Dam failure is defined as the sudden, rapid, and uncontrolled release of impounded water. Dam failure can occur with little or no warning and for one or a combination of reasons, including overtopping, seepage (water percolating through the dam and its foundation) and structural failure caused by earthquakes, sliding and slope instability, or faulty construction.
Franklin County is home to 2 Class I dams, the largest and most hazardous type of dam, and is impacted by 3 additional Class I dams to the north.
Hoover Dam, near Westerville, dams Big Walnut Creek to form the Hoover Memorial Reservoir and is owned and operated by the City of Columbus. It is 2,583 feet long and 85.5 feet high. The reservoir has a surface area of 3,373 acres and can hold 20.8 billion gallons of water. It supplies water for the entire northeast portion of Franklin County.
Communities downstream include Gould Park at 4 miles, Gahanna at 7 miles, Whitehall at 10 miles, and Columbus at 12 miles. Inundation is expected to be noticed in Circleville 30 miles downstream. Damage is expected to be extensive and would include many residential structures, state routes, local roads, interstate highways and businesses. Loss of life would be expected.
Julian Griggs Dam
The Julian Griggs Dam, owned and operated by the City of Columbus, is located on the Scioto River near Upper Arlington, 6.5 miles upstream of the Olentangy River confluence and 9.3 miles downstream of O’Shaughnessy Dam. The dam is a concrete gravity structure 983 feet long and 52 feet high at the maximum section. The reservoir is almost six miles long with a 1.2 billion gallon capacity. Dam failure could result in severe property damage with possible loss of life.
O’Shaughnessy Reservoir Dam
The O’Shaughnessy Dam, owned and operated by the City of Columbus, is located on the Scioto River in Concord and Liberty Townships in Delaware County. The dam is 4 miles upstream from Dublin, 9.3 miles upstream from the Griggs Dam, and 16.5 miles upstream from downtown Columbus. The Columbus Zoo is located on the east bank of the reservoir, near the dam.
The dam is 1,750 feet long, containing a central concrete masonry section of 879 feet in length and 84 feet high. The reservoir holds 6.3 billion gallons of water covering a surface area of 845 acres. In 1987, the City of Columbus installed a pair of hydroelectric turbines. They can only be operated when there is sufficient flow, so they can only intermittently provide power, producing up to 5 megawatts. Failure of the dam could result in severe property damage with the possible loss of many lives. Significant encroachments on the Scioto River floodplain, including residences, commercial establishments, and the Julian Griggs Dam are located within the first 15 miles downstream.
The Delaware Dam is located on the Olentangy River in Delaware County, 4 miles upstream of the city of Delaware and 32 miles north of Columbus. The project was constructed and is operated by the U.S. Army Corps of Engineers for the purposes of flood reduction, low-flow control for pollution reduction, water supply, and recreation.
The dam is 3 ½ miles long and 92 feet high. It controls a drainage area of 386 square miles through the use of five gated sluices and six 25 foot by 32 foot tainter/radial gates. The Delaware Dam is a unit in the larger comprehensive flood control plan for the Ohio River Basin. Dam failure would result in extensive property damage and possible loss of life in the many population centers downstream.
Alum Creek Dam
The Alum Creek Dam is located in Delaware County, between I-71 and U.S. 23, 12 miles southeast of the city of Delaware and 25 miles northeast of Columbus. It was built and is operated by the U.S. Army Corps of Engineers to reduce the flood hazard along Alum and Big Walnut Creeks, the Scioto River and the Ohio River.
The dam is 10,000 feet in length, with a maximum height of 93 feet. The spillway is located high on the right abutment with the raceway dropping off in front of it to the stilling basin below. Control is provided by three 34 foot by 25 foot tainter gates, supported by 8 foot wide concrete piers resting on concrete ogee sections. Dam failure would result in property damage with loss of life, as development continues to grow south of the lake.
For more information about dam failure visit: http://www.fema.gov/protecting-our-communities/plan-ahead-dam-failure