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NWS: Isaac’s Valley deluge up to 4 inches
YOUNGSTOWN
The National Weather Service projects the remnants of Hurricane Isaac will dump 3 to 4 inches of rain over the Mahoning Valley over the next five days, but the U.S. Army Corps of Engineers said its lakes will be able to hold that water.
“We will be holding any additional inflows and storing water in our lakes” in an effort to restore them to normal levels, said Megan Gottlieb, hydraulic engineer and acting water management chief for the U.S. Army Corps of Engineers’ Pittsburgh District.
“There may be downstream flooding that our reservoirs cannot control,” she warned Friday, adding that the corps can only control water flow from rainfall behind the dams at its lakes.
“We’re expecting Isaac remnants to enter our area Monday afternoon,” she added.
The 3- to 4-inch rainfall estimate is for the corps’ Berlin, Kirwan and Mosquito lakes, with Shenango River Lake more likely at the lower end of that range, Gottlieb said.
Currently, Berlin, Kirwan and Mosquito are under drought watch, and Shenango is under drought warning, Gottlieb said.
Because of dry conditions, Berlin, Kirwan and Mosquito never reached their normal summer-pool levels this year, and they now stand below their normal winter-pool levels, said Daniel Jones, the corps’ public affairs chief in Pittsburgh.
The low water levels have presented underwater obstruction hazards for boaters and forced closings of boat launch ramps this summer.
Lake Milton, which is owned by Ohio, but whose level is regulated by the corps, will begin its autumn water draw down Tuesday, a month earlier than last year, Jones said.
Gottlieb said the drawdown there is starting earlier during this dry year to maintain downstream water flow and water quality.
“If we wait until October to start drawing down Milton, Berlin will be even lower,” Gottlieb added.
The corps plans to draw down Lake Milton, which is now several inches below its normal summer level, by about 6 inches between Tuesday and Sept. 15 to facilitate a noon to 4 p.m. Sept. 15 Wheels and Keels antique car and boat show at the amphitheater.
After Sept. 15, the corps plans to accelerate the lowering of Lake Milton, which it plans to bring to its normal winter level by Dec. 1. At Lake Milton, normal winter pool is 8 feet below normal summer pool.
Under an agreement between the corps and the state, Lake Milton must be maintained between Memorial Day and Labor Day at whatever level it was topped out at in the spring.
Jones and Gottlieb said sufficient water must be released from the dams at corps-regulated lakes to maintain adequate downstream river flow for three reasons:
To keep enough flow in the river so the water has sufficient dissolved oxygen to support aquatic life.
To avoid a concentration of pollutants in diminished flow that would impose an additional burden on downstream water supply treatment plants that get their water from the river.
To have sufficient river flow to dilute pollutants, including sewage treatment plant discharges flowing into the river.
In addition to maintaining downstream water quality, water released from corps-regulated lakes in the Mahoning and Shenango valleys and elsewhere helps maintain navigation depths in the Ohio and Mississippi rivers, Gottlieb said.
Jones said he is not aware of any boats running aground or being stranded in the Ohio River, where the corps strives to maintain an 8- to 9-foot navigation channel depth for commercial traffic by using its system of locks and dams and by dredging when necessary.