A concrete arch dam have been analyzed during seismic loading with a model based on acoustic elements to describe the water and infinite elements as quiet boundaries to prevent wave reflection. The results have also been compared with a simplified model based on Westergaards added mass approach. The simplified model is only used, in this study, for comparison with the more advanced model with acoustic elements. Therefore the results from this simplified model are just used as a rough estimate of the induced stresses and displacements. Despite this, the simplified Westergaard model gives similar results compared to the more advanced model with acoustic elements for the water and infinite elements for the boundaries. The largest difference between the models often occurs at the nodes in the base of the arch dam, which may be due to poor discretization. Generally, the Westergaard added mass gives higher maximum principal stresses at the base on the upstream side than the acoustic model, while often underestimating the min principal stresses at the base on the downstream side. Both models show high tensile stresses near the base of the arch dam that would result in cracks.