Engineers gave updates on drainage projects in response to Tropical Storm Isaac flooding to the Indian Trail Improvement District Board of Supervisors last week. The projects involve rebuilding large pump stations and drainage pipes.
At the Jan. 21 meeting, Joseph Capra of Captec Engineering explained that the inverted siphon at the M-1 Canal allows water to go north to south underneath the West Palm Beach M Canal, and that the existing drainage head is located in the easement of the M Canal, which the City of West Palm Beach plans to widen in a few years. That will require ITID to move the drainage heads by extending them into the district right of way.
“They obviously want to widen this whole area of the canal,” Capra said. “As you can guess, that is going to cost you a little more money, and that’s the unfortunate part of the whole thing.”
The good news is that the new construction will increase the flow of the inverted siphon, improving the overall efficiency of the M-1 Canal, and allow the upper basin areas to drain more quickly, he said.
The problem is increased by the proximity of a Florida Power & Light pole that would require additional sheet piling to assure structural integrity. “Unfortunately, that all comes with a price,” Capra said.
Capra looked at the project in two different ways, two 6-foot-by-12-foot double box culverts at $2.6 million, and an 8-foot-by-12-foot single box culvert at $1.6 million, which he said would work but would also limit the district’s options in operating the system.
“This is obviously a major canal system for the district,” he said, explaining that the double box would give the district a backup system. “If we had to do any repairs or work in the box culvert, we could take one out of service and keep the other one in service. Do I think that’s worth $900,000? Probably not, but I just wanted you to be aware of the issue.”
He said it will be critical to do the work while West Palm Beach widens the canal, adding that they could start doing some work now but the cost would probably go down if it is timed closer to the West Palm Beach project.
Capra said an inspection had been done on the pipe a few years back, and the existing pipes built in the 1970s were fine, but explained that the City of West Palm Beach had indicated it would have to take the pipes out anyway in order to widen the canal.
Supervisor Michelle Damone asked what initiated the study, and Capra said the head loss problem was reducing the overall capacity of the M-1 Canal in The Acreage.
District Engineer Jay Foy said that after Tropical Storm Isaac, when the South Florida Water Management District finally allowed drainage through the lower M-1 Canal, the lower basin went down very quickly, within a day, but they could not get the water to drain quickly from the upper basin. “It just took forever,” Foy said.
Damone said she would prefer to start setting aside money now and do all the work at the same time as West Palm Beach.
“I think we would be better off waiting until they do some construction and piggyback off the cost of it,” Damone said, and Capra agreed with that idea.
Damone suggested that they come up with an estimated cost and put money aside to anticipate the project and do it along with the city’s project instead of paying for it all at once.
Supervisor Ralph Bair said he thought the district should not bear the full cost of the project.
“Why are we paying for most of it or all of it?” Bair asked. “We’re not moving [the canal], they are. That’s a lot of money for just an extension.”
Foy explained that West Palm Beach owns the right of way.
“It’s in their right of way, and it’s been there so long it’s a handshake deal, but it’s in their land and they can tell us what to do,” he said.
Foy said the new culvert heads would be a completely new construction into the district’s right of way, but that the new inverted siphon pipes would still be under the West Palm Beach right of way. He reiterated that the head loss would be reduced, thereby increasing drainage potential in the upper basin.
He explained that the new drainage would be a rectangular and smooth wall, rather than corrugated pipe.
Damone made a motion to receive and file the report, get reports on the estimated cost and set aside funds in a designated account. The motion carried unanimously.
Foy also reported on the planned improvements to Pump Station 2 just north of Orange Blvd. on the M-1 Canal.
Although the plan has been permitted by the SFWMD, Foy said the final drawings will not be ready until March.
“We don’t want to do this during the wet season,” he said. “This is just a status report to tell you where I’m at. The structural engineer has to design these. It’s going to be a sheet piling and concrete and sheet piling again, so the structural engineer has to design it so it doesn’t fall over.
Foy said the canal will have to be rip-rapped in order for the plan to work. A 9-foot diameter pipe is to be installed, in addition to the existing 7-foot diameter pipe.
Because of the change in design, he said it will probably cost closer to $500,000, rather than the $300,000 originally estimated. “We can’t really tell until it goes out to bid,” Foy said. “This is a specialized item.”