In the State of Our Watersheds report the Nisqually Indian Tribe points to increases in impervious surface and the impact it could have on salmon. The animations below show the shift in paved land in 1986, 2006 and (estimated) 2026.
As the population continues to increase, so will the impervious surface area, causing a disruption of both the ground and surface water ecology. This disruption will negatively impact the ecosystems dependent upon the proper function of the hydrologic cycle. “Tributary watersheds important for chinook (Mashel and Ohop) are mostly managed for forest products in the upper portions of their drainage areas. Our analysis identified a concern that, in the future, portions of these watersheds may convert to a higher percentage of urban or rural-residential use” (Nisqually Chinook Recovery Plan, 2001).
Impervious surface causes increases in stream temperatures, decreases in stream biodiversity, as evidenced by reduced numbers of insect and fish species, and contributes to pollutants in stormwater runoff, which can contaminate local aquatic systems (Schueler, 2003). Currently, the Nisqually watershed is in relatively good condition, but there is a trend as population continues to grow within the watershed that the impervious surface will likewise increase. Without proper management and resource protection the forecast is for impervious surfaces to have grown to an “impacting” level within 15 years.