Effect of elevation resolution on evapotranspiration simulations using MODFLOW
The regional groundwater flow model of the Rincon Valley-Mesilla Basin area (NMOSE-2007 flow model) is revised in this work for use with the water managers of the region. A Groundwater Vistas (GV) based numerical model is developed to analyze the simulation results. Layer elevations derived from the revised hydrogeologic cross sections for the Mesilla Basin are incorporated. Model performance is improved by minimizing the uncertainty in input parameters specific to mountain front recharge and boundary flows.
Effect of model grid size to simulate the evapotranspiration (ET) component of groundwater is investigated in the present research. Source code of the evapotranspiration package (EVT) in MODFLOW is modified by solving the groundwater flow equation at the user specified digital elevation model (DEM) resolution. Uncertainty in groundwater depth at DEM resolution is eliminated by characterizing the variability in both land surface and piezometric elevations. An area of interest delineated by the boundaries of model grid cells is specified to minimize the runtime. A new option to approximate the ET represented area by the boundaries of the DEM cells is introduced to improve the model performance.
Applicability of the present research is evaluated on the modified NMOSE-2007 flow model. The 10 m DEM of the study area is aggregated to various coarse resolution grids that are integer multiples of model grid resolution. Model sensitivity to variability in elevation input data is investigated at different resolutions. Results of the analysis conclude that both cumulative ET outflows and ET rates from the model are decreasing towards coarse resolution grids. An optimum grid resolution by striking the balance between computational run time and model prediction accuracy is suggested for use with the head dependent packages. Statistical analysis on the estimated parameters conclude that simulating the ET component of groundwater at 80.487 m resolution and aggregating the ET outflows to model cell resolution would improve the performance of the model.
0543: Civil engineering