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PETER AHNERT, HYDROLOGIST at the National Weather Service’s Middle Atlantic River Forecast Center, talks with Ted Rogers, also of the forecast center, at a regionwide flood meeting in Hawley, Pa. on Wednesday.

Floods Prompt
Planning Meeting

By Ted Waddell
HAWLEY, PA — May 27, 2005 – In the wake of the disastrous 100-year flood of April 2-5 that followed another 100-year flood seven months earlier, the Delaware River Basin Commission (DRBC) and Pennsylvania Power & Light (PPL) Generation sponsored a reservoir operations informational workshop at PPL's Lake Wallenpaupack Environmental Learning Center on Wednesday.
In introducing the workshop, Carol R. Collier, DRBC's executive director, said the workshop was geared to "looking at issues without political boundaries – for the second time in seven months, we've had to deal with evacuations, and we want to explain the flood warning system. . . . There's always room for improvement.
But . . . "There's no silver bullet," she added. "Floodplains do flood."
Weather Service Talks
Of Warning System

Peter Ahnert, hydrologist in charge of the National Weather Service's (NWS) Middle Atlantic River Forecast Center in State College, Pa., discussed the Advanced Hydrologic Prediction Service (AHPS) flood forecast modeling and inclusion of reservoir spills.
According to Ahnert, flooding is caused by several factors, including snowmelt, severe rainfall and/or tropical systems impacting an area.
"Our main mission is to issue weather forecasts to protect life and property," he said, noting the Delaware River Basin is comprised of 330 miles of the Delaware River and encompasses approximately 13,000 square miles of watershed, the "largest east of the Mississippi."
Ahnert said 19 major flooding "events" have been recorded in the region since 1839, and in the year prior to the April 2005 flood, rainfall was about 25 percent above normal.
In explaining the term "100-year flood," he said it was more accurate to call such an event a "1 in 100 chance a flood this size will happen during any year – it's like rolling the dice."
"There's no reason why you can't have two ‘100-year floods’ back-to-back in a year," added Ahnert.
In the case of the April 2-5, 2005 flood, it was preceded by an abnormally wet period lasting for months and high river stages, followed by massive flooding (called a precursor flood event) that in essence set the stage for the second severe flood seven months later.
"Some hydrologists say it takes an unusual set of conditions that come together in an unusual sequence in an unusual time and place to produce a rare event like a 100-year flood," said Ahnert.
Sixteen days before the Flood of April '05 struck the region, the NWS river forecast center started issuing flood predictions and, as the expected rainfall increased, sent out updated flood watches followed by flood warnings.
Ahnert said critical pieces of reducing flood losses include flood proofing, acquisition of private property in floodplains, floodplain regulation and/or structural measures to limit/control flood damage.
"The National Weather Service estimates that flood warnings can reduce damage by no more than ten percent," he cautioned.
In the adjoining Susquehanna River Basin, the NWS figures the benefit-to-cost ratio of a flood warning system is approximately 12-to-1, in that for every dollar spent on establishing a flood warning system, "you get $12 in benefits.
“A flood warning system gives folks a way to get to higher ground and gives emergency managers lead time," said Ahnert.
Reservoirs Not Designed
For Flood Control

The Delaware River System is comprised of four reservoirs, three of which are in the Delaware River Basin: Neversink, Pepacton and Cannonsville, all of which were constructed to supply water to NYC.
The large earthen dams are about 200 feet in height and 1/2 mile in width.
Although in periods of heavy rain, water is spilled from the dams – thus acting as temporary pools, lowering flood crests – the reservoirs were not built for flood control.
"They are single-purpose reservoirs," said Paul Rush, director of the West of Hudson Operations Division for the New York City Department of Environmental Protection (DEP).
"They were built to supply water to the city, not as a way to release water over a short period of time prior to a [flooding] event."
Ronald E. Thompson, a surface water specialist with the U.S. Geological Survey (USGS), pointed out that the April '05 flood was the second highest in recorded history, with a peak crest of 24.80 feet measured on the Delaware River (4-3-05), second only to the Flood of August 19, 1955, at 26.40 feet.
The Continuing Dangers
Alan Tamm, a hazard mitigations officer with the Pennsylvania Emergency Management Agency (PEMA), didn't pull any punches when he talked about what happens if you build in a floodplain.
"You're going to get flooded," he said.
In calling for a flood warning system in the Upper Delaware region, Tamm said, "We need to have as much information in the hands of the public so they can make the right risk decisions and protect themselves."
During the public comment period in the aftermath of the formal workshop presentations, a DEC representative called for the Federal Emergency Management Agency (FEMA) to "fix their existing lousy maps" before reissuing them in a digitized format.
Leni Binder, Sullivan County District 7 Legislator and chair of the county's Public Safety Committee, called for a better local flood early warning system "so we can save lives – somewhere there is a communications gap."
"Your precious drinking water is going over the spillway and is affecting my town and my business," yelled Walter Conway, mayor of the town of Delaware Water Gap, an area hard hit by recent floods. He asked why the NYC DEP can't release water from the upstream reservoirs in times of flooding to reduce damage downstream.
Rush replied that any type of release from NYC reservoirs in the Delaware River Basin must be approved by a consensus of the signatory states as per the U.S. Supreme Court decree of 1954 that paved the way for the creation of the reservoirs 50 years ago.

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