By ECE student Lye Cheng
On 15 Nov 16, we had the privilege to have Dr Thomas Wahl to share with us on the formulation of the extreme sea level rise and its effect on coastal adaption.
Thomas started by explaining how extreme sea level rise will have significant societal impacts as approximately 40% of the population stays within 100km of the coast.
Firstly, he brought us through the derivation of the return period. We would need to examine the historical data from the tidal gauges, select the maximum annual tidal level and rank the observed events. For the formula enthusiasts, here comes the equations to derive the empirical probability of the return period.
P(probability of event) = Rank / (N+1) N=total no. of max. annual tidal level
Return period = 1 / (1-P)
There are other ways to derive the return period such as gumbel distribution, generalized extreme level, etc. However, the important thing to note is that we should always account for the uncertainties in our derivations.
After determining the return period, storm surge models (eg. DINAS-COAST & Global Tide and Surge Reanalysis) are used to understand the coastal system. Something to be aware of is to factor in the land rise in some part of the world when deriving the relative sea level rise. Uncertainty in the model can be narrowed by calibrating it with the observational data.
In conclusion, the policy makers would make the decision on the sea level rise criteria to be adopted in the design manual of the individual countries. As engineers, we should understand and refer to the correct design criteria before embarking on our design!