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The River Environment Classification System (REC) is a 'controlling factors' approach that has been developed for national-scale classification of New Zealand rivers (Snelder and Biggs 2002). It explicitly accounts for the network spatial structure of rivers and classifies individual sections of the network according to large-scale characteristics of the upstream watershed and smaller-scale characteristics of the network section that control fluvial process (Figure 1). A reason for the weakness of many existing landscape classifications, which also use landscape scale factors to delineate regions of distinctive ecological character, is that they fail to adequately represent this network spatial structure of river systems.

REC was originally developed for river management applications in New Zealand, and we are looking to examine its applicability to US waters. Once technical issues related to datasets and differing landscape attributes are addressed, we hope to produce a classification that better discriminates patterns in physical (e.g., hydrology and water quality) and biological characteristics. This classification would provide a more rigorous spatial framework for river management, and would also improve on existing methods for defining reference conditions and diagnosis of biological impairment in watersheds. More specifically, we expect that REC will assist in the following regulatory and management areas:

Selection of restoration targets. In narrative TMDLs and other restoration actions, REC may be used to objectively select reference conditions to establish desired endpoints by looking for stream segments with appropriate unimpaired classifications.

Identification of at-risk waters. Based on stressor analysis, stream classifications that show a higher susceptibility to impairment or degradation can be cataloged, and segments with these classifications can be flagged for more careful use of resources and protection under the antidegradation clause of the Clean Water Act.

Assessment of impairments. In the absence of a complete monitoring census, the predictive capabilities of REC may be used to estimate water quality or biological characteristics for all unsampled river segments whose classifications match to segments with data. Similarly, REC might be used to estimate sets of unsampled river segments and catchments with a high probability of impairment and deserving of 303(d) listing.

This paper includes a brief overview of landscape classification theory and a discussion of the details of REC's classification approach. We also review some of the results from New Zealand applications of REC, and consider the steps necessary to evaluate REC's usefulness as a discriminator of biological characteristics in US river ecosystems. Finally, we look at how REC may provide improved understanding of river management, identification of at-risk waters, and development of site-specific criteria for narrative TMDLs.

Document Type: Research Article


Publication date: January 1, 2004

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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