Traditional elliptic harbor wave models are based on the assumptions that the region outside the computational grid is of constant depth and that the exterior coastlines are collinear and fully reflecting. These assumptions, which are associated with the open boundary, are generally not met in practice. This paper demonstrates that the effects of exterior depth variations on model results can be substantial, leading to unreliable simulations even with sophisticated modern wave models. A technique is developed to overcome these limitations. It is based on a one-dimensional representation to better simulate the effects of the exterior bathymetry. The results of the one-dimensional model are then interfaced along the open boundary of a two-dimensional finite-element harbor wave model. The new model is tested against analytical solutions for the case of wave propagation on a sloping beach, which is a difficult problem for harbor models in use today. Excellent results are obtained, suggesting that improved representation of the cross-shore slopes while treating the open boundaries may enhance the usefulness of these models.