Assessment of changes in flood risk in South Holland due to sea level rise

Assessment of changes in flood risk in South Holland due to sea level rise: How can the dunes of dijkring 14 cope with sea level rise?

Meyer Ranneft, Marijn (TU Delft Civil Engineering and Geosciences; TU Delft Hydraulic Structures and Flood Risk)

Kok, M. (mentor)
Lanzafame, R.C. (graduation committee)
Rutten, M.M. (graduation committee)
Bos, Matthijs (graduation committee)

Delft University of Technology

Civil Engineering | Hydraulic Engineering | Hydraulic Structures and Flood Risk

2020-12-16

Economic risk due to a potential flood event is determined by combining the estimated damages and the probability of failure for many scenarios. In recent research of the IPCC (Intergovernmental Panel on Climate Change) it was stated that the sea level will rise more than expected due to climate change . This could influence the flood risk in coastal areas including the Netherlands. In this thesis the influences of the sea level rise on the flood risk for dijkring 14 will be evaluated. Dijkring 14 is located in the coastal area of the Netherlands and contains Rotterdam, the Hague and parts of Utrecht and Amsterdam. It has 3.500.000 inhabitants, consists of an area of 224.000 acres and has the largest potential economic damages. The average elevation of the dijkring is one meter below NAP. The coastal area is protected by hydraulic structures and dunes which are both subjected to an increase of probability of failure due to sea level rise. In this thesis it is assessed if the protection of the coastal area by means of dunes is possible in case of an extreme sea level rise future scenario. With an hydrodynamic flood simulation future flood events dominated by extreme sea level rise are simulated. The hydrodynamic flood simulation is executed by Delft3D Flow FM. In D-Flow FM the unsteady shallow water equations are solved based on the Navier Stokes equations. It solves in 2 dimensions with an average water depth per grid cell. This results in accurate water flow over land. The hydrodynamic flood simulation is verified by comparing the result of the current scenario with the the widely accepted VNK2 model. The validation is executed based on a visual comparison, a inundation depth comparison and a comparison of the estimated damages. This assessment was done for three different breach locations and resulted in a reliable hydrodynamic flood simulation. To estimate the damages that occur during a flood event that is simulated by the hydrodynamic simulation, the Global Flood Risk Tool was used. This tool combined the inundation depth, the land use map and the damage curves and created a damage map. This map represented the estimated damage per area which resulted in a total estimated damage per flood event. Flood risk is determined by a combination of estimated damages and probability of failure. With the hydrodynamic simulation and the Global Flood Risk Tool, damages were estimated for three breach locations and five different future extreme sea level rise flood scenarios. This resulted in a damage estimation for sea level rise scenarios up to two meter rise. The probability of failure is estimated by means of the height that is needed to decrease the probability of failure by a factor ten. Economic optimisation was used to determine the economically optimal probability of failure for each of the scenarios. With the economic optimisation, the cost and benefits of the investments needed to increase the the probability of failure are calculated. These optimal probability of failures were compared to the minimal required probabilities of the 'waterwet' of the Netherlands to determine if the investment is economically acceptable. For two of the three locations it became clear that investing in strengthening the dunes of the coastal area of dijkring 14 is economically acceptable. The third location resulted in a slightly smaller optimal probability of failure. When estimating for the whole coastal area of dijkring 14, it becomes clear the defending the dijkring against flood risk by use of the dunes is possible in future extreme sea level rise scenarios.

Flood Risk
economic optimisation
D-Flow FM
Flood simulation
Hydrodynamic model
Coastal flooding

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Student theses

master thesis

© 2020 Marijn Meyer Ranneft