Investigating drivers of groundwater-surface water interaction in the lower Flint River Basin, southwestern Georgia, USA
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Groundwater provides the majority of global water resources for domestic, agricultural, and power use while contributing surface baseflows to support healthy aquatic ecosystems. Understanding the extent and magnitude of hydrologic connectivity between groundwater and surface water components in karst watersheds is essential to the prudent management of these hydraulically-interactive systems. The objective of this research was to examine groundwater and surface water connectivity between the Upper Floridan Aquifer (UFA) and streams in the Lower Flint River Basin (LFRB) where development of agricultural irrigation intensified over the past 30 years. An analysis of USGS streamflow data for the pre- and post-irrigation period showed summer baseflows in Ichawaynochaway and Spring Creek were reduced by an order of magnitude in the post-irrigation period, indicating the strong hydraulic connection between these streams and the underlying aquifer. These data also revealed steeper annual and seasonal baseflow recession occurring within Ichawaynochaway Creek associated with periods of intensive regional groundwater pumping rather than climatic patterns. Between 2010 and 2011 physiochemical monitoring on 50 km of Ichawaynochaway Creek confirmed close hydraulic associations between this stream and the UFA. Specific conductivity was highly correlated with Ca2+ and indicated as much as 42% of groundwater consistently entered through five out of the 50 reaches sampled. Stable isotope values (δ18O and δD) detected rapid turnovers in the quality and source of baseflow between sampling events and no significant connection between the UFA and depressional wetlands or the surficial aquifer in the study area. Finally, a large scale comparison performed to detect patterns in geomorphology at the surface, near surface and sub-surface levels, indicated a basin-wide NNW trend was shared in stream reach direction, bedrock joint azimuths and orientation of conduits in regional phreatic caves which is in agreement with tectonic fracturing. The dominant N-S trend in stream reach direction suggested regional fluvialgeomorphology is significantly influenced by neo-tectonic patterns, but partially adjusted to the tectonic template; therefore, investigating intersecting templates may warrant further investigation. The results of these hydrologic, physiochemical, and geomorphic studies provide data which are immediately useful for informing basin models and methods which are easily transferrable to other basins.