In this study regular and irregular waves are simulated with a numerical model. The aim of this study is to perform a numerical investigation into the reflection and transmission of the different waves forcing in a porous breakwaters. There are different types of numerical models available for solving the behaviour of waves in coastal regions and harbours. The most known numerical models are Boussinesq type wave models and non-hydrostatic wave models. In this study, the non-hydrostatic approach is chosen. Last years developments shows that this approach is competitive to Boussinesq type wave models in terms of robustness and the computational resource required to attain reliable outcomes in challenging wave and flow conditions. The simulations are performed with the non-hydrostatic model called SWASH, because it is a model that still is in development a validation of the model with this study is beneficial for the development. The influence of wave conditions and breakwater characterises on the reflection and transmissions are examined. In a number of cases the influence of the porosity, wave height, wave period and the width of the breakwater on reflection are investigated. The model predictions are found to be consistent with lab experiment, analytical solutions and empirical formulations. The reflection and transmission of bound long waves were also studied. The influence of the relative depth (kh) on the reflection and transmission was investigated. The model predications on the reflection of the bound long waves are found to be consistent with lab experiment. The model prediction deviates not more than 15 percent of the experimental results. On the other hand, the transmission of short waves and bound long waves were inconsistent with lab experiment. The most likely explanation for this inconsistency is the large deviation between the breakwater geometry used in SWASH and the experiment. In SWASH it is not possible to vary the porosity in vertical direction, so it was necessary to schematize the breakwater since the used breakwater in the experiment composed of two different porosities.