MANATEE -- One hundred cubic feet of water per second is being released at Lake Manatee as engineers continue to investigate erosion discovered at the Lake Manatee dam last week.
County officials announced Friday engineers had found areas of erosion underwater on the downstream side of the dam that could potentially compromise it if there were significant rainfall.
Engineers and consultants are continuing to investigate, taking samples to locate any critical areas in need of repair.
"We don't know if the core has been compromised at this point," Water Treatment Plant Superintendant Bruce MacLeod said.
Officials originally estimated it would take five to seven days to complete the investigation before a plan could be formed and repair work would begin. It now looks as if it may be the end of the month before engineers finish their investigation and can begin to put an action plan together, according to MacLeod.
"We think we can get the core of the work done by the rainy season," MacLeod said. "We don't want to create any concern for any of our downstream residents, and we want to keep our water supply."
Officials said they have begun to notify affected residents of the situation.
"With a dam there is always a risk," MacLeod said. "We want to minimize that risk."
To do so officials decided to release water into the Manatee River and lower the level of Lake Manatee to 38 feet, below its capacity of 40 feet. As of Tuesday morning the lake level was just over 39 feet.
With only one of three gates open, it should take about nine days for the lake to drop to 38 feet at the current rate of flow if it doesn't
rain, MacLeod said.
"It makes it a little more difficult to canoe because there is a flow," MacLeod said. "But you really aren't going to notice a difference."
Lowering the lake, however, will provide additional water storage in case of rain but it is necessary to do so slowly.
"We are trying not to get the tail water high," MacLeod said. "That's what we think caused the problem over decades."
Engineers believe what has happened over time is water being released would pull up soil.
"We are afraid it could be making its way back to the core," MacLeod said.
The core of the dam is composed of clay with concrete slabs on both sides for support.
To repair the critical areas, engineers may inject concrete down into those areas. Repairs could extend the lifespan of the 50-year-old dam another 50 years, saving money in the long run, he said.
"We have done really, really good maintenance on the dam," MacLeod said. "This is something that is happening subsurface."
Officials were first alerted of the situation last Thursday when they met with Carollo Engineering Inc. and AMEC Environmental and Infrastructure Inc. to review preliminary findings of a supplemental dam inspection. AMEC was subcontracted by Carollo for its expertise in the area.
The county began conducting supplemental inspections when anomalies were detected during an annual inspection a couple years ago.
As the investigative work continues, consultants are putting together a time line and hiring a company to handle repairs.
"We are finalizing an emergency action plan," MacLeod said. "We have been working on that since last summer."
Jessica De Leon, Herald reporter, can be reached at 941-745-7049. You can follow her on Twitter @JDeLeon1012.