Eulerian-Lagrangian approach time steps

At every time step, MODFLOW already calculates the directional components of specific discharge Qx 9y lx across every cell s six faces (See equation (4)). Subscripts x, y, and z indicate mutually orthogonal Cartesian coordinates, which are specified at t = 0 whether one chooses a Lagrangian or an Eulerian approach. These components of specific discharge q can be retrieved from within the current calculations of MODFLOW. This means that one of the three vectors that appear in equation (12) is already available. One more of the three flow vectors is required in order for all three to become known. 

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