Avoca Lagoon Floodplain Management Study

Avoca Lagoon is the largest of the four coastal lagoons within Gosford. The lagoon has a cruciform shape with a surface area of 97.5 hectares and average depth of 1.3 metres. The let-out-level is approximately 2 metres above mean sea level. The lagoon entrance is normally closed due to the action of coastal dynamic processes which result in the formation of a beach berm across the lagoon entrance, linking Avoca and North Avoca beaches. Gosford City Council has records of openings of the Avoca Lagoon entrance commencing in 1972. These records show that the entrance has been opened 58 times over the period 1976 to 2003, primarily for flood control purposes. The entrance has broken out naturally on four other occasions when floodwaters caused the lagoon level to rise above the level of the beach berm. Records of inundation of Avoca Lagoon by ocean storms are not as complete as those available for the opening of the entrance. Limited data are available for severe ocean storms in May 1974, June 1978 and August 1986 when waves overtopped the beach berm and entered the lagoon.

The floodplain management process seeks to promote the adoption of an integrated approach to the management of all lands within the Avoca Lagoon catchment. This floodplain management study addresses the following issues:

• existing flood behaviour;
• environmental and planning considerations;
• future development;
• climatic change;
• flood damages;
• floodplain management options;
• floodplain management impacts;
• floodplain management economics;
• preferred floodplain management strategies.