Lake Macquarie City Council & Sea Level Rise

In Lake Macquarie City Council:

The required minimum floor level is based on:
1. planning for a 1:100 year flood of 1.5mAHD (Australian Height Datum - average sea level in 1971)
2. plus 0.49m for sea level rise by 2050 (denied by LMCC general manager to Garry Edwards)
3. plus a freeboard (0.37m).

1. The highest recorded flood was to 1.25AHD in 1949 in one place where the water banked up. More recent levels were 1.05AHD in 2007 and 1.0mAHD in1990. The lake level ranges from 0.1 to 0.4m AHD.
In addition the modelled 1% Average Exceedance Probability (AEP) flood level for the lake is 1.38m AHD (not 1.5mAHD!)

2. An 0.49 m rise in 50 years would be nearly 10mm per (1cm) per year in sea rise The historic sea level rise averaged for all data collected for this part of coast (both Fort Dennison and Newcastle) is a tiny 0.9mm/year. Source: NTC 2007

(http://soer.justice.tas.gov.au/2009/indicator/21/index.php)

The latest accurate data shows our part of the coast (from Port Kembla) having averaged a relative rise (which is as experienced) from July 1991 to June 2011 of 2.6mm/yr with a change of net relative trend of +0.5mm from June 2010-June 2011.
(http://www.bom.gov.au/ntc/IDO60202/IDO60202.2011.pdf)

This graph is of past and predicted average sea rise is from the IPCC 2007 report.

Figure is at http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-5-1.html

3. LMCC have adopted 'freeboard' from the former NSW Government’s Flood Risk Management Guide

Incorporating sea level rise benchmarks in flood risk assessments.
“The typical 0.5 metre freeboard outlined in the NSW Floodplain Development Manual (NSW Government 2005) for general residential development provides a factor of safety to ensure that the risk exposure selected is accommodated. This freeboard includes a component related to climate change impacts on flood levels in coastal and non-coastal areas and a wide variation in sensitivity of estimated flood levels to flood flow. The freeboard provides a relatively small allowance to accommodate some of the projected increases in rainfall intensity from flood-producing storm events associated with climate change."

In a flat area with no mountains it requires an increase of 370mm of rain in one event! This is not a 1 in 100 year 'design' event, but truly Epic.

Consequences:
Putting the design floor level so high is affecting thousands of households and business, reducing access to the water front, reducing accessibility as it rules out disabled ramping and older people living in many areas of the city. Worse the "fear" is driving action in labelling property as at risk (which has never been flooded) and increasing insurance for no good reason.

It has also made my job as an architect hard as it reduces good and equitable solutions in these areas and results in poor connectivity to the street.

Since 1990 we have now over 20 years of quality data, and as a theory 'Global warming' has some issues. The correlation between warming and Carbon Dioxide levels has not been been proven (some data in 'climategate' was revealed as tweaked to achieve better correlation). I wish all may read the IPCC reports, with the caveats and issues, not just the bits for politicians.

For a more detailed report see: LakeMacquarieMinimumFloorLevelSeaLevel.pdf