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Thurston County is home to multiple watersheds and basins — areas of land where rivers, streams or other flowing surface waters converge. According to a Thurston Regional Planning Council (TRPC) report published this month, the health of the region’s basins improved modestly from 2016 to 2021.
This improvement marks a change to the trend of degradation that has persisted in recent decades, according to a county news release. Increased development can negatively impact overall basin conditions, but regional policies have helped protect healthy basins from these impacts.
“While the Thurston region grew by more than 20,000 people from 2016 to 2021, the impacts on overall basin health were limited,” Michael Ambrogi, TRPC senior planner, said in a news release. “In part, this is due to our region’s zoning and development regulations. New development is encouraged in areas that are already highly urbanized, helping to keep our healthiest basins healthy.”
TRPC’s Current and Future Basin Condition Assessment provides a big-picture overview of how changes to land cover have affected basin health, as well as impacts that are possible in the future. The assessment measures the health of 70 basins in Thurston County. These basins are fed by the streams and smaller drainage areas of the three major river systems in the county: the Deschutes, Nisqually and Chehalis rivers.
TRPC uses a variety of factors to assess basin condition:
• Impervious land cover — Roads, parking lots and other hard surfaces that prevent or limit water infiltration into the ground.
• Forest land cover — The amount of trees covering the land.
• Riparian land cover — The level of vegetation in the area directly adjacent to a river, lake, stream or other body of water.
Based on these factors, a basin can earn one of five categorizations. Basins identified as intact or sensitive have few impervious surfaces, are mostly forested and have healthy shorelines. Impacted basins show some effects from the development. Basins identified as degraded or very degraded are the most urbanized.
These categorizations correlate with the health of streams for fish and other aquatic species. Intact basins tend to have better water quality, while very degraded basins tend to have poor water quality.
In 2021, the condition of six basins improved. Four basins saw their condition upgraded from sensitive to intact, one upgraded from impacted to sensitive, and one upgraded from degraded to impacted.
Most of these improvements were in basins located in Capitol State Forest or in private timberlands. Cycles of replanting and regrowth contributed to the improvements in the condition of these basins.
No basins saw their assessed condition degrade. There were nine basins categorized as degraded or very degraded in 2021: eight are in the Lower Deschutes/Budd Inlet watershed and one is Woodland Creek in the Henderson Inlet watershed.
TRPC’s assessment also projected the future condition of Thurston County’s basins based on the amount of development anticipated by 2045. Over the next 20 years, countywide impervious land cover is expected to increase by less than 1 percentage point.
Based on current zoning and development regulations, the overall health of the county’s basins is expected to remain unchanged from 2021 conditions. Projections of future basin conditions don’t consider the potential for restoration and conservation efforts.
To view the full assessment, visit https://tinyurl.com/mwvbrpyh.
