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The 1999 work plan for the Massachusetts Water Resource Commission (WRC) directs an interagency committee to define a stressed river basin. The WRC has assumed this task in response to the large amounts of time and money regulators and project proponents must invest when trying to evaluate the potential environmental impacts of a project with limited background information on the natural resources of a site. In developing a definition of stressed basins the committee has produced an outline of the information which would identify an area as weak and an interim list of environmentally vulnerable (stressed) basins. The stressed basin classification is intended to flag areas which may require a more comprehensive and detailed review of environmental impacts or require additional mitigation. This information will speed up the process of project review for regulators and will help guide communities to other areas more suitable for a proposed activity.
This report summarizes the work of the committee and presents the general conclusions reached by the committee. It also includes more specific recommendations developed by Department of Conservation and Recreation (DCR) and EEA staff for future work.
- A definition of stress includes streamflow quantity, quality and habitat factors.
- A lack of adequate quality, biological and hydrological data has necessitated the development of a method to define quantitative stress which was applied at the major basin and major sub-basin level.
- A second method has been developed to determine quantitative stress for a tertiary or secondary sub-basin which can be easily applied on a site specific basis, but has not been applied statewide as part of the classification developed under the first method.
- The second method should be used to refine basin stress classifications for tertiary or secondary sub-basins wherever possible.
- The committee recognizes that there are quality and habitat stresses and strongly recommends that the interim methods be used only as a first cut to determine hydrological stress.
- The delineation of stressed basins on a large scale is only a relative determination based on a comparison of measurements for Massachusetts' rivers.
- The downstream gage data is not a good indicator of the condition of the entire basin. Headwater streams may be stressed even though the downstream data indicates no problems.
- The delineations are intended for highlighting areas needing further study and for defining mitigation for potential projects. Delineations are not intended to be used in any other way.
- The flow values used as criteria to define stressed basins are relative values and are not related in any way to habitat needs.
- The basin method using the stream gage data delineates rivers with low flows, relative to other basins, but does not indicate whether the cause is natural or man-made.
Definition of Stress
A stressed basin is defined as a basin or sub-basin in which the quantity of streamflow has been significantly reduced, or the quality of the streamflow is degraded, or the key habitat factors are impaired.
- Quantity: A significant reduction in streamflow is defined as a decrease in key low and high streamflow statistics. Low flows in most of Massachusetts reflect ground water levels and are a good indicator of the health of a system. Reduced low flows can impact aquatic habitat and water quality. In addition, low flows are often the first indicator of environmental impacts. However, where flood skimming operations or dam regulations occur, reductions in high flow statistics can be also be significant.
- Quality: A degraded water quality is defined as water in a stream that does not meet surface water quality standards.
- Habitat Factors: A degraded habitat is defined as a river reach in which key habitat factors, such as temperature, quality, cover, substrate and accessibility, necessary to sustain a biologically diverse community are degraded. The stress can be due to a lack of streamflow, quality degradation, presence of dams, channel modifications, culverting and other factors. Indicators of stressed habitat include the absence or degradation of a target fish or other aquatic community or the absence of the ability of fish to move between multiple habitats necessary to their life cycles. Factors that limit movement include lack of flow, or reaches with no flow, and the presence of dams or other restrictions that prevent passage.
This information provided by the Water Resource Commission.