Portions of the Port Stephens Local Government Area (LGA) is affected by flooding. This is due to the presence of major river systems in the western regions of Port Stephens and the low lying topography as well as interactions with the coast and estuaries in the east.
Flooding in the LGA is caused by:
- river or creek banks being overtopped;
- estuary levels rise and cover foreshore areas; and
- stormwater drainage that is unable to cope causing overland flows (down streets or across other urban areas).
Council manages land affected by flooding by:
- undertaking studies that identify flood risk and flood levels;
- undertaking floodplain risk management studies and plans that provide provisions for the management of flood prone land; and
- assessing the compatibility of new development (and major renovations) with flood risk thereby encouraging development that is appropriate to the flood risk of the area.
Common Flood Definitions
The chance of a flood of a given or larger size occurring in any one year, usually expressed as a percentage. Eg, if a peak flood discharge of 500 m3/s has an AEP of 5% it means that there is a 5% chance (that’s is one in 20 chance) of a 500m3/s or larger events occurring in any one year.
Provides reasonable certainty that the risk exposure selected in deciding on a particular flood chosen as the basis for the FPL is actually provided. It is a factor of safety typically used in relation to setting of floor levels. Freeboard is included in the flood planning level.
Relatively high streamflow which overtops the natural or artificial banks in any part of a stream, river, estuary, lake or dam, and/or local overland flooding associated with major drainage before entering a watercourse and/or coastal inundation resulting from suer-elevated sea levels and/or waves overtopping coastline defences excluding tsunami.
Land that is likely to be inundated by the probable maximum flood (PMF is the largest flood that could conceivably occur in a particular catchment) and defines the "floodplain" for that catchment.
The level of the 1% AEP (annual exceedance probability) flood event in the year 2100 plus 0.5 metre freeboard.
The area of land below the FPL and thus subject to flood related development controls.
Land that is a pathway taken by major discharges of floodwaters, the partial obstruction of which would cause a significant redistribution of floodwaters, or a significant increase in flood levels. Floodways are often aligned with natural channels, are usually characterised by deep and relatively fast flowing water, and have major damage potential.
Those parts of the floodplain that are important for the temporary storage of flood waters. The loss of storage areas may increase the severity of flood impacts by reducing natural flood attenuation.
The remaining area of flood prone land after the Floodway area and Flood Storage area have been defined.
The area of flood which poses a possible danger to personal safety, where the evacuation of trucks would be difficult, where able-bodied adults would have difficulty wading to safety or where there is a potential for significant damage to buildings.
The area of flood where, should it be necessary, a truck could evacuate people and their possessions or an able-bodied adult would have little difficulty in wading to safety.