Two flood studies of major catchments within the subsidence area have been prepared for the Project – the Yarramalong and Dooralong Valleys Flood Study, and the Hue Hue Creek Flood Study.

The studies have shown that both Yarramalong and Dooralong Valleys are significantly flood prone. The floodplain is subject to regular inundation. This causes bridges and culverts to be cut-off for long periods. Large sections of the main roads into both valleys are flood affected and many of the access roads pass through a floodplain.

The Hue Hue Creek floodplain flood depths are significantly less. The majority of this flood prone land is located in rural or public open space areas of the catchment rather than in rural residential area.

The flood study has undertaken an assessment of subsidence impacts on the flooding regime and flood liable structures. The EA has established comprehensive environmental safeguards to manage:

• Flood affected dwellings and structures;
• Flood liability;
• Flood hazard assessment;
• Property access;
• Time of ponding; and
• Proposed flood mitigation measures.

The Panel acknowledges that flooding already occurs on a regular basis in the Wyong LGA, including the Yarramalong and Dooralong Valleys, and that to avoid any adverse consequence of ponding from mining-induced subsidence, effective mitigation and remediation measures (e.g. improved drainage) should be planned and implemented. In its forthcoming Environmental Assessment report, W2CP will outline the likely impacts from subsidence and ponding as well as relevant mitigation and remediation plans.