Monday, October 3, 2011

Dave Gibson: River Management by Backhoe

“It is unfortunate that dredging has proceeded without any guidance from river experts who could provide natural stream dimensions based on a rapid assessment of natural bankfull, pool depth and riffle spacing. Measurements that could be done in a few hours and eliminate years of lost habitat,” stated Carol Treadwell, Executive Director of the Ausable River Association (ARA).

Natural stream dimensions? Bankfull? Pool depth? Riffle spacing? What is this, a how-to manual? A certain amount of assembly required? Or a level of river awareness and fluency that any floodplain community had better strive for?

It is understandable why the small streams and rivers in this heavily damaged region of the Adirondacks (twice this year) may be viewed as marauding aliens and enemies which require a serious “talking to” by backhoe. The human and community impacts of the flood are enormous and gut wrenching.

Yet, post World War Two we keep building in floodplains, whether we know we are or not. A favored textbook reads: “The average annual flood damage nationwide… has continued to increase… The use of flood-prone land continues to rise faster than the application of measures to reduce flood damages. This continues to be one of the foremost challenges to land planners – finding ways to control the use of flood-prone areas, and ways of requiring those who seek the advantages of use of floodable areas to assume a fair proportion of the financial risk involved in such use” (Water in Environmental Planning, by Thomas Dunne and Luna Leopold, 1978).

Carol’s quote was submitted for a news release issued this week by a coalition of concerned organizations and individuals who live in these communities, along with a letter to Governor Cuomo seeking an end to floodplain management by bulldozer, and a meeting to assess how best to respond to the altered nature of these waterways in ways that are mindful of people, property, stream health, aesthetics and tourism on which so many of these towns and Essex County depend.

Carol denotes an apparent lack of “river experts” and related oversight of the heavy earth moving equipment moving about our region’s streams during the Governor’s month-long emergency authorization. The Ausable River Association has spent years studying the Ausable. Similarly, the Boquet River Association on the Boquet. NYS Department of Environmental Conservation and Adirondack Park Agency know something about the behavior and morphology of rivers and floodplains. NYS DOT has environmental experts who know how to manage highway rights of way without taking a proverbial two by four to the environment. So, where are they? It was good to read that the Essex County Board of Supervisors is calling on these experts to help them assess and, if necessary, adjust the in-stream work as may be necessary. Governor Cuomo should have had his environmental experts in the field overseeing any stream work a month ago.

Yet, our state agency experts and field managers at DEC, APA, DOT still seem unable to respond in a coordinated, effective fashion, despite the fact that the Emergency Authorization issued by NYS DEC on that fateful Sunday, August 29 states: “This Authorization hereby allows emergency work to occur in navigable waters, streams and wetlands regulated under Environmental Conservation Law Article 15 and Article 24. The work hereby allowed must be immediately necessary to address an imminent threat to life, health, property, the general welfare and natural resources. All work carried out under this Authorization must be conducted in a minimally invasive manner, consistent with the goals of the restoration work. Non‐critical work is not allowed by this Authorization. All work must be undertaken in compliance with the conditions below.”

The emergency authorization and all conditions for working in the rivers is found at the DEC website. Based on what Dan Plumley of Adirondack Wild has observed, many of these conditions are being violated every day, but this assumes that the equipment operators understand the conditions, and that DEC is on-site to explain them, which it appears not to be.

There is probably a strong difference of opinion whether the work to date has been “minimally invasive” and necessary to address imminent threat. At the same time, the workers in the streams and their supervisors are doing all they can with the information and resources at hand. Which gets me back to Carol Treadwell’s quote: “natural stream dimensions based on a rapid assessment of natural bankfull, pool depth and riffle spacing. Measurements that could be done in a few hours and eliminate years of lost habitat.”

What is she talking about? I return to and quote from Dunne and Leopold’s Water in Environmental Planning (1978). Rivers construct their own floodplains, laterally migrate, and deposit lots of sediment in the process. Over a very long process of movement the river occupies each and every position on the flat valley floor, with the river moving laterally by erosion on one bank and deposition on the other. That is the meander that rivers want to achieve as their way of expending energy most efficiently. In fact, really straight stretches of river (absent human channelization) are rare “and seldom does one see a straight reach of length exceeding 10 channel widths.”

Yet, the river does not construct a channel large enough to accommodate flood stages. The bankfull stage referred to by Carol “corresponds to the river discharge at which channel maintenance is most effective, that is the discharge at which moving sediment, forming or removing bars, forming or changing bends and meanders, and generally doing work that results in the average morphologic characteristics of (river) channels.”

The authors Dunne and Leopold continue: “It is human encroachment on the floodplains of rivers that accounts for the majority of flood damage. Because it is a natural attribute of rivers to produce flows that cannot be contained within the channel, the floodplain is indeed a part of the river during such events. It is therefore important that planners know something about these characteristic features, and thus possibly counteract to some degree the emphasis placed on flood-control protection works. More logical is flood damage prevention by the restriction of floodplain use.”

In short straight sections in between meanders, stream pools and riffles alternate in consistent ways due to the creation of gravel bars on the convex side of a meander. “The distance between successive bars averages five to seven channel widths.” The alteration of steep (over the riffles) and less steep water (over the pools) is characteristic of rivers, as is the fact that meanders are steeper than the average straight section. I think this is the “pool-riffle spacing” Carol is speaking of. She may be suggesting that in-stream work should seek to maintain this kind of pool-riffle spacing, and ensure that stream slopes are not severely altered.

The worst thing to do, according to Dunne and Leopold, is to severely shorten a river channel with consequent change in channel gradient. “An imposed change of river slope can cause an instability quite irreversible in any short period of time, and is the most difficult change to which a stream must adjust.” It appears this is exactly what heavy equipment operators did to Johns Brook, and may be doing to other stream sections.

The authors’ conclusions may be ones which Governor Cuomo, DOT, DEC, APA, and Essex County should pay particular attention to: “Among the potential costs or disadvantages accruing from channel modification are: 1. Channel instability or effects of channel readjustment to the imposed conditions; 2. Downstream effects especially increased bank erosion, bed degradation or aggradation; 3. Esthetic degradation, especially the change in stream biota and the visual alteration of riparian vegetation, and of stream banks and channel pattern or form.”

Photos: Johns Brook, Keene, before and after channel dredging and grading by state-funded heavy equipment, photos by Naj Wikoff.

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David Gibson

Dave Gibson, who writes about issues of wilderness, wild lands, public policy, and more, has been involved in Adirondack conservation for over 30 years as executive director of the Association for the Protection of the Adirondacks, executive director of Protect the Adirondacks and currently as managing partner with Adirondack Wild: Friends of the Forest Preserve

During Dave's tenure at the Association, the organization completed the Center for the Forest Preserve including the Adirondack Research Library at Paul Schaefer’s home. The library has the finest Adirondack collection outside the Blue Line, specializing in Adirondack conservation and recreation history.

Currently, Dave is managing partner in the nonprofit organization launched in 2010, Adirondack Wild: Friends of the Forest Preserve.




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