Wave Energy Converters (WECs) inherently extract energy from incident waves. For wave energy to become commercially viable, large wave farms of WECs will be required. This amount of energy extraction will increase the potential for changes in the local wave field and coastal environment. Assessments of these effects are necessary to allow WEC developers to complete Environmental Impact Assessments (EIAs) prior to deployment. This quantification faces several difficulties forcing developers to rely on techniques like ongoing monitoring of small scale test sites and hydrodynamic modelling. This paper focuses on improving the representation of the wave farm within a spectral wave model. To increase the reliability of a numerical model it is of paramount importance that the wave farm is as represented as close to reality as reasonably possible. In early development WEC arrays were represented as either a single obstacle or as individual devices with a constant transmission coefficient. Constant transmission and reflection coefficients are unrealistic as the devices display frequency-dependent energy absorption characteristics that will correspond to the spectral response of the WEC. Post processing of data collected during physical experiments of a wave farm of Oscillating Water Columns (OWCs) has provided frequency dependent transmission and reflection coefficients. Several test cases were created using MIKE 21 Spectral Wave Model developed by DHI Water and Environment. The results demonstrate the shortfall of these early techniques particularly the overestimation of the impact within the transmission zone. It is evident that it is essential to account for wave energy extraction and radiation within the transmission and reflection coefficients applied to individual WECs within an array.