And it will flood again

By DAVID HULSE

HAWLEY, PA — Flooding can be expected along the Delaware but local officials say the levels and crests of April flooding didn’t jibe with official predictions.

Mayor Walt Conway of Delaware Water Gap Borough wanted to know why. He came to a May 25 informational workshop for public officials, sponsored jointly by the Delaware River Basin Commission (DRBC) and Pennsylvania Power and Light (PPL) Corporation, looking for answers. He listened to a New York City Department of Environmental Protection (DEP) engineer explain why the city’s dams could not provide flood protection, but could “attenuate” the flow to lessen the crest. He listened to a PPL engineer explain why Lake Wallenpaupack opened its spillway in the middle of the flood. He listened to a National Weather Service (NWS) hydrologist detail how the agency gave warning. He wasn’t satisfied.

He said he was told to expect a 1:00 a.m. crest on April 3, but the crest didn’t arrive until 4:30 a.m. and it was four feet higher than predicted. “Attenuation, mitigation…sounds good, but [the flooding] lasted longer,” he said.

“I appreciate your concern for clear, pure drinking water, but your precious drinking water is impacting me tremendously…. I’ve got a business with 500 employees threatening to move. We can’t have that. There has to be better control of the water…. There should have been better coordination,” Conway said.

Paul Rush, Director of the West of Hudson Operations Division for DEP, was one of six presenters who addressed about 75 state and local agency and elected officials at PPL’s Lake Wallenpaupack Environmental Center. Rush explained that the city’s Delaware system dams and reservoirs were designed and operated to supply about half of New York City’s drinking water. They have neither the release works to quickly release large quantities of water, nor the mission.

But the dams did provide some relief, he argued, in that they attenuated or delayed the flooding since their spillways released water at a slower pace than new rainfall entering the watershed behind them.

PPL’s Gary Petrewski reported that despite the decision to release water during the flooding, the dam at Lake Wallenpaupack reduced downstream crests as the lake inflow greatly exceeded the combined 8,000 cubic feet per second releases at the dam and powerhouse. Criticized for failing to make timely notifications before the release, Petrewski said PPL has updated its notification policy.

Rush noted that one of the city reservoirs, Pepacton, had instituted a storage-reduction program last winter as a flood-protection measure, leaving empty the storage area which represents about one-half of the unmelted snow pack in Pepacton’s drainage area. The program ended on March 31, days before the flooding, but Rush said the amount of new rainfall input from late March and early April storms would have refilled and overflowed the dams anyway. He provided figures to show that similar programs at the Cannonsville and Neversink reservoirs would have similarly been ineffective against the 100- year flooding.

System not designed for emergency action

In any event, the system’s administration cannot react quickly to changing weather conditions, since the five parties to the 1954 Supreme Court decision, which essentially licensed the city’s withdrawals from the basin, must agree upon releases.

Since the basin is also subject to drought, deferring the system’s storage obligations increases the risk of supply if flood prevention programs are implemented at multiple locations, he argued.

New York, and New Jersey attended the meeting.

The inability of water-supply dams to provide flood protection was further highlighted by a U.S. Army Corps of Engineers presentation on corps’ flood-control dam projects in Pennsylvania. Locally, the Jadwin and Prompton dams lowered flood stages on the Lackawaxen River in Honesdale by 3.5 feet and by two feet in Hawley during the April flooding. They prevented an estimated $3 million in damages and have saved $12 million since 1960, according to corps engineer Francis Cook.

Nelson Delameter, director of Delaware County, NY, Emergency Services, agreed with Conway. “Attenuation is a misconception,” he said. “You shave some off the top, but it doesn’t matter because the water stays higher longer.”

Delameter also agreed that the reservoirs could not “release on a hunch,” but argued that river flow and storm records exist back to 1933. With modern technology and computer modeling of storm events, “Can’t we predict refill capability better?” he asked.

But another participant argued that old patterns may be changing, given two major flooding events in the past eight months. “Are these events significant enough to change our thinking as to what constitutes a 100-year event,” he asked?

100-year flood is 1-in-100 chance

Peter Ahnert, Hydrologist in Charge at the National Weather Service, Middle Atlantic River Forecast Center said the term “100-year flood” is misleading because it leads people to believe that it happens only once every 100 years. The truth is that an uncommonly big flood can happen any year… There is a 1-in-100 chance that a flood this size will happen during any year.

“Perhaps a better term would be the ‘1-in-100 chance.’”

Ahnert explained that the combination of a wet season, followed by a lesser flooding event, and then major basin-wide rainfall has to combine to create a 100-year event. He showed archived NWS forecast data that analyzed flooding probabilities in long-term forecasting and narrowed the data down to warnings three days before the flooding.

All this weather forecast information is available on the Internet at weather.gov, while stream-flow information is available from the U.S. Geological Survey at usgs.gov.

Communications is another problem

Another participant noted that the NWS has difficulty getting warnings and watches to the public on the radio, since so few of the area’s stations remain in local ownership or even have staff on site. “We don’t know whom to call,” to get them aired, he said.

Sullivan County Legislator Leni Binder said a new level of weather alert is necessary since conservative NWS forecasts often don’t come to pass and are seen as “crying wolf.”

The warning about April flooding, she said, “was not sincere,” about “just how serious it was going to be. Somewhere there is a communications gap,” she said.

DRBC Executive Director Carol Collier agreed that the NWS system “needs tweaking.”

Collier said the DRBC’s Flood Advisory Committee met even as the flooding receded and approved 10 recommendations to help mitigate future flooding.

Recommendations included installation of additional precipitation and stream gages, correlation of gage readings with flood stages, improved flood modeling and development of web-based, graphical NWS flood-warning products. Also recommended was increased NWS, USGS, and U.S. Army Corps of Engineers funding for the development of flood stage forecast maps to be integrated with improved graphic-based-river forecasting.

The committee called for increased funding for pre-disaster mitigation programs through local planning efforts, an update of the 1984 Army Corps of Engineers basin survey and more federal money for flood plain land acquisition.

They called for updated Federal Emergency Management Agency flood-plain mapping and stronger regulation of flood plain development modernization funds to those municipalities where flood conditions have changed due to development and construction.

Finally, they found that “snowpack-based storage management programs for water supply reservoirs should be evaluated, while recognizing the limited-seasonal availability and marginal risk reduction offered by this type of flood mitigation. Evaluation of such programs must consider the supply risk incurred to the 1954 U.S. Supreme Court decree parties in their implementation. In the Upper Delaware River Basin, such programs require unanimous approval of the decree parties.”