These 10 Ecoregions were created to support mapping and analysis for the Chehalis Basin Strategy Aquatic Species Restoration Plan (ASRP; original document can be found at https://apps.ecology.wa.gov/publications/SummaryPages/1906009.html).For the ASRP, the entire Chehalis Basin was divided into Geospatial Units (GSUs). These GSUs are relatively small areas primarily defined by being a watershed to either a first-order stream or a stream- or river segment. They are used to define inputs to the Ecosystem Diagnosis and Treatment model (EDT), which is a spatially-aware model primarily used to estimate the impact of interventions on highly mobile aquatic species, such as salmon.The Ecoregions in this dataset were created by combining the smaller GSUs into larger units with similar ecological, geological, and in particular hydrological characteristics. Drainage basins for large and medium river systems, like the Wynoochee, Satsop, Skookumchuck, etc. were preserved intact within single ecoregions. Smaller drainage basins, like the Johns and Humptulips rivers, were combined with other basins to make up larger Ecoregions.Primarily, the Ecoregions were derived to support the EDT salmon model, and the development of restoration scenarios (see 4.2.2.1 of the ASRP Phase 1 document). Questions asked at the Ecoregion level included species distribution, the relative value of different restoration measures, and priority actions for each Ecoregion.The Ecoregions were created by ICF International Inc. in January 2017. See the Chehalis Basin Strategy ASRP Phase 1 document (https://apps.ecology.wa.gov/publications/SummaryPages/1906009.html) for more detail on the derivation of these ecoregions and their use in supporting the ASRP.

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