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A Dualistic Stream Classification System for Oregon: In Support of a Stream Compensatory Mitigation Framework
Citation:
Nadeau, T., J. Wigington, R. Comeleo, S. Leibowitz, R. Brooks, S. Patil, AND D. Sobota. A Dualistic Stream Classification System for Oregon: In Support of a Stream Compensatory Mitigation Framework. Presented at American Geophysical Union (AGU) Fall Meeting, December 03 - 07, 2012.
Impact/Purpose:
Presentation of the described work--development of a stream/watershed classification system for Oregon in support of a stream mitigation framework--and attendance at the AGU Fall meeting brings several benefits, including: 1) increased awareness of the advances made with this work to the larger scientific community, 2) an opportunity to receive constructive feedback and insights from others in the hydrology/classification community that could enhance the described work and related efforts, and 3) as with all scientific conferences, general networking and exchange opportunities for EPA scientists with the larger (and international) scientific community.
Description:
To meet the goals of the U.S. federal Clean Water Act (CWA) and Oregon’s Removal-Fill (R-F) Law, unavoidable impacts to jurisdictional waters, including streams and rivers, must be compensated for through compensatory mitigation under the CWA Section 404 and R-F permitting programs. Compensatory mitigation for impacts to the stream resource is not routinely required, as it generally is for wetlands, and that which does occur is often opportunistic or out-of-kind restoration (e.g. different stream type, wetlands) which does not provide functional replacement for impacts. As part of the effort to improve compensatory mitigation outcomes in Oregon, a stream classification system was needed to inform a more function-based, site level assessment of streams. To meet this need, we have developed a stream/watershed classification system for streams and rivers of various sizes, based in part on a hydrologic landscape classification system, addressing local assessment units, previously developed for Oregon. The system is hierarchical, expandable, and dualistic—providing information at both the local (reach) and watershed (integrative) scales. It recognizes the hydrologic and geologic drivers of stream functions, and meets several a priori criteria established to assure statewide applicability: (1) the same variables are applied regardless of geography to assure consistency across regions, (2) classification is accomplished through an automated GIS process, (3) classes do not require field verification, (4) data used are at appropriate resolution, and (5) classes are consistent with policy intent. Each stream type is defined by basic hydrologic and physical characteristics and determinants of flow regime, and reflects broad functional expectations. Because stream processes are highly influenced by watershed scale parameters, we developed watershed scale data layers to address such questions as annual water surplus availability, seasonality of surplus relea