Flooding: The good, the bad, and the ugly

By Ginny Privitar GOSHEN — An engineer advised local residents to ditch the traditional response to big storms, which has not helped flood-prone Orange County avert disaster.

At a recent informational session sponsored by the Orange County Water Authority, Julie Moore, a water resources engineer with Stone Environmental in Montpelier, Vt., reviewed several common “flood myths” that stood in the way of a more enlightened approach:

Myth: You can dig yourself out of a flood.

Reality: When you dig a deeper channel, it’s a self-fulfilling prophecy. The river will cut deeper, the banks will collapse, and more debris will dump into the river. Moore also cautioned against removing large boulders, which slow down the water and maintain the grade. There are important considerations as to how and when you clean out a stream channel.

Myth: Damage can be prevented by straightening streams and covering stream banks with rocks, a method called "armoring."

Reality: Armoring banks and straightening channels are short-term fixes that work for small and moderate floods, but don’t stand a chance in serious floods. They only move the problem downstream and deprive the bank of soil-anchoring vegetation.

Myth: Removing trees will prevent debris jams in the next flood. Fallen trees clogged culverts and hung up on bridges, causing widespread damage. In a post-storm survey in Vermont, tree loss was most abundant along waterways with narrow buffers only one to two trees deep.

Reality: A post-storm survey in Vermont, Moore's home state, found that it was the wide forested floodplains that stayed intact. Where there was a generous buffer of trees, the water slowed. Sediment and snagging debris that otherwise would flow downstream stayed in the buffer. Clearing stream bank vegetation also destroys fish and wildlife habitat.

Myth: The 100-year flood is behind us.

Reality: The Northeast is experiencing larger and more frequent floods, more than statistics have led the public to expect. There is no guarantee we won’t see another big flood this year.

Myth: Trying to put the stream back into its original channel will improve things.

Reality: Limit efforts to put the stream back. Streams that grow to many times their normal width and form new floodplains are trying to tell us something: this is the width needed to carry away floodwater, sediment and debris.

Myth: Sediment deposited on a floodplain after a storm should be scraped off.

Reality: Big chunks of debris can be removed, but the rest should be left alone.

Myth: Failed culverts and bridges should be replaced with ones the same size.

Reality: When streams expand to multiple times their original size, installing a larger culvert means the need to replace it will be less likely.

Moore said the viscous cycle must be stopped: First it's flood — then response — then “flood amnesia," which leads to further human encroachment on floodplains and river corridors. She urged the audience to “let the past be your guide.”

Stopping the cycle is critical for public safety, property protection, flood mitigation, good water quality, and healthy reserves of fish and wildlife, she said.

She outlined an action plan based on the best current knowledge of how rivers and floodplains work (please see related article).

“It is important to weigh the needs of the already-built and the natural environment," Moore said. "Look at a range of alternatives for the short and long term that will balance needs. Think about the watershed and your neighbors.”