Coupled Mixing-Cell and Mass Balance Flow Path Models of the White River Flow System, Nevada, USA
AuthorSawyer, Frederick Emile
AdvisorThomas, James M
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ABSTRACT: Mass balance (MB), Discrete-State Compartment (DSC) (Campana, 1975) and Discrete-State Compartment-Shuffled Complex Evolution (DSC-SCE) (Carroll et al., 2007) models are compared for the White River Flow System (WRFS), in east-southeast Nevada, using δD and δ<super>18</super>O to evaluate 2006 recharge-discharge (RD) estimates and two water mixing scenarios in the WRFS. DSC models use a simple mixing-cell network for regional scale problems with limited data (Campana et al., 2001). DSC-SCE models combine the DSC and a global optimization algorithm, to obtain optimal solutions (Duan et al., 1992). The 2006 RD estimates and proposed flow paths are also evaluated using δD and δ18O values in a MB model. MB model results of calculated δD and δ18O values at regional springs are within ± 2 / and ± 0.2 / of observed values, respectively, expect for Pahranagat Valley. Thus, the MB model indicates that new RD estimates and resulting inter basin flow rates and proposed flow paths are reasonable for the WRFS. DSC models were unable to match 2006 RD estimates despite calibration with isotopes. Extremely large recharge and evapotranspiration (ET) values required to achieve calibration in some cells are improbable for the system and thus are not viable. However, these non-unique solutions and their results suggest that the system cannot be entirely explained by isotopes alone without any other constraints. DSC-SCE models provide additional flux and ET values based on the recharge estimates and isotopes; thus the DSC-SCE models may help constrain future water budget estimates. DSC-SCE results also suggest that the 2006 ET estimates are reasonable. MB, DSC and DSC-SCE model results imply that ET is most likely removed from local precipitation before any remaining precipitation mixes with regional groundwater in most valleys.