Effectiveness and Cost of Coastal Defence

I went to a great lecture on Wednesday at the Royal Society. They have just released a new report all about resilience to extreme weather, including coastal flooding.


They had a really interesting concept that I had not heard before of 'resilience deficit' and suggested that actually many areas are already in this situation of spending money to recover from extreme weather events, rather than spending the money on mitigating or adapting to the extreme weather. This means that in the long run we are spending more that necessary to replace damaged infrastructure, rather than protecting it in the first place.


In terms of coastal flooding they divided the various defensive options up into three categories; engineered, eco-system based, and hybrid, and then produced this graph based on cost and effectiveness.


Source: Resilience to Extreme Weather, The Royal Society

So all the grey circles are engineered defences, the orange ones are hybrid, and the green ones are ecosystem based. The thickness of the circle is about how much evidence there is to support the efficacy of the defence, and the positive signs inside circles indicate that there is another benefit from the defence solution. One of the speakers made the interesting point that people feel disproportionately safe behind engineered defences. In fact while these forms of hard protection are the most effective, when they fail, they fail suddenly. In comparison, the softer forms of protection such as mangroves and beach nourishment, fail more slowly, giving more warning and so more time to come up with another solution.


I think that this is a really great graph because it shows really clearly that while at the moment engineered defences are the most effective, some of the eco-system and hybrid based approaches are not far behind, and in all cases are cheaper. I think it's really interesting that maintainence of mangroves is the cheapest option but is the 5th most effective out of eleven, and has other positve consequences, unlike dykes, levees, and coastal barrages which have no other additional benefits.


To me it also looks like more research needs to go into how effective ecobased solutions are - the green circles are the thinnest of all the ones on the graph. I also think that I definitely need to look more into hybrid solutions for coastal defense - they offer a compromise in terms of cost and effectiveness, but also can come with additional benefits. So I think I will be looking into beach nourishment and artificial reefs in the next couple of weeks.