by Greg Martin

The NSW State Government has released its Environmental Impact Statement ( EIS ) on the proposal to raise the height of the Warragamba Dam wall and the report has been delivered to all interested parties .

The report gives an in-principle approval for the raising the dam height by 14 metres which would go a long way to preventing catastrophic inundations which cause loss of property and life in the Hawkesbury-Nepean Valley .

Submissions supporting or opposing the EIS are to be submitted by November 12 . One of the driving forces behind the raising of the dam wall is the Hawkesbury Nepean Flood Mitigation Action Committee ( HNFMAC ).

HNFMAC secretary , Maurie Smith , organised a meeting of members at Windsor RSL on October 18 and invited guests to discuss the EIS and formulate a response

“ All our members supported the EIS and voted unanimously to back the proposed raising of the dam wall which would go a long way to drastically reduce the damage caused by flooding downstream of Warragamba Dam ,’ Maurie said .

The group has lobbied hard for years in supporting the dam ’ s increase in heights .

The EIS ran to 46 pages but in summary , it highlighted the following reasons for increasing the dam height :

1 . The Hawkesbury-Nepean Valley has the highest single flood risk exposure in NSW .

2 . Raising Warragamba Dam would provide flood mitigation through the temporary storage and controlled release of floodwaters .

3 . Raising Warragamba Dam would reduce risk to life and reduce flood damages downstream by about 75 per cent on average .

4 . The Flood Strategy does not change the location of the existing floodplain development levels .

5 . Use of the dam for flood mitigation would not change the full supply level or lead to permanent upstream inundation .

6 . The proposed raising of Warragamba Dam is one of nine outcomes under the NSW Government ’ s Hawkesbury- Nepean Valley Flood Risk Management Strategy .

7 . Raising Warragamba Dam would reduce the flood risk but it will not completely eliminate all flooding impacts .

8 . Over 80 dams in Australia have been raised at some point after their original construction .

9 . Since records began in the 1790s , there have been about 130 moderate to major floods in the Nepean-Hawkesbury Valley . The largest flood in living memory was

in November 1961 , the year after the dam was completed , when the water reached 15 metres above normal river height at Windsor .

The Hawkesbury-Nepean Valley has a long history of flooding and according to the Insurance Council of Australia , the region has the highest flood risk exposure in the state and probably Australia .

In 2012 , extensive flooding across south-eastern Australia , including the Hawkesbury-Nepean Valley , saw Warragamba Dam spill for the first time in 14 years .

This once again raised awareness about the potential impacts of flooding in major urban areas .

The NSW Government undertook the Hawkesbury-Nepean Valley Flood Management Review ( 2013 Review ) and found that there was a significant existing and growing flood risk in the valley and concluded there was no simple solution or single infrastructure option that could address all the flood risk .

Following the recommendations of the 2013 Review , the NSW Government established the Hawkesbury-Nepean Valley Flood Management Taskforce ( the Taskforce ) in 2014 to develop a wholeof-government approach to flood risk management and preparedness in the valley .

A key objective of the Taskforce was to identify , assess and develop alternatives and options for reducing flood impacts and risks in the valley .

Hawkesbury Nepean Flood Mitigation Action Committee secretary , Maurie Smith , peruses the State Government ’ s Environmental Impact Statement , and likes what he reads . The EIS strongly recommends the raising of Warragamba Dam wall to mitigate downstream flooding .

This included developing the key elements of the Hawkesbury-Nepean Valley Flood Risk Management Strategy for the government ’ s consideration .

In June 2016 the NSW Government adopted the recommendations of the Taskforce , which included a range of targeted outcomes designed to : “ reduce flood risk to life , property and social amenity from regional floods in the Hawkesbury-Nepean Valley , now and in the future ”.

The Taskforce found that the most effective and efficient infrastructure option to reduce the significant risks to people ’ s lives and property from regional flooding is to raise Warragamba Dam for flood mitigation .