Estimation of lateral water flow and bromide transport in a subsurface seepage irrigation system

Subsurface seepage irrigation is a common method used by growers in the Tri-County Agricultural Area (TCAA), Florida, USA, owing to its cost-effectiveness and low maintenance requirements. This study investigated the lateral flow of the perched water and the lateral transport of bromide (Br⁻) in this irrigation system in the TCAA and estimated the potential discharge of Br⁻ into the drainage canals at the edges of the field, using the Visual MODFLOW/ MT3DMS models in conjunction with field experiments. Simulations showed that the perched water flowed from the northeast to the southwest of the field. Migration of the Br⁻ plume from the source areas toward the canals was very slow and varied depending on the selection of the outer Br⁻ concentration contour levels. However, the lateral transport of Br⁻ from the perched water into the canals occurred after about 61 days. The simulations further revealed that the rate of perched water Br⁻ discharge into the canals averaged 8.6 g day⁻¹ during a 30-day discharge period (from 61 to 91 days). This rate is very important for estimating Br⁻ discharge into the canals and could also provide useful information for evaluating dissolved nutrient discharge into canals from the subsurface seepage irrigation system.