Climate Variability and Irrigation Impacts on Stream-Aquifer Dynamics in the Apalachicola-Chattahoochee-Flint River Basin

Abstract

Climate variability cycles are responsible for short term fluctuations in climatic conditions thereby, affecting the water cycle and the availability of freshwater resources around the world. In Southeast United States, climate variability induced droughts have been a major factor affecting the availability of freshwater resources that threaten endangered mussel species in the Flint River and shellfish industry in the Apalachicola Bay. Recurring droughts have also led to the Tri-State Water Wars in this region. One of the primary issues related to the conflict is the reduction in baseflow levels in the Flint River during droughts due to irrigation withdrawal from the Upper Floridan Aquifer (UFA). Therefore, this research was conducted to study the compounding effect of climate variability induced drought and anthropogenic activities, such as, irrigation water withdrawal on baseflow levels in Apalachicola-Chattahoochee-Flint (ACF) River basin. The non-parametric Joint Rank Fit (JRFit) procedure and MODular Finite-Element Model (MODFE) were used to study and understand the relationships among droughts, irrigation, and stream-aquifer interactions in the study area with the final goal of identifying critical reaches and tributaries of the lower Flint River that are largely responsible for lowering of flow levels in the river. Results indicate that baseflows exhibits El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and North Atlantic Oscillation (NAO) tele-connection in this region. Interaction tests showed that La Niña is modulated by the phases of PDO and AMO. The results of this study also suggest that streamflow levels have decreased significantly after the introduction of irrigation in the study area. Results suggest that lowering of flow levels mainly occurs during La Niña phases and gets exacerbated during growing periods. Analysis of presumptive standard flow showed that flow levels repeatedly violated the standards in recent drought events and can result in impairment of aquatic ecosystems. The results from the MODFE model indicated that increased ground-water withdrawal resulted in decrease in the stream-aquifer flux in the study area. The results from sensitivity analysis and simulated water restrictions suggested that acreage buyout in the sensitive areas help in greater recovery of stream-aquifer flux than, that achieved by reducing irrigation intensity (15% or 30%) throughout the study area. Moreover, analysis of acreage buyout suggested that water restrictions on irrigation withdrawal can have significant impacts on stream-aquifer flux in the study area, especially in the critical watersheds such as Spring Creek and Ichawaynochaway Creek. The results of study are helpful in better understanding of the combined impact of climate induced droughts and anthropogenic stresses on stream-aquifer dynamics of Flint River and might help the state of Georgia to formulate an alternative drought-water use policy that can address the current water scarcity condition. Additionally, the results from this study can help better manage groundwater resources, protect surface water flows, and help avoid irrigation induced streamflow depletion in some of the most vulnerable tributaries of the Flint River.