2017-12-07 / News

Town delays work at South Pond dam

BY TIM RIEL

Repairs to the South Pond dam, which the state is mandating, will not begin until July at the earliest.

“There is a risk that one or two storms could impact our work area and cause damage to the remaining earthen dam,” said Mike Gray, town engineer.

Voters in June approved a $550,000 bond to secure the dam for a 100-year storm, which refers to a weather event with an annual probability of 1 percent. A storm of that magnitude would drop at least 9 inches of rain in a 24-hour period. Although that’s unlikely, Gray said he’s witnessed the waterline just an inch from the top of the dam, which was during the historic flooding of spring 2010.

According to Gray, the work needs to be performed during the dry season, which is July through September. Permits from the U.S. Army Corps of Engineers and the state coastal council, however, were approved later than expected. Because they weren’t authorized until September, Gray didn’t want to risk work being hampered by snow.

“It is important that the dam reconstruction be in the dry (season),” he said.

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

The issue surfaced five years ago when the Department of Environmental Management ordered the town to clear-cut vegetation along the dike. Because it’s considered a “high hazard dam,” the state mandated a property inspection by civil engineers. A subsequent review found the spillway could only handle a 2-year storm, which has an annual probability of 50 percent and would drop 2 inches of rain in a 24-hour period. The state is now requiring an overhaul of the abutment.

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 at least $750,000. To cut costs, however, Gray and the engineers determined a cheaper solution. The dam and spillway will remain intact, but workers will rebuild the earthwork dike and top it with concrete 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. The project is expected to commence when the reservoir is at its lowest point, which is typically toward the end of summer. The capacity is 6 million gallons.

The delay, however, does have one bright side. A resident who excavated his land approached the town about donating that soil. That earth, Gray said, can be used to rebuild the dike.

“It’s a great opportunity,” he said. “We can now stockpile that and save the money.”

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