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Relative resource values are determined by a GIS model that evaluates all of the areas within Portland's jurisdiction to determine if they provide significant natural resource functions. The model generates maps of riparian and wildlife habitat resources based on the presence of landscape features including streams, rivers, wetlands and other water bodies, floodplains, steep slopes, and vegetation. These features are associated with a set of riparian or wildlife habitat functions that are individually evaluated by the model. The relative resource value (high, medium, or low) of the resources is determined using a set of criteria developed from scientific studies and articles describing the role and function of riparian areas and wildlife habitat. For example, vegetated areas that are relatively close to streams and wetlands have been shown to be more valuable in terms of their ability to maintain healthy riparian function than vegetated areas farther from streams and wetlands. These areas generally receive a "high" riparian relative resource value due to their ability to provide microclimate functions (i.e., shade and temperature regulation), water quality functions (i.e., filtering of sediment and pollution), etc. An area farther from a stream or wetland would receive a lower riparian resource value because its ability to provide these same functions would be reduced. Once each of the individual riparian functions and wildlife habitat attributes of each resource are evaluated, a relative resource value is calculated based on both the number of and significance of functions provided by and attributes present in a given area. Each riparian and wildlife habitat resource is assigned a relative resource value of high, medium, or low. The wildlife values are then "adjusted" for all areas within a designated "special habitat area" (SHA). All areas within a designated SHA receive a "high" adjusted wildlife habitat resource relative value. The "combined" relative resource value is determined by comparing the riparian and adjusted wildlife habitat relative resource value of the resources. Those resources with either a "high" riparian or adjusted wildlife relative resource value are assigned a high combined relative value. Of the remaining resource areas, those with a "medium" riparian or adjusted wildlife resource value are assigned a medium combined relative value. The remaining resource areas are assigned a "low" combined relative value.
For more information, refer to the project website: http://www.portlandoregon.gov/bps/article/401358 |