Within days, emergency services were gearing up for a threatening east coast low. Last Friday, long-time coastal engineer and adviser Angus Gordon was on the phone to Stokes, warning, "Rob, I hope I'm wrong, but I think 1974 is coming." He was referring to the monster storm that battered the NSW coast including Sydney four decades ago. Collaroy's beach front houses were among those hardest hit by this year's big storm. Credit:AAP By Sunday, Stokes - as with many across eastern Australia - was fending off rising water levels from the deluge, later telling 2UE: "The full ferocity of nature was just hurled at us and everyone is reeling from it." In his usual low-key manner, Stokes would join hundreds late into Tuesday night laying sandbag defences around exposed homes along Collaroy-Narrabeen's battered shore as the high tide and huge swell persisted. Storm surprises

Coogee Surf Life Saving Clubhouse hit by massive waves during the storm. Credit:Peter Rae Others with an even longer view of the coastal risks, such as Bruce Thom, a professor emeritus at Sydney University, were also out on Sunday, but trying to glean lessons about east coast lows rather than mopping up. NSW typically has seven or eight of the storms forming just off the coast and, depending on how they move, they can expose vulnerabilities - both physical and social. Thom, a coastal geomorphologist, has been accumulating knowledge about the impact of the worst of the tempests since his childhood when an event blew out windows of a nearby school in 1946. Still, last weekend's storm that caused flooding and coastal erosion in a huge arc stretching from south-east Queensland to even New Caledonia and all the way south to Tasmania, bore some surprises too.

Out photographing damage, Thom was impressed by the height of the storm surge within Sydney Harbour that revealed risks facing even relatively secluded coves such as Watsons Bay. "Boats were being pushed onto the shore," he said. Also unexpected was the damage to the Surf Life Saving Club at Coogee, which was built on a rock ledge considered to be out of reach of wave strikes. So, too, the landslip at Waverley Cemetery. "None of us had thought of that," said Thom, who has advised policymakers at all levels for decades including the Baird government, which just last month passed the first overhaul of the state's coastal management laws since 1979. The new act - and the supporting coastal maps and State Environment Planning Policies that Stokes will most likely release later this year - will no doubt receive greater scrutiny after the scale of devastation wrought this week.

Of interest too will be the emerging threat to estuaries, with the Georges and Hawkesbury river mouths among those likely to get more attention. Analysts within Planning and the Office of Environment and Heritage say initial assessments of the damage suggest there is little need to adjust the 15 known hot spots facing coastal erosion from events such as east coast lows. In Sydney they are Collaroy-Narrabeen, Mona Vale and Bilgola Beach. The hotspots are defined as areas where five houses or more, or a public road, are at an immediate risk from a major storm, according to a 2010 assessment. Most studied beach Water laps at properties on Sydney's coast on Monday morning. Credit:Bankstown Helicopters

Despite the media focus on the strip of houses crumbling into the sea at Collaroy and Narrabeen on Sydney's northern beaches - and the subsequent red-hot blame game over an approved sea wall that wasn't built - the focus of the impact was one of the least of the surprises from the tempest if not perhaps for some of the residents. "The areas where the worst erosion occurred in the June 2016 storm event were within coastal erosion hot spots," the OEH told Fairfax Media. In fact, the Narrabeen-Collaroy beach is among the most studied parts of the Australian coast because of its peculiar combination of vulnerability and settlement patterns. Coastal engineer Ian Turner, director of the Water Research Laboratory at the University of NSW, says there was "absolutely no surprises" about the damage the high tides, fanned by the storm system, had wreaked on the beachfront properties. The beach had been monitored for about 40 years, more intensely than any other in Australia, he said.

Giant event Collaroy beach narrowed by 50m. Credit:Peter Rae The forces of nature on show were remarkable. The Narrabeen-Collaroy beach narrowed by as much as 50 metres and surrendered about 400,000 cubic metres of sand to the seas. Although the known erosion hotspots account for just 30 kilometres of the state's 2000-kilometre coastline - and perhaps 200 high-risk properties - the damage bill can still be huge. And as OEH told Fairfax Media, the frequency, intensity and duration of storm events are predicted to increase due to climate change, so threatened areas are likely to swell in number and size even before expected population growth along our much-loved coasts.

"Wherever there are houses sitting on the sand dunes in Sydney, it's just as likely to happen [as last weekend's storms]," Turner said. "It's up and down the whole Sydney coast - wherever there is infrastructure, be that roads or surf clubs or power lines." Wettest day on record Homes and public assets certainly came in for a huge hammering, not least from the the sheer volume of rainfall dumped along Australia's coast. "It looks like, on an area-averaged basis, eastern NSW had its wettest day on record [for the 24 hours to 9am on Sunday]," Blair Trewin, a senior climatologist at the Bureau of Meteorology, said. Of NSW's 20 coastal river catchments, 19 recorded at least 70mm of rain on Sunday alone, with only the Hunter flowing into Newcastle spared.

"It think it would be highly unusual, perhaps unprecedented," Trewin said, adding that most east coast lows generate more tightly centred storms, affecting a 200-300-kilometre range at one time. Trewin noted warmer than average sea-surface temperatures increased the amount of moisture available for the storm to tap, creating sub-tropical conditions quite abnormal for early winter. Indeed, sea-surface temperatures for May in the Tasman Sea were unprecedented. (See bureau chart below of temperature deviation from the long-term averages.) Temperatures on land were also exceptionally warm during the height of the storm, with Sydney's 16.3-degree minimum on Sunday likely to be among the city's 10 warmest on record for June.

Further south, Launceston, Hobart and a slew of other Tasmanian sites notched record warm overnight temperatures on Monday, Trewin said. Climate researchers, such as Acacia Pepler, a PhD student focusing on east coast lows, say that a warming planet will most likely reduce the number of such storms at least during winter. That's because conditions for their formation will be less favourable as parts of the atmosphere become more stable. However, as the atmosphere can hold about 7 per cent more moisture for each degree of warming, rain from storms is likely to become more intense when they do form, scientists say. Storm surge The weekend's storm had other special features that amplified its impact. Though spawning less powerful waves than the 1974 blast, the damage was made worse because the recent storm coincided with the highest tides of the year, Alex Zadnik, a meteorologist with Weatherzone, said.

The seven-metre swell generated by the storm as winds piled the waves up was topped up by the 2.05-metre tide, as well as a roughly 25-centimetre storm surge linked to the low pressure. (Each drop of 1 hectopascal of atmospheric pressure lifts local sea level about one centimetre.) The direction of the waves from the north-east - including the longevity of the event - was also unusual. (See chart below showing how the swell's generation zone extended approximately 1500 kilometres from the Coral Sea to the NSW coast.) "The north-east to easterly waves observed over the weekend are the largest ever recorded from those directions offshore of Sydney, which has one of the most extensive long-term records of directional waves in the world," David Taylor, managing director of engineering firm Baird Australia, said. While the nor'easterly winds and waves were unusual, their impact on beaches such as Collaroy-Narrabeen was much as might be expected, said Angus Gordon, an engineer who oversaw beach replenishment efforts after the 1974 storm and has advised Stokes on the new coastal management plans.

An offshore kilometre-long sub-sea reef about five to eight metres high "serves as a very large lens" to refract the waves onto known parts of the nearby beach, Gordon said. "The community memory fades … we don't have regular disasters," Gordon said, likening the tendency to building in areas known to be at threat from floods or bushfires. "It's one of those societal problems - people just believe the risk doesn't exist." 'Wicked' problem NSW Planning Minister and the member for Pittwater Rob Stokes. Credit:Steven Siewert Stokes has sought to address a range of those issues as architect of the new coastal bill, which subtly replaced "protection" from the 1979 act's title with "management".

The minister brought notable expertise to the role. As a former planning lecturer at Macquarie University, he wrote papers on the "wicked" planning problems facing areas such as Narrabeen in 2003 and 2011 and has lived much of his life in the area. "If you went back 100 years, none of these houses would have been here [knowing what we know now]", he told Fairfax Media. The new act, which passed Parliament without a division, is ambitious. For the first time anywhere in the world, Gordon and Thom said, the act takes into account both the offshore sand and other sediment formations, and the natural beach fluctuation. The coastal strip will also be mapped to identify vulnerable areas as well as vital assets such as remnant rainforests and wetlands that must be conserved - ideally done well before another major storm. Councils will have access to $83.6 million over five years to develop management programs that will be audited by an expert panel reporting to the planning minister.

Importantly, the plan will also extend to estuaries - where the number of homes at risk from floods linked to east coast lows is at least 10 times the 200-plus houses known to be at direct threat from coastal erosion. Climate change will amplify those threats too. "In the past, we never had cost-benefit analyses underpinning the decisions," Stokes said. "Now [councils] will have to do them." That means, for instance, if a community wants a sea wall it will have to determine who benefits and who pays, including for the beach replenishment likely to be required over time. Sometimes - but not always - benefits of a wall, including added protection to local residents and key public assets such as roads, will outweigh the distorting effects on waves that would potentially expose other areas to risk. Past errors

What the government wants to avoid is repeats of past errors when, particularly after a major storm, locals threw up poorly designed structures or even deposited boulders or sandbags that merely turned into hazards in the next tempest. Thom, for instance, recalls councils in the 1970s dumping hundreds of car bodies in futile attempts to protect the beach, only to introduce beach hazards that can remain for decades. For Collaroy resident Garry Silk, the changes have come a couple of years too late. Silk said that, when he bought his waterfront home in 2013, he was aware of the risks but hoped a uniform sea wall would soon be installed by the council. By midweek, Silk had not been able to examine the full extent of the damage to his property but knew his garden was destroyed and his balcony left hanging after the high tides. There is no sea wall in front of Silk's home and he believes the individual barriers that residents had built over past decades had increased the impact of the tides on his property. He had been willing to contribute to a new wall if councils and residents had been able to agree."I'm upset, but the past is the past. Clearly we would have liked it to be done before but the reality is it hasn't and now is the time to act," Silk said.

Cluster risk Time may become an issue in other ways that could expose the state's vulnerabilities. East coast lows are most frequent in June, and another big storm in coming weeks is possible before beaches naturally recover and flood-hit catchments dry out, raising the risks to known or unknown threats. Sydney's reservoirs are also sitting at about 97 per cent full, including the giant Warragamba Dam.

"This is the time of the year when we are mostly likely to have a big east coast low," Pepler said, noting June 2007 had five such events, including the storm that sent the Pasha Bulker ship ashore near Newcastle. "If we saw another storm of [last weekend's] intensity in the next couple of weeks we would have some significantly serious issues right along the NSW coast," Geoff Withycombe, Sydney Coastal Councils Group executive officer, said. Weatherzone is owned by Fairfax Media, publisher of this website.