Cut in levee could result in bad flood

SHOALHAVEN City Council has deferred consideration of a report on the risks of flooding in historic Terara so councillors can visit the area to gain more information.

The low-lying village on the southern bank of the Shoalhaven River was wiped out by two devastating floods in the mid and late 1800s; the second so bad many residents packed up what was left of their possessions and moved to Nowra.

Following another flood in August 1974 the Terara levee was built, predominantly on private land, to protect the village from direct inundation from the Shoalhaven River in a one-in-10-years flood. 

The levee originally comprised a raised mound, generally between 0.5m to 2m in height, and while not designed as a ring levee to provide full protection of the village, its purpose was to deflect the floodwaters from the Shoalhaven River. 

In 2006, following the recommendation of a geotechnical assessment, council reconstructed and raised the levee to cater for a one-in-20-years flood.

A report to the Policy and Resources Committee by Planning and Development Services director Tim Fletcher revealed one landowner had removed a section of the levee on private property, which could result in increased flood depths, velocities and flows to surrounding properties and public roads. 

The report said the landowner removed a 20m wide by 0.7m high portion of the levee, making it lower than its original level prior to the upgrade works. 

The owner informed council that in times of flood they would manually place an un-engineered temporary structure from galvanised posts and corrugated iron, in this lower section. 

The report said without engineering certification it was unlikely the structure would withstand the expected flood forces and could become hazardous debris in floodwaters. 

Council said if the landowner was unable to install the structure it could result in increased flood depths, velocities and flows to surrounding properties and public roads. 

Parts of the village could experience flood velocities and depths worse than before the 2006 upgrade. 

During the recent June 2013 Shoalhaven river flood, the structure was not installed because the landowner thought no overtopping was predicted.

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