Northrop Consultants have been commissioned by West Coast Developments on a brief prepared by Wollondilly Shire Council to examine the flooding hazard of the Cawdor Urban Release Area. This study was required to assess the effect of the proposed urbanisation of the Study Area on the flood discharges and levels.

The study area covers approximately 550Ha and has a catchment of approximately 30 km2, which discharges into the Nepean River, via the Matahill Creek. This study has identified approximately 148Ha as being subject to flooding for a 1% AEP. Details of the study area are shown in Appendix A.

The principal objectives of the study were:

• estimate the flows in floods of differing probabilities of occurrence
• using the flows derived to estimate the flood levels and velocities for floods of differing probabilities
• investigate retention structures to limit the developed discharges to less than the undeveloped discharges
• investigate design of channelisation to contain low recurrence interval runoff which would otherwise cause nuisance flooding to recreational areas
• satisfy the council's brief relating to flooding of the proposed development, and surrounding areas.