MODELING MACROPORE TRANSPORT OF AGRICULTURAL CHEMICALS ON A RIVER FLOODPLAIN: MODEL FORMULATION

摘要

Modeling methods were developed to simulate groundwater flow and atrazine transport at a research site on the Brazos River floodplain. Conceptualized macropores were utilized to simulate preferential flow through a highly structured clay soil. The United States Geological Survey (USGS) model, Variably Saturated Two Dimensional Transport (VS2DT), was used to simulate macropore transport of agricultural chemicals through the soil to a sand and gravel aquifer. The clay soil flow domain was decoupled from the sand and gravel aquifer. Transport simulation in the aquifer used inputs from the simulation of transport through the clay soil. The model simulated variably saturated flow in the macropores, clay soil matrix and floodplain aquifer using the Richards equation and chemical transport using the advection-dispersion equation. The flow domains for the clay soil and aquifer were detailed. Model inputs for groundwater flow and atrazine transport and the associated boundary conditions are presented.