Researchers studying Vt. stream recovery
CONCORD, N.H. (AP) -- Dartmouth College scientists studying the aftermath of Tropical Storm Irene in Vermont hope their work will help communities both predict and plan for future hazards.
Immediately after the 2011 storm, geography professor Frank Magilligan and earth sciences professor Carl Renshaw used a National Science Foundation grant to conduct a rapid damage assessment. They are now a few months into a three-year, $345,000 grant to study the storm’s longer-term effects, particularly in areas where overflowing streams washed away roads and houses.
Many communities found themselves ill-prepared for the storm, which knocked out hundreds of roads and bridges in the state, damaged or destroyed more than 700 homes and left some towns stranded. Flooding moved whole sections of rivers and streams, gouging out roads and farm fields. In some cases, huge piles of gravel were deposited in other locations.
"Irene was a wakeup call for them," Magilligan said.
Using a combination of their own observations, aerial photography and data from remote sensors, the researchers are developing faster and more accurate assessment techniques that can be used to pinpoint potential trouble spots along streams. The goal is to give communities tools they can use to make scientifically informed planning decisions, rather than make recommendations, Magilligan said.
"We’re not going to go to town managers and say, ‘Here’s what you have to do,"’ he said.
Kevin Geiger is a senior planner with the Two Rivers-Ottauquechee Regional Commission, which serves as technical staff for towns in planning, zoning and emergency management. While many towns have flood maps from the Federal Emergency Management Agency that give a good idea of the flood risk on major rivers, most of the Irene damage occurred on smaller streams, he said.
"There are streams that aren’t streams -- streams that had no water in them (before the storm) -- that split houses in half," he said. "You had streams you could step over carrying full-size trees."
From a scientific standpoint, the storm provided what Magilligan calls a "grand experiment" -- the opportunity to investigate what happens when a stream system faces a major disturbance. The storm was unprecedented in New England in terms of the disruption to stream channels, Magilligan said. The amount of sand and other material flung into the flood plain also was highly unusual, he said. Along some parts of the White River, more than a foot and a half of sand was deposited over an area more than 500 feet wide.
But beyond the erosion, the scientists also are concerned about how streams will recover. And in many cases, efforts to "repair and restore" streams with bulldozers and other heavy equipment actually did more damage than the storm, Magilligan said.
After the storm, the Vermont Agency of Natural Resources allowed people to work in streams with heavy equipment after receiving verbal approval from state river engineers. But critics have complained that the temporary emergency rules created a "lawless state" that had crews digging gravel from stream beds and piled boulders on riverbanks, damaging fish habitat and possibly worsening future floods.
A report published by the Vermont Fish and Wildlife Department concluded that a significant amount of stream channel alteration was conducted without proper consultation and oversight, or for reasons beyond necessary flood recovery. The agency said it could take decades for some fish and other aquatic populations to recover.
Magilligan, who describes some of the repair efforts as "falling somewhere between ad hoc and willy nilly," agreed. Streams generally recover from floods in five to 10 years, but he expects it will take much longer because of the additional damage caused by heavy equipment.
The scientists are comparing streams that were affected by Irene alone and adjacent regions where power equipment was used to reconfigure the stream channel. If the research demonstrates that recovery will take significantly longer in the latter, town planners may hesitate before using such equipment again, they said.
While not familiar with the details of the Dartmouth research, Geiger said any information that would help planners predict future problems would be valuable, particularly since the effects of a river and stream channels after one flooding incident often don’t become clear until the next one. For example, dredging after a major flood in 1973 may have contributed to the extensive damage from Irene, he said.
"They didn’t anticipate this as much as they should’ve," he said. "People tend to think it won’t happen again."
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