Development of a model for simulation of solute transport in a stream aquifer system

Abstract

A model for simulation of solute transport in a stream-aquifer system is developed. The model is referred to as: Model for Stream-Aquifer Solute Transport or MSAST. The MSAST is developed by coupling four primary models: The groundwater flow model, MODFLOW-96, the coupled groundwater surface water model, MODBRANCH 3.7, the aquifer solute transport model, MT3D 1.11, and a fourth model developed in this study referred to as Stream Solute Transport Model or SSTM 1.0. The flow interaction in a stream-aquifer system is simulated by the MSAST using MODFLOW and MODBRANCH. The solute interaction in a stream-aquifer system is simulated by the MSAST using MT3D and SSTM. An interface is developed between MODFLOW-MODBRANCH and MT3D-SSTM. SSTMLINK Package is added to MODBRANCH to create an interface file containing streamflow hydraulic solution for the stream network. The LKM Package (Zheng, 1990) creates an interface file that contains the output solution of MODFLOW. The SSTMLINK and the LKM Packages interface files are used as input files in the MT3D-SSTM simulation. The Stream Solute Package (SSL1) is added to MT3D to simulate variable stream concentration by calling the SSTM. The SSTM is coded based on the one-dimensional advection dispersion equation. The finite difference method is the numerical technique implemented in the SSTM. MSAST is used to simulate chloride transport in the stream-aquifer system of the Arkansas River and the Equus Beds Aquifer in south-central Kansas. Previous modeling of the aquifer was conducted by the Bureau of Reclamation using MODFLOW and MT3D to examine groundwater flow and chloride transport in the aquifer. The flow interaction in the MSAST application was simulated using MODFLOW and MODBRANCH. The solute interaction was simulated using MT3D and SSTM. The SSTM requires initial and boundary solute data values. These data are not available in the range of time intervals used by SSTM. The mean concentration of chloride for several disperse measurements in time and space taken for the Arkansas River are used as the initial and boundary values. The simulated mean of chloride concentration in the river matched the observed mean. Chloride concentration in the aquifer decreases in the vicinity of simulated channel for the selected simulation time. Sensitivity analysis showed that the increase in river chloride concentration has a significant effect on chloride concentration in the aquifer.