2017-04-27 / Front Page

Reservoir in dire need of new dike

$550K warrant to be decided at June 5 meeting
BY TIM RIEL


Town Engineer Mike Gray on the South Pond dam Tuesday afternoon pointing out the high watermark from 2010. Where the grass path curves is where the dam turns into the dike. 
PHOTO BY TIM RIEL Town Engineer Mike Gray on the South Pond dam Tuesday afternoon pointing out the high watermark from 2010. Where the grass path curves is where the dam turns into the dike. PHOTO BY TIM RIEL The town will ask voters to approve a warrant for $550,000 to protect the South Pond dam, which was built at the turn of the 20th century.

“We have to be responsible because this is our water supply,” Town Engineer Mike Gray said Tuesday morning during a tour of the property.

The town is tasked with securing the dam for a 100-year storm, which has an annual probability of 1 percent. Simplified, a storm of that magnitude would drop at least 9 inches of rain onto the island. Although it’s unlikely, Gray has witnessed the waterline just 1 inch from the top of the dam. That was during the springtime flooding of 2010.

“The threat is water spilling over the earth and eroding the dam,” he said. “That’s why we have to be proactive.”

To prepare for a 100-year storm, workers will bypass the dam across the southern section and fortify the dike that runs north along the west side of the 6-million-gallon reservoir. Both sections are made entirely of compacted earth.

According to Gray, workers will begin by excavating the current dike that is 8-feet wide and 500-feet long. They will then rebuild the embankment using riprap, which is a mixture of stones and rubble, with concrete blocks topping the new dike.

Although the bond question will appear on June’s ballot, the issue surfaced about five years ago after the state ordered the town to clear-cut vegetation along the dike. Because it’s considered a “high hazard dam,” the Department of Environmental Management also told the town to have the property inspected by civil engineers. A subsequent review by Pare Corporation found that the spillway could only handle a 2-year storm. The state is now requiring an overhaul of the abutment.

“We have no choice,” Town Administrator Andy Nota said. “This needs to be done.”

After receiving notice from the state, Gray initially planned to rebuild the dam and spillway, which would require heavy equipment and specialized labor. The preliminary cost was $750,000 and climbing.

“Rather than do all that, which would be very expensive, the engineers came up with a solution,” he said. “The spillway stays intact. The dam section stays intact. But we rebuild the dike section with armor.”

Because the dike will be about 18 inches lower than the dam, heavy rainfall will cause the reservoir to spill over the western edge into wetlands and eventually Dutch Harbor. Right now, water does top that side, but the dike embankment has become deteriorated because it’s only soil and grass.

According to Gray, equipment and workers from his department could provide the labor since the project doesn’t include digging concrete. If approved, the project will commence during the dry season when the reservoir is at its lowest point. That’s typically toward the end of summer.

“It’s simply earthwork,” Gray said. “We’re just removing the dike and rebuilding it. We have the means and methods to do that, so we can save the town some money.”

Although the town has to bond the project for liability reasons in case the water company collapses, utility customers are ultimately on the hook for the $550,000, Nota said. At the financial town meeting, however, all registered voters will have their say. According to Gray, about half of the town’s households use public water while the other half own wells and septic systems.

Gray said supporting this project should be an easy choice for residents. They only have to look back six months following the summer’s drought, when the town began pumping 300,000 gallons of water daily from South Pond to the 60-million-gallon North Reservoir. That resulted in two full reservoirs by April.

“This is a huge resource to the town,” he said. “We don’t want to lose it.”

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