Mardi 8 décembre - Quantitative assessment of coastal risks
de 11:00 à 12:00
Roshanka Ranasinghe, UNESCO-IHE, Delft, Pays Bas
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UNESCO-IHE, Delft, Pays Bas
Titre : Quantitative assessment of coastal risk
It has been reported that about 70% of the world's sandy coastlines are eroding, resulting in gradual and continuous coastline recession. This is driven by chronic processes such as Sea level rise (SLR) and episodic processes such as storm erosion. The rate of coastline recession is likely to increase due to climate impacts such as sea level rise and changing storm wave/surge characteristics. Concurrently, rapid development in the world’s coastal zones continues to increase potential damages, often reducing the resilience of coastal communities. The risks associated with coastline recession are thus very likely to increase strongly over the coming decades, unless effective risk management plans are put in place.
Land-use restrictions are a key component of coastal zone risk management plans. These involve the use of coastal setback lines to define an area along the coastline where development is prohibited or restricted. A setback line that is positioned farther inland will always lead to lower loss probabilities. But foregoing land-use opportunities is costly, making the establishment of setback lines a balancing act. To balance risk and reward, probabilistic estimates of coastline recession are a pre-requisite. Yet the presently adopted deterministic methods for establishing setback lines are unable to provide such estimates.
Here we present a novel quantitative risk analysis (QRA) approach for deriving time-dependent risk estimates. These can be used as a basis for risk-informed and adaptive land-use planning policies, rather than static policies that may well be unnecessarily stringent in today’s environment. The modelling approach presented enables the determination of setback lines in terms of exceedance probabilities, a quantity that directly feeds into risk evaluations and economic optimizations. As a demonstration, the newly developed QRA approach is applied to Narrabeen beach, Sydney, Australia.