Flood mitigation requires care

The Hudson Valley was hit hard by repeated flooding over the past few weeks. Homes, businesses, farms, roads and bridges all were badly damaged by near-record floodwaters. Now we're hearing calls to take action to prevent damage from future floods, and in particular to dredge or hem in streams with walls and levees.

Although these projects seem like common sense, centuries of similar responses have caused large and long-lasting ecological damage, wasted money, and ultimately failed to reduce flood risk — or even made it worse.

As taxpayers and owners of the natural resources in and around these streams, we should ask four questions about flood-control projects before any equipment is put into the stream.

What is the problem?

It may seem obvious that flood damage is caused by a badly behaved stream. In fact, flood damage can result from many factors, including severe weather, building in floodplains, streams that are blocked or filled with sediments, too many impervious surfaces (parking lots, houses) in the watershed, and alterations to the stream channel itself (channel straightening or levees, for example). All of these probably contributed to recent flood damages. Unless the causes of damage are correctly diagnosed, it is unlikely that effective treatments for reducing flood damages can be prescribed. For example, dredging a stream channel won't prevent flood damage that arises from putting a building in harm's way on a floodplain.

Will the treatment be effective?

Just as in medicine, different treatments are available to reduce flood damages, which differ in effectiveness, cost and severity of side effects. A treatment should be pursued only after an analysis shows it will actually reduce flood damage, is worth the money, and won't cause unnecessary ecological or property damage. For instance, if flood damage results from a channel that has filled up with sediment, treatment might consist of controlling erosion in the watershed, removing sediment from the stream channel, or both. If careless land use is filling streams with sediment, simply removing sediment from stream channels isn't an effective long-term treatment any more than one-time liposuction is an effective treatment for chronic obesity.

Does the treatment have harmful side effects?

Some of the treatments that have been proposed for local streams are worse than ineffective — they may actually increase flood damage. Treatments such as channel straightening and levee building often make flooding worse downstream and can accelerate bank erosion for miles both upstream and down.

Projects may cause severe ecological damage, too. Streams and rivers are complex and sensitive ecosystems, and inept flood-control projects can cause ecological damage that lasts for decades and extends miles beyond the project area. It is therefore essential to assess the likely ecological consequences of a project and to choose a project design that minimizes damage.

For instance, I've heard people suggest we need to remove boulders, logs and other "obstructions" from our streams. What these people call "obstructions" a trout would call "habitat."

Is it worth the money we'll pay?

Stream improvement projects can be expensive, and you and I are paying the bills, so it's important to know that we're getting our money's worth. How often will treatments like dredging have to be repeated? Is the proposed treatment really the cheapest way to reduce flood damage over the long term? Especially in this time of tight budgets, we should demand that any public money devoted to stream improvement be well spent.

It is surely a good idea to look for ways to reduce future flood damage in the Hudson Valley, and some of the solutions that have been suggested seem to be common sense. However, a long, sad history shows that well-intentioned "seat-of-the-pants" stream management in North America and Europe has wasted billions of dollars, badly damaged ecosystems, and actually worsened flood damage in many cases. We and our streams deserve a more careful approach.

Cary Institute of Ecosystem Studies | Millbrook, New York 12545 | Tel (845) 677-5343

Privacy Policy Copyright © 2014