WITHDRAWN - Investigating Uncertainty of Groundwater/Surface-water Interactions in the Lower San Antonio River Basin, Texas

The quantification of model uncertainty provides important information regarding a model’s ability to predict a quantity of interest. Linear-based First-Order Second-Moment (FOSM) analysis is a technique that yields initial estimates of model predictive ability, also referred to as model reliability. In this study, a novel groundwater/surface-water model of the lower San Antonio River basin and surrounding areas is in development and is being paired with FOSM analysis to quantify the uncertainty surrounding simulated groundwater/surface-water exchange. In light of recent drought conditions, a predictive drought scenario of streamflow response to reduced rainfall and increased groundwater withdrawals will be investigated. The study’s main goal is to develop a tool that can assess spatial and temporal variations in flow occurring between the lower San Antonio River (and its major tributaries) and underlying aquifer units these streams traverse during 2006 through 2013. The modeling analysis may indicate reaches with potential for streamflow depletion within the basin. FOSM analysis is being applied through the use of PEST++ and pyEMU. Observations include groundwater levels within the Texas coastal uplands and Texas coastal lowlands aquifer systems and groundwater contributions to base flow in main-stream reaches. The results of this analysis will include simulated volumetric surface-water totals with associated uncertainty at the confluence of the San Antonio and Guadalupe rivers, which will provide improved understanding of how streamflow is affected by groundwater pumping within the basin.