Formulae to describe porous flow

This report, under the auspices of MAST coastal structures, is a contribution to project 1, wave action on and in coastal structures. Derives formulae that can be used to describe the motion of water in a porous and rubble-mound structure. Shows that the Forchheimer equation can be derived using the Navier-Stokes equation. The required averaging of terms demands some simplifications. Discusses treatment of the friction terms, (laminar shear stresses and convective/turbulent shear stresses) and the added mass term. Uses an alternative approach based on the balance of forces, with consideration of laminar friction, drag resistance and added mass and derviations of expressions for the Forchheimer terms. Notes that measurements under stationary flow conditions cannot be used to derive values for some of the coefficients for non-stationary flow. (C.J.U.)