COMPARISON OF CHLORIDE MASS BALANCE AND BASEFLOW INDEX APPROACHES TO RECHARGE ESTIMATION IN THE TEXAS GULF COAST AQUIFER, USA

The most widely used approaches for recharge estimation are the chloride mass balance (CMB) and baseflow index (BFI) because data for these methods are readily available. Here we compare the two approaches using the Texas Gulf Coast aquifer as a case study. Regional recharge was estimated using groundwater chloride analyses from 10,500 wells and streamflow hydrograph separation from 59 unregulated gages. CMB recharge rates range from <3 mm/yr in the south to 250 mm/yr in the north, correlated with increasing precipitation (650 – 1370 mm/yr). Unsaturated zone chloride profiles show large local variability related to soil texture and vegetation. Recharge estimates based on BFI analysis also increased from south to north (0.5 – 180 mm/yr), and are highly correlated with CMB estimates (r = 0.70). The general consistency in spatial recharge trends and rates shows promise for widespread application of CMB and BFI techniques for recharge estimation.