The Shoalhaven Local Government Area (LGA) manages 11 of the State’s 102 ICOLLs. The natural opening and closing of ICOLLs occurs on an irregular basis. A number of factors contribute to entrance conditions. Generally entrance closure is initially triggered by waves from a severe ocean storm washing sand from the entrance spit into the channel, thereby restricting tidal flow through the entrance. Reduced seaward flow over a period of time leads to the channel gradually shoaling completely until the point of closure. A series of ocean storms can hasten shoaling. Following closure the entrance may open naturally from a flood which scours a channel through the spit and the typical tidal regime resumes. A large flood is required to establish the substantial channel that is required to ensure a viable long-term open entrance.
Due to increased development in low lying areas, as well as their tourist values, the Shoalhaven ICOLLs have been under increased pressure. Council in partnership with state agencies and its community has developed Entrance Management Plans (EMP). At the time of developing the plans, limited flood information was available. Therefore the plans were driven by water quality concerns and low level nuisance flooding. Floodplain Risk Management Studies and Plans are being prepared for these catchments. These will identify and evaluate potential entrance management options, using various modelled entrance scenarios in present and future climate conditions. In addition to catchment derived flooding, ocean derived flooding are also being modelled. Preliminary modelled results clearly challenge current entrance management practices and community perception of flood risk by showing that an open entrance could pose a greater flood risk to the community than a closed entrance under certain flood conditions. The feasibility of permanent flood mitigation and entrance management options such as engineered options or strategic planning in light of current climate change predictions are investigated in developing the Floodplain Risk Management Plans.