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Selecting Reference Condition Sites: An Approach for Biological Criteria and Watershed Assessment

Douglas L. Drake and Rick E. Hafele

Oregon Department of Environmental Quality, Portland Oregon
2020 SW Fourth Avenue, Suite 400
Portland, Oregon 97201

This talk describes the approach the Oregon Department of Environmental Quality Watershed Assessment Section uses to select reference condition sites. The purpose of selecting reference condition sites is to establish an objective and systematic method for finding water bodies minimally disturbed by human activities for a given basin or region. The approach consists of using geographic information systems (GIS) and site specific information to characterize human disturbance. Selected reference sites are then used to describe "reference condition" for a specific region for the purposes of stream and watershed assessment.

Site selection utilizes a three step iterative process: 1) Pre-screening, which involves selecting a region, identifying the primary natural gradients, and using geographic information system (GIS) information and best professional judgment (BPJ) to identify watersheds with minimal human disturbance, and mapping candidate areas. 2) Site visits which are used to record reach level human disturbance and together with delineated watershed geographic information is used to score a Human Disturbance Index (HDI). 3) Site verification involves examining site results for any anomalies by reviewing the disturbance information and sampling data. While reference site selection is not based on in-stream conditions, final verification includes an evaluation of the biological, physical habitat, and water quality data for outliers that might indicate unidentified problems. Verification is completed with the assignment of a "site classification" grade.

Keywords: reference condition, watershed assessment, biological criteria, human disturbance.

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