ANSWERING LINGERING NITRATE TRANSPORT QUESTIONS USING A TOPOGRAPHICALLY-BASED, AND GIS-DRIVEN WATER TABLE MODEL

Excess nutrients and soluble agrochemicals are slowly transported along longer groundwater flow pathways, and due to the timescale of the transport, concentrations of these chemicals in stream water exhibit long time lags relative to surface application. Decision makers trying to address these groundwater to surface water pollution problems are often incumbered by the number of resources and specific expertise needed to run the sophisticated groundwater models used to estimate groundwater flow and solute transport. Development and testing of a simple GIS-based water table model would allow resource managers without that extensive background in hydrology or modeling estimate water table positions, flow directions, and transit times and to better understand groundwater hydrology in a watershed. This simplified water table model will have use in answering questions related to groundwater travel times, solute transport, and downstream water quality. Our objectives in this research are to: 1) Create, calibrate, and validate the performance a steady-state, GIS-based groundwater model that can be used to estimate water table position and groundwater transit times based on Dupuit's equation for flow in a phreatic aquifer; 2) Apply the model to estimate water table position, groundwater transit times, and watershed storage at the research catchments within the Savannah River Site, with a focus on answering persisting questions of related to the leaching of nitrogen fertilizer at the site following a clearcut and intensive management period focused on short-rotation woody crop production.; 3) Run a well-accepted groundwater flow model, MODFLOW, at the research catchments and compare the differences produced between this traditional model and the simplified Dupuit model; 4) Constrain estimates of subsurface water storage and explore watershed storage - discharge relationships that exist to evaluate the thresholds that govern the sequential release of water (and the solutes it carries).