Eastern U.S. officials watch dams in wake of historic floods

Dam safety officials in Mid-Atlantic and Northeast states are keeping an eye on dams along swollen rivers affected or threatened by flooding from days of heavy rainfall. Especially hard hit was the Wilkes-Barre area, where 200,000 residents were ordered to evacuate as a precaution in response to the rising Susquehanna River.

Levees protecting Wilkes-Barre held and the Susquehanna began receding early June 29. However, water continued to rise in parts of New Jersey and Pennsylvania. Rainfall totals of 10-17 inches were reported in some areas from June 24-28. Major flooding was reported in Maryland, Pennsylvania, and New York. Days of torrential rain followed by flooding were blamed for the deaths of at least 16 people on the Eastern Seaboard.

Authorities declared emergencies and ordered hundreds of thousands evacuated across much of New Jersey, New York, Maryland, and Pennsylvania, while buildings submerged, roads washed out, and rivers surged.

New York Gov. George Pataki declared a state disaster emergency June 28 in nine counties. In Pennsylvania, Gov. Edward Rendell declared a disaster emergency in 46 counties, authorizing state agencies to use all resources to help people affected by the storms.

Prompted by rainfall of historic proportions, dam safety inspectors with Pennsylvania’s Department of Environmental Protection were in the field performing inspections. The agency confirmed the failure of one low-hazard dam in Luzerne County, Mountain Springs No. 2 Dam. DEP recommended all dam owners, regardless of dam size, to inspect their dams.

In Montgomery County, Md., officials watched for the possible failure of a 65-foot-tall earthen dam at Lake Needwood, near Rockville. State and county engineers worked June 28 to plug a half-dozen small leaks at the base of Lake Needwood Dam, according to published reports. People in low-lying areas south of the lake were evacuated as a precaution. The Maryland-National Capital Park and Planning Commission owns and maintains the dam, built by the Corps of Engineers.

Exelon’s 512-MW Conowingo weathers storm

In southern Maryland, Exelon Corp. opened crest gates at the 512-MW Conowingo project (No. 405) to pass floodwaters downstream on the Susquehanna. Exelon spokesman Benjamin Armstrong said the run-of-river project was operating as designed and that the high flows did not pose a dam safety issue.

The river was expected to reach a peak flow of 440,000 cubic feet per second at Conowingo at about 11 p.m. June 29. Earlier that day, Armstrong said 23 of the project’s 50 gates were open. At peak flow, the company anticipated 26 to 28 gates would be open. Each gate can pass 16,000 cfs.

At this time of year, typically no gates would be open, Armstrong said. A typical flow of 20,000 cfs all would be passed through the powerhouse. In 1972, the project passed a record 1 million cfs.

When all 11 of the project’s turbine-generators are operating, a total of 88,000 cfs can pass through the powerhouse. However, two of the units are down for routine maintenance, meaning the powerhouse can pass a maximum of 64,000 cfs, Armstrong said.

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