding our homes in The Acreage. What we feared could happen, happened. A storm of that magnitude came in, and waters were not drained properly prior to the storm.”
Damone said a balance is necessary between the needs of residents and the need to protect wildlife through the dry season.
“They’re trying to do what they can for the wildlife, and I love that we have the Corbett there, but we have to find a balance where Corbett can exist… and at the same time we have to protect our homes,” she said.
Foy, ITID’s former engineer, gave a hydrological description of ITID, explaining that most of his comments would be about the M-1 Basin because it is the largest portion of ITID and has the most restrictive discharge allowance. “That doesn’t mean the M-2 Basin or other areas don’t have issues,” he said.
Foy described the M-1 Basin’s characteristics, explaining that the southeast corner of the basin has more canals because it is the lowest part.
“The center is one of the highest in Palm Beach County,” Foy said. “I always get a little irritated when people make the comment, ‘You build out in the swamp, you deserve what you get,’ which is absolutely wrong. We have water control elevations that are higher than other areas.”
Foy said the current level of service adopted by the district for a three-day, 10-year storm with 10 inches of rain is to be able to get water levels down in the canals three days after the storm in order for the lots to drain.
“Obviously, Isaac had much more than that,” he said, explaining that 5 inches of rain raises the canal levels about 3 feet.
Without storage, under the current quarter-inch of daily discharge, it would take The Acreage 40 days to get rid of the water from a 10-inch rain, Foy said. “Indian Trail starts flooding when there’s about 5 or 6 inches of rain,” he said.
The M-1 impoundment has storage almost equal to 1 inch of rain on the M-1 Basin, he said. “The impoundment you currently have is one inch,” he said, explaining that controlling flooding is a combination of discharge, storage and pre-storm drawdown.
Under ideal conditions, ITID has the ability to handle a 10-inch storm under its current discharge, storage and pre-storm drawdown capability, Foy said.
“What do you think 7 inches of rain will do to you when you’re completely full already?” Foy asked. “You saw it.”
If ITID decided to change its direction for a 10-inch storm to 15 inches, it would need storage for 5,000 acre-feet and 1.25 inches of discharge per day, he said.
“The 5,000 means not at Palm Beach Aggregates, not at the C-51 reservoir assuming they are flooded,” Foy said. “If you’re talking about 15 inches, you’re talking about horrendous, costly design.”