Corps reservoirs prevent 2nd highest flood of record along Kiski River

#WaterWednesday

Corps reservoirs prevent 2nd highest flood of record along Kiski River

Headwater dams help cut Gordon’s flood waters in upper Ohio River Basin, Reservoirs drawing down to prepare for next storm

Recent operation of the district’s Conemaugh River Lake and Loyalhanna Lake dams east of Pittsburgh cut the crest of Kiskiminetas River by 17 feet, preventing the second highest flood of record.

Without the reservoirs, the Kiski’s crest would have risen five feet over flood stage to 30 feet instead of cresting at 13 feet. At that level, the Vandegrift, Pennsylvania area would have realized the largest flood event since 1936, before the region’s system of federal flood risk management reservoirs were built.

“Conemaugh saw the most dramatic spike, rising more than 65 feet in three days,” said Charles Kottler, hydraulic engineer, Pittsburgh District. “The storm water collected in Conemaugh alone would cover the City of Pittsburgh with five feet of water.”

The operation of the district’s 16 dams in the headwaters of the Upper Ohio River Basin also reduced the flood risk along other waterways as remnants of Tropical Storm Gordon dropped nearly five inches of rain in some areas over the weekend.

“Our water management team and dam operators continue to work around the clock to manage our reservoirs,” said Col. Andrew (Coby) Short, commander, Pittsburgh District. “These storms can change course quickly or intensify unexpectedly so we’ll continue to monitor and adjust as the forecast develops and the potential for additional rainfall exists.”

Operation of the Allegheny River and Monongahela River reservoirs cut the river crest by six feet at the Point of Pittsburgh. The Point crested at 27.08 feet, two feet over flood stage. Without Corps reservoirs, the crest would have been six feet higher, reaching around 33 feet. At that river level, three feet of water would have covered the grass at Point State Park and soaked the playing field at Heinz Field, and two feet would have stood on PNC Park’s infield.

Overall along the upper Ohio River, Corps reservoirs combined to reduce the river levels by five to eight feet, which would have sent the levels one to two feet over flood stage.

Corps reservoirs reduced crests on the upper Allegheny River by about three to four feet, which would have been at flood stage, preventing flood water from inundating areas of Franklin, Parker and Kittanning, Pennsylvania.

Corps reservoirs combined to reduce crests on the lower Allegheny River near the communities of Natrona and Sharpsburg by about four to five feet, which kept the river from going into flood stage.

The district’s Youghiogheny Dam reduced the severity of flooding along the Youghiogheny River – which reached 16.3 feet -- sparing communities such as Connellsville and Suterville an additional two feet of flood water.

Reservoir operations of Berlin Lake, Mahoning River and Michael J. Kirwan Dam and Reservoir cut the crest by seven feet at Leavittsburg along the Mahoning River in eastern Ohio.

Crests on the Mahoning River were reduced by seven feet, which would have pushed the river well over flood stage. Leavittsburg would have gone seven feet over flood stage to 16 feet, instead of cresting at nine feet. Youngstown would have gone three feet over flood stage to 17 feet, instead of cresting at 10 feet.

Currently, the district is releasing water to create flood storage space in the dams to capture potential runoff from incoming storms. The Corps cautions residents that rivers will remain artificially elevated and fast as the district discharges from its dams.

When heavy rains hit, Corps reservoirs minimize flooding by capturing precipitation that falls in one-third of our district boundaries. The district releases that excess water after the flood crest passes to regain flood storage capacity for the next storm.

To date, Corps reservoirs have prevented an estimated $36 billion in damages in the upper Ohio River Basin.

During dry times, up to 80 percent of the water that passes by the Point of Pittsburgh comes from Pittsburgh District reservoirs. This flow augmentation sustains water quality and allows industry to operate, public water supply and sanitary sewer systems to function effectively, and the environment to thrive.

To date, the Corps has not received reports of any damage to the 42 federally built, locally operated flood control projects which are typically comprised of levees, channels and flood walls. These projects have returned more than $20 in flood damages prevented for every dollar invested.

This video was originally published on our Facebook page on September 12, 2018.