New MOC Model of Seawater Transport in Coastal Aquifers

A new miscible seawater transport model, based on a variant form of the traditional method of characteristics (MOC), is presented. The distinctive features of this model are moving packets with preassigned volumes instead of concentration, numerical tracking of moving packets using fourth-order Runge-Kutta method, and direct computation of total transport due to advection and hydrodynamic dispersion. In addition to quantification of seawater circulation, the model output illustrates (1) the path followed by seawater inside the aquifer; (2) the buildup of seawater storage; and (3) the position and advance/retreat of a disperse interface. The model has been assessed using two benchmark test problems and subsequently applied to the Biscayne aquifer in Florida. All model runs were characterized by low mass balance errors (<0.2%).