The solution of the mass balance equation for sedimentation and consolidation in sediment suspensions requires closure equations for the parameters diffusivity, permeability and effective stress. Experimental data for non-cohesive and cohesive materials are discussed. New semi-empirical relations, which are a better approximation of reality, are proposed. The non-uniqueness for cohesive sediments is explained in terms of differences in aggregation history. The numerical implementation of the unifying theory for sedimentation and consolidation faces some serious problems. Particularly, the discontinuities require the addition of artificial diffusivity to create the necessary damping to avoid overshoot-induced oscillations. Improved stability is obtained using a special finite-element technique. The model is validated with several data sets and proves to predict the right behaviour and density profile evolution for both non-cohesive and cohesive sediments. The remaining differences between measured and comp...