Corridor Planning

Until the late 1990's flood control fixes were implemented on a project by project basis which often resulted in the creation of additional damage or the exacerbation of existing problems elsewhere in the watershed. In 1999, the Agency of Natural Resources (ANR) implemented a corridor planning process
and a fluvial erosion risk assessment and mapping process.

Since then, the Friends of the Winooski River has been an active participant in the development of corridor plans including the North Branch and its tributaries; Stevens/Jail Branch; Kingsbury Branch/Pekin Brook; and the entire mainstem from Montpelier to Cabot.

Understanding a River's Natural Tendencies Is Key to the Corridor Planning Process
Rivers and streams meander across their valleys. The amount of natural movement is influenced by the amount of water carried, the geology and soils a river flows through, and the shape and slope of its valley. Each stream channel is formed, maintained, and altered by the stream itself through the processes of erosion and deposition of sediment. Over time the stream establishes a channel shape that accommodates its spring thaws and summer droughts. The river is in a state of 'dynamic equilibrium'. The river is moving and changing, but generally in a slow and predictable manner.

The natural tendency of streams to adjust and move has been altered by human activities within the stream channels and their corridors as well as throughout their watersheds. Traditional land uses, river management techniques, and flood recovery efforts have involved the straightening, steepening, and down-cutting of rivers. For most Vermont streams, a combination of watershed, floodplain, and channel modifications over the past 150 years has led to major channel adjustments that are still happening today.

The river corridor planning process is a systematic approach to understanding the forces impacting a particular stretch of stream and how to best manage and protect a stream for multiple uses. Many of our traditional approaches to controlling streams such as dredging, straightening, armoring etc may alleviate the immediate issue at a specific location. However, they often have downstream and/or long term adverse impacts.

The goal of the river corridor plan is to recommend strategies and specific projects that will get us out of the expensive and destructive cycle we are currently in with our streams and rivers.


Results of Corridor Planning Process

There are two primary products from the corridor planning process. One is the river corridor plan which is a detailed document that describes the physical conditions of the stream. The other is a Fluvial Erosion Hazard (FEH) map. A river corridor plan provides background information on the river system and a detailed inventory and description of impacts or 'stressors' that are affecting the river's natural equilibrium. Background information includes geographic setting (land use history, political jurisdictions etc), geology and soils, hydrology (stream statistics, flood history) and ecologic setting.

Stressors include land use changes such as the loss of riparian vegetation, impervious surfaces, ineffectual storm water management, straightening, bank
armoring, dredging etc. Most importantly, the plan identifies strategies and projects that will help restore or maintain the stream's natural functions, protect human lives and infrastructure and protect habitat and water quality. The strategies and projects consider the background information and stressors, but are presented on a reach basis. A reach is not a fixed length but is determined by changes in land use, valley shape, etc.

Friends of the Winooski River uses these plans in determining where to focus our efforts within a particular section of the watershed. We may choose to plant riparian buffers to help slow bank erosion or we may work with municipalities to
mitigate erosion resulting from stormwater run-off.

Because the corridor plans and many of the other database resources available to communities to help them with planning are not organized on a town by town basis, the Friends will be piloting a Town Water Quality Action Plan in 2010 to help conservation commissions and other municipal entities incorporate water quality planning into their master plans.

The other main product of a corridor plan is the FEH map. While some flood losses are caused by inundation (i.e. waters rise, fill, and damage low-lying
structures), most flood losses in Vermont are caused by "fluvial erosion," Fluvial erosionis erosion caused by rivers and streams, and can range from gradual bank erosion to catastrophic changes in river channel location and dimension during flood events. One reason for the high cost and frequency of damages associated with fluvial erosion is Vermont's geography. Vermont is a mountainous state of narrow valleys and powerful, flashy rivers and streams. The climate is extreme, with intense rainstorms, deep snows, and destructive ice jams.

As noted previously in this article, many of the traditional practices of managing rivers simply lead to a cycle of implementing costly site specific projects that
often exacerbate problems and cause more damage. In recognition of this problem, the Vermont General Assembly directed the ANR to identify options for state flood control policy and a state flood control program. ANR developed the corridor planning process and the FEH risk assessment and mapping process.

The FEH maps identify the location and intensity of fluvial erosion hazards, as well as the area needed by a river to maintain equilibrium. Local governments can use the maps to define and adopt an FEH zone that will protect citizens and their property by mitigating (reducing or moderating) fluvial erosion hazards. Some fluvial erosion hazard mitigation activities can even lead to additional benefits that are harder to put a price tag on, like healthier rivers, enhanced recreational opportunities, improved aesthetics, and better wildlife habitat.

A number of towns in Vermont have adopted an FEH zoning ordinance including Northfield, Sharon, Stowe and Bolton. The Vermont League of Cities And Towns provides assistance to communities interested in pursuing these ordinances.

If you are interested, you can view existing corridor plans on the state's website. The Friends are also a co-leader on project to develop a guide to stream processes and corridor planning. The guide will be published in late 2011. For those of you who already know what sorts of issues exist within your community or on your land you can view the Friends Land Owner Assistance Guide to locate financial, technical and educational resources for improving the river's ability to determine its natural course.