Investigating the Impact of Extreme Events on Aquifer Levels and River Baseflows in the Suwannee River Basin, Florida.

In Florida, tropical systems and spring frontal storms can supply substantial and widespread rainfall that can significantly recharge the Upper Floridan Aquifer (UFA). Due to the karstic properties of the UFA, recharge can be rapid and extensive, drastically changing aquifer levels over short timescales. Changes in groundwater levels also have profound effects on hydraulically connected surface waters, as many rivers that flow through the unconfined UFA are primarily sustained by groundwater. The UFA is a highly utilized aquifer, supporting most of the potable water supply and a thriving yet ever-growing agricultural industry. Therefore, understanding causes of UFA groundwater level variability and recharge dynamics has become an important water management concern. However, quantifying the unique impact extreme events can have on aquifer levels has been limited in scope. By investigating the effects that extreme events, such as tropical systems, have on short and long-term groundwater levels in the UFA and focusing our analysis along the middle Suwannee River Basin in northern Florida we gain insight into the impact of extreme events on recharge dynamics. The middle Suwannee River reaches are primarily sustained through several major springs and thus changes to UFA groundwater significantly impact riverine and spring ecosystems along this river corridor. We use time series analysis and frequency statistics to analyze recharge dynamics and long-term persistence after significant storm events which are then compared to aquifer responses generated by seasonal weather patterns and long-term climate oscillations. Following tropical storm Debby in 2012, a change point analysis detected a persistent, regional change in mean groundwater level at multiple wells in the UFA. However, the significantly elevated groundwater levels did not coincide with any long-term detectable change in precipitation. These preliminary analyses suggest that the impacts of a single event on groundwater levels may be more significant than seasonal rainfall. We expand our analyses to other tropical systems and concurrently assess the impact they have on baseflow to the middle Suwannee River.