Officials investigate possible damage to Lake Manatee's dam

EAST COUNTY — As Bruce MacLeod watched construction crew members drill into sections of the Lake Manatee dam last week, he looked a bit worried.

As the superintendent of Manatee County’s Lake Manatee Water Treatment Plant, MacLeod closely monitors the condition of the barrier every day.

The structure, which provides drinking water to more than 300,000 residents in Manatee and Sarasota counties, is about due for repairs, and MacLeod hopes they will be minor, if needed.

About three weeks ago, while reviewing notes from a regular inspection of the dam, MacLeod noticed that the report revealed irregularities near the dam’s spillway gate.

It appears there were spaces in a few areas in the dam’s clay core, which stops water from leaking downstream. If this core becomes compromised, it could prevent the structure from regulating the amount of water that flows through the dam.

The worst-case scenario is this could result in spillage, flooding 18 homes located downstream from the dam’s location on Waterline Road.

MacLeod hired engineers to investigate the potential problem.

“It’s serious enough that we’ve designed a fix, but we’re just taking precautionary measures right now,” MacLeod said. “It’s better to be safe.”

On Feb. 18 and Feb. 19, individuals working on site at the East County structure conducted coring techniques — accessing the heart of the dam by drilling into different areas of the core and lowering cameras into the holes.

The images captured below the surface are displayed to engineers in Tampa in “real time” and will be compiled and presented to MacLeod this week.

The photographs will reveal whether the soil protecting the core on the upstream side of the dam is loose — and how big of a fix is required.

If the soil is loose, water has the ability to seep through and reach the core. In turn, the core would start to erode and fail to prevent the excess flow of water. Without controlling how much water flows out of the dam, which relies on Lake Manatee as its primary source, flooding can occur.

Should the core have eroded areas, MacLeod has a plan.

Engineers will fill the spaces with concrete to seal the holes and prevent further stress on the core. Costs are contingent upon how many areas need to be filled and how much cement is needed. However, repairs could cost millions of dollars.

MacLeod said the dam is about due for some repairs. He estimates that a dam often needs some sort of repair by its 50th year. The Lake Manatee dam is 48.

If the dam requires repairs, MacLeod plans to have the first stages of the remedy to the core problem in place before the rain picks up in the late spring or early summer months. He predicts the work will take about two months.

“We’re lucky we found the problem when we did,” MacLeod said. “It should be good for another 50 years, after we make the needed repairs.”

TEST PREPARATIONS
To conduct the coring test last week, Superintendent of Manatee County’s Lake Manatee Water Treatment Plant Bruce MacLeod said the dam’s water level had to be lowered from 40 to 38 feet above sea level, to put less pressure on the dam as a precaution.

Heavy rains also have contributed to the pressure on and damaging of the soil at the dam’s core, MacLeod said.

Rainfall adds to the amount of water in the dam, which comfortably stores water at up to about 40 feet above sea level, before spilling over onto designated rocks and spill off areas. Once the water level returns to normal, and inches back off the land, it takes soil with it. The soil circulates back into the dam, causing erosion.

“Think of it as the water rushing over your feet at the beach,” MacLeod said. “Once it pulls back, your feet start to sink into the sand; that’s what’s happening here.”

BY THE NUMBERS
5.9 billon — The number of gallons the dam can hold
1 — The number of miles the dam measures
18 — The number of homes downstream from the dam
40 — The number of feet the dam’s water is above sea level
300 — The number of cubic feet per second the dam releases to go from 40 to 38 feet above sea level
1800 — The number of surface acres of a full dam

DID YOU KNOW
• The dam provides drinking water to 300,000 people in Manatee and Sarasota counties.
• The dam was built in 1967.
• The Lake Manatee dam does not conduct electricity.

Contact Amanda Sebastiano at [email protected].