Manatee County makes water-wise investment

Manatee County Water Treatment Plant Superintendent Katie Gilmore walked across the Lake Manatee Dam and pointed to a concrete spillway on one side and Lake Manatee on the other.

It was a quiet setting.

Early next year, though, the scene will look much different as contractors are busy repairing the spillway and reinforcing the dam structure.

Manatee County’s water division has begun efforts to complete a second phase of repairs on the Lake Manatee Dam, which is more than 50 years old. The projected cost is approximately $17 million.

“This will extend the life of the dam for 50 years,” Manatee County Water Division Manager Mark Simpson said. “We can’t stress enough that reinvestment in the infrastructure is going to be required. While $17 million is a significant cost, the value it provides dwarfs the actual cost.”

Manatee County completed emergency repairs on the Lake Manatee Dam in 2014 to address  erosion issues. At that time, however, engineers inspecting the dam recognized future repairs would be needed.

The work had been scheduled for this fall, but the project was delayed as engineers further evaluated the dam, what repairs were needed and the best way to complete them. As a result, this second phase of repairs not only will correct erosion problems downstream from the dam’s primary spillway — a structure used in the controlled release of flows from a dam or levee into a downstream area — but it also will include repairs to the approach — the portion of the spillway leading to the dam from the lake.

To complete that repair, contractors will have to build a cofferdam, a watertight enclosure pumped dry to permit construction work below the waterline.

Bids for building the cofferdam likely will go out this month. Construction is expected to begin in April.

Construction of the cofferdam means the dam’s primary spillway will be out of service and will not be able to control releases of water during significant rain events, as it usually does. However, the dam has an auxiliary spillway on its northern bank that will be reinforced to better handle water overflowing it.

“It’s the same (water) flow down the river as if you had no dam at all,” Simpson said of the impact. “The dam is not a flood control structure. It’s to hold drinking water.”

Gilmore said water that normally would be released through the dam during a high-rain event will naturally spill over the auxiliary dam and into a field designed to handle the extra water. The property is county owned and there are no homes in the area.

She said the homes down river from the dam, which are usually notified when the dam releases water during rain events, should not be affected because the dam itself will not be opened and water will not be able to spill over it.

Water levels at Lake Manatee normally are kept at 40 feet during the dry season (October through May), but the new normal during construction will be 39 feet.

Simpson said the repair work required is more extensive than realized in 2014, and Manatee County has reserves designated for about 40% of the total cost for Phase II repairs. The dam has sufficient reserves to cover the remaining $10.2 million, but the money ultimately will be returned to reserves. Manatee County’s financial department will determine the best method for doing that, but it could take out a bond or other long-term financing mechanism that would be passed to utilities users, Simpson said.

The project is expected to be finished in February 2019.

Manatee County celebrated the 50th anniversary of breaking ground on Lake Manatee Dam in October 2015.