Different effective boundary conditions or wall laws for unsteady incompressible Navier-Stokes equations over rough
domains are derived in the laminar setting. First and second order unsteady wall laws are proposed using two scale asymptotic
expansion techniques. The roughness elements are supposed to be periodic and the influence of the
rough boundary is incorporated through constitutive constants. These constants are obtained by solving steady
Stokes problems and so they are calculated only once. Numerical tests are
presented to validate and compare the proposed boundary conditions.