Effects of irrigation withdrawals on streamflows in a karst environment: lower Flint River Basin, Georgia, USA

Extensive implementation of centre pivot irrigation systems occurred between 1970 and 1980 in the lower Flint River Basin (FRB) of southwestern Georgia, USA. Groundwater within this karstic system is in direct hydraulic connection with regional streams, many of which are incised through the overburden into underlying limestone. We used long‐term U.S. Geological Survey gaging station data to evaluate multiple flow metrics of two tributaries (Ichawaynochaway Creek and Spring Creek) in the lower FRB to determine the extent of changes in stream behaviour since irrigation practices intensified. We compared pre‐ and post‐irrigation flow duration curves, 1‐, 7‐, and 14‐day minimum flows, and 8‐day (seasonal) and annual baseflow recession slopes, in addition to evaluating regional climate data to determine whether significant differences existed between the pre‐ and post‐irrigation periods. Our results showed significant changes in low‐flow durations in the post‐irrigation record for both gages, including a decrease by an order of magnitude for 98% exceedance flows at Spring Creek. Both gages indicated significant reductions in 1‐, 7‐, and 14‐day low flows. Eight‐day baseflow recession curves (within early summer months) and annual baseflow recession curves became significantly steeper during the post‐irrigation period for Ichawaynochaway Creek. We also found that a significant relationship existed between winter and summer minimum flows in both streams in the pre‐irrigation period which was disrupted in post‐irrigation years. Regional climate data for the study period revealed no significant changes in rainfall totals or frequency of drought; however, there was evidence for a shift in seasonal rainfall patterns. Copyright © 2011 John Wiley & Sons, Ltd.