Little Gunpowder Falls

Brian Eddy of Forest Hill watches as the Little Gunpowder Falls continues to rise along Greene Road in Fallston early Wednesday evening. (MATT BUTTON AEGIS STAFF, Patuxent Homestead / September 6, 2011)

Heavy rains Tuesday, Wednesday and Thursday led to flooding, road closures, the evacuation of Port Deposit, at least two swift water rescues in Harford County and warnings that expected water release through the Conowingo Dam this week could approach levels not seen since Tropical Storm Agnes 39 years ago.

The rains are expected to continue with flood warnings that are in effect through the end of the day and Conowingo Dam officials say they are expecting to open up to 50 crest gates by Saturday, which is likely to cause major flooding downriver.

As of midday Thursday, 32 of the dam's crest gates were open, according to Exelon Power, the dam's owner. By mid-morning, Route 1 across the dam was closed to traffic for an undetermined period. An Exelon spokesperson said the highway was closed so an additional crane could be moved into place on the dam.

The U.S. Army Corps of Engineers also announced Thursday morning it had sent engineers to dams along the Susquehanna in Pennsylvania and to Conowingo to monitor the flooding situation along the river. A news release from the corps said it has closed flood gates at several dams in New York and Pennsylvania in an effort to control downstream flooding.

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Opening 32 gates at the dam is generally results in flooding in Port Deposit on the Cecil County shore of the river. Town officials said Wednesday they were preparing for the worst and had already canceled this week's riverfront festival that was to feature an appearance by county music legend George Jones. Port Deposit issued a mandatory evacuation order that was to take effect at 8 p.m. Thursday.

At about 10:30 a.m. Thursday, Harford County began relocating swift water rescue teams to the Port Deposit area, according to emergency radio broadcasts.

Dam officials said in a news release Thursday morning they expect to open 50 of the dam's 53 crest gates before the weekend ends. During the flooding caused by Agnes in June 1972, all 53 gates were opened.

River flows are expected to peak on Saturday at 6 a.m., according to the release.

It is a rare occurrence when more than 40 of the 83-year-old dam's 53 gates are open at the same time.

Record river flows through the dam were recorded during Tropical Storm Agnes on June 24, 1972, according to the U.S. Geological Service, or USGS, when the river crested at 36.8 feet.

Flood stage generally starts at 23.3 feet, Scott Hurst, the chief of the Susquehanna Hose Company in Havre de Grace, advised members following a conference call with Exelon officials and other emergency officials Wednesday evening.

Hurst e-mailed members that flows reaching 32 feet are expected through the dam by Saturday, but could reach 36 feet. He said dam officials explained the height of the water is the most critical factor in flooding, not the actual number of crest gates that are open at the dam.

Havre de Grace experienced major flooding during Agnes, Hurst noted; however, in the spring of 1996, when 46 gates were opened at the dam, it had "very little effect on Havre de Grace, but Port [Deposit] got it bad."

High water in Havre de Grace

In Havre de Grace, the Susquehanna River was brown and swollen, overflowing its banks in many parts of the city.

Public works officials gave the go-ahead to close the entrances to Tydings Park at about 9:45 a.m. Thursday.

The water there was already well into the parking lot, which was blocked off with police tape.

Tidewater Marina in the downtown area was also flooded, and several other waterfront parks, including Jean Roberts, Hutchins and North Park, were underwater, Havre de Grace Police Cpl. Neil Crouch said around that time.

Water Street was also shut down because of flooding, as was the public parking lot behind the water treatment plan.

NeighboringAberdeen seemed to be faring much better.