This thesis analyses the flow over a surface mounted fence (SMF) with two different inlet conditions. The fence causes a large modification of the inlet flow. Two different types of instabilities affect this flow geometry: the Kelvin-Helmholtz instability in the separated shear layer and a 'shedding-type' instability which affects the entire recirculation region. In this study, two δ/h ratios are investigated while maintaining the same Reynolds number. It was hypothesized that the δ/h ratio affects the frequency of the K-H instability and subsequently the 'shedding-type' insatiability. Time-averaged flow fields were compared between the two cases. In an unsteady analysis, the Strouhal number of the dominant frequency of the K-H instability was investigated. The Strouhal number varied between the two due to velocity gradient at the separation point. The 'shedding-type' instability was also investigated and was found to be intermittent.