Here upore is the pore velocity. Instead using the Darcy velocity u=upore/εp, multiplying the equation with the porosity εp, and rescaling γ such that it again can be set proportional to the maximum magnitude of the velocity field u, the equation can be rewritten as:

To obtain exact numerical conservation of the integral of εpϕ, switch to the conservative form

The conservative form can be derived from the nonconservative form if it is assumed that the velocity field u satisfies the following continuity equation: