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Water quality conditions are the second criterion, after biodiversity, applied to our search for a study area within the Willamette River Basin. In using water quality as a criterion, the goal was not to find an area that was representative of the WRB in terms of water quality, but rather to find an area with fair to good water quality, potential for improvement, sensitivity to impact, and a high potential for future impact.
As with the other steps in the study area selection process, the project relied on existing data to select a study area. The themes available and relevant to assessments of water quality for the WRB were the Oregon Actual Vegetation map, from the Oregon Natural Heritage Program (Kagan ; Caicco 1992), the State Soil Geographic Data Base (STATSGO) map from the National Resources Conservation Service (NRCS), and a landcover/ landuse map derived from Advanced Very High Resolution Radiometer (AVHRR) data classified into 158 categories based on Normalized Difference Vegetation Index (NVDI). (Loveland 1991).
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With this data in hand, a cluster analysis, the grouping of a data set based on similarities of characteristics, was used to identify regularly occurring land pattern combinations, i.e. certain crop, soil and elevation combinations which occur together within the watershed. The most significant of these combinations were categorized into five clusters: riparian zones and flood plains, upland forest, low slope agricultural land, miscellaneous non-hydric soils, mid-slope forest and agriculture. Once identified, these clusters were then ranked for water quality, distinguishing areas with relatively good water quality and that had a potential for improvement.
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