GROUNDWATER EXTREMES AND ROBUST STREAMFLOW DISTRIBUTIONS IN THE SOUTH PUGET SOUND: A HYDROLOGIC ANALYSIS OF WATER YEARS 2008 THRU 2012

Annual stream discharges in Thurston County, Washington have doubled to tripled due to persistent La Nina patterns (> 50 inches of rainfall) in the last 5 years. Hydrologic monitoring stations for the 750 square mile region show that the broad distribution of rainfall each water year has created robust and varied flows including higher summer low flows (great for fish habitat) and increased discharges to marine waters. While extreme daily rain events have not developed in the last three years (unlike the previous decade from 1999-2009) steady inputs through late spring have created high ground water and problematic lake levels. Larger rivers have also followed suite: the Deschutes, Nisqually and Chehalis were above the 95% percentile through mid-August of 2012 for the 38 to 82-year records. Consequences of high ground water recharge have also been lake algal blooms, new emergent nitrate hot spots and record numbers of slope failures. Land use policy implications are numerous with a greater need to understand and prioritize hydrologic data collection, analysis and numerical modeling efforts. Understanding sea-level rise coupled with new terrestrial discharge findings will be paramount to South Puget Sound planning.