ENCROACHING TIDES OR VENICE EFFECT

Some years ago after a visit to Venice, I wrote about the process of increased frequency of high tidal inundation as sea level rises.

I called this the Venice Effect.

Over the last 60 or so years the number of days per year when Venice was affected by tidal inundation has increased several fold. This made a big impression on me as I also observed the various costly engineering works being used to mitigate the impact of such increased frequency.

I was reminded of this issue earlier this month when I was shown a report from the US Union of Concerned Scientists entitled Encroaching Tides: how sea level rise and tidal flooding threatens US East and Gulf Coast Communities over the next 30 years (click link to download). The report highlights places that are at the “front lines of tidal flooding” such as Annapolis, Florida Keys, Miami, South Jersey Shore, Charlestown. Today many communities are already seeing more frequent flooding during high tides. In many locations, these floods are happening much more often than just 40 years ago. In some communities, tidal flooding has quadrupled in frequency since 1970. And on top of this, there have been extreme events such as Hurricane Sandy which have led to very damaging and extensive inundation of property as a result of storm surges. Even this year, the snow blizzard across the northeast US coincided with flooding of low-lying coastal areas.

Analysis of tide gauges shows how these communities can expect a steep increase in the number and severity of tidal flooding events over coming decades with adverse consequences for property, infrastructure and daily life. This analysis  is linked to longer term trends in rise in both global and regional sea levels, noting that for parts of the US east coast sea level is rising at a higher rate that the global average. The report notes by 2030 more than half of the 52 communities studied are projected to experience at least 24 tidal floods per year assuming moderate sea level rise projections. However, 20 of these communities could see a tripling or more in tidal flooding events. But extend the projections out to 2045 and the numbers change dramatically: one-third of the 52 locations face flooding more than 180 times per year without extreme weather events, and nine locations including Atlantic City could see tidal flooding 240 times a year.  This is looking a lot like where Venice has been heading.

www.witnesskingtides.org

The challenge, of course, like Venice, is how best to prepare for what looks like the inevitable around the Australian coast. Some years ago Phil Watson inspired us to take photos on king tides to register levels the sea is reaching. I hope we are continuing this practice. I am at Parsley Bay. This gives us some idea of what is happening even though I expect it will be at a slower rate than the US east coast. But the need for planning and management of at risk areas is an imperative.

Many efforts are already being made to alert communities to the risks associated with inundation. And this must continue. The US report referred to above calls for a coordinated, well-funded federal adaptation response as the costs and challenges will turn out to be too great for municipalities to shoulder alone. But in a sobering conclusion given the extent of exposure along the east and gulf coasts of the US: “ there is a hard truth about adaptation, it has fundamental limits—whether physical, economic or social—and it can only fend off the impacts of sea level rise to a point”.

Words by Prof Bruce Thom. Please respect Bruce Thom’s thoughts and reference where appropriately: (c) ACS, 2016, posted 15th February 2016, for correspondence about this blog post please email admin@australiancoastalsociety.org.