Dam holds up under storm flow

Residents were warned about evacuation, but heavy rain didn't hurt Broad Creek Dam

October 16, 2005|By JUSTIN FENTON | JUSTIN FENTON,SUN REPORTER

Despite a voluntary evacuation alert on the morning of Oct. 8 amid a heavy storm, residents south of the Broad Creek Dam need not worry much about the prospect of floodwaters breaching the nearly 60-year-old concrete structure.

The storm that dumped 11 inches of rain on some parts of Harford County caused Lake Straus to rise considerably and caused more than five feet of water to rush over the dam that links it to the Susquehanna River.

As water began to trickle into the creek's floodplain and inch toward nearby roads, Darlington's volunteer fire department told residents they might want to consider leaving the area.

That warning was precautionary, said Nelson Allen, an engineer for the county's Department of Public Works, who said he donned an orange raincoat and visited area dams, including Broad Creek Dam, that morning to view water levels.

"When I was there, the dam was really in no danger or threat of overflowing," Allen said.

At its peak, water rushed over the dam at a height of five feet, one inch, said Dave Weisser, a senior ranger at Broad Creek Memorial Scout Reservation. The normal flow is about two feet above the dam, he said.

Maryland has 299 dams, ranging from the huge Loch Raven Dam -- a 100-foot-high concrete gravity dam -- to Broad Creek Dam, a slab of concrete that Weisser compared to a cinder block that water flows over.

Fifty-six are state-regulated dams regarded as "high-hazard," dams that could cause fatalities if breached. Three are in Harford County: Edgewater Village Dam on Otter Point Creek, Atkisson Dam at Winters Run Drive and Conowingo Dam on the Susquehanna River.

A breach of any would affect several hundred residents and several miles of roads.

Broad Creek Dam, owned by the Boy Scouts of America, regulates water flow from manmade Lake Straus into the Susquehanna in northeastern Harford County.

It was constructed in 1948 and was blamed for ending the status of the lower part of the creek as a prolific trout stream when the water becomes warmer.

When the storm hit, the dam was "well within" its designed capacity for handling storm flows, Allen said. The rain was brought on by the remnants of Tropical Storm Tammy.

The worst kind of storm, statistically, is called a "100-year" storm, defined by a rainfall event that has a 1 percent chance of occurring in a given year.

Most dams are designed for smaller "10-year" storms and have concrete-lined overflow areas, and the rainfall brought on by Tropical Storm Tammy was between a 10- and 15-year storm, he said.

justin.fenton@baltsun.com

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