University of Twente Student Theses


Sensitivity of inundation to sea level rise in dike ring 14

Shaffrey, T.J. (2023) Sensitivity of inundation to sea level rise in dike ring 14.

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Abstract:Flood defence in the Netherlands has a long history of disasters, near misses and innovative solutions. The drive to create more arable land and space for its population, all while dealing with low laying elevation has formed an interconnected system of dikes, polders, pumping stations, and storm barriers. After disastrous flooding in 1953 and near misses in the 1990s, much of the modern practice of flood defence was adopted. These measures have led to some of the highest standards for safety in the world, particularly along the coastal areas. Dike ring 14 is one such coastal area and is the focus of this report. Dike ring 14 contains all of the provinces of South Holland, and parts of North Holland and Utrecht. The levels of protection here along the coast are so high, that this has had the effect of reducing the risk of inundation from the sea, at current sea levels, to such low levels that now it is more likely that dike ring 14 would be inundated by the inland river systems. Indeed, it is now assumed that the largest consequences of inundation in dike ring 14 will come from river dike breaches further inland, such as at Nieuwegein. However, with an increasingly unpredictable and unstable climate, the impact of an inundation event from the sea might become worse and worse depending on the extent of sea level rise. This study focuses on the effects of flooding resulting from sea level rise along one of these such coastal areas, dike ring 14 which encompasses large parts of the most densely populated and economically valuable areas of the Netherlands. Meaning what will future sea level rise mean for the Netherlands, and specifically, dike ring 14? To investigate this, the inundation (hazard) and damage (exposure) that increasing sea level rise will have on dike ring 14 will be examined. This will be done with the use of numerical modelling, which combines the one-dimensional (1D) flow of water along rivers, canals, etc., and the two-dimensional (2D) flow of water across the terrain. This 1D2D modelling allows for very accurate simulations to be created that most closely resemble a real-world flood, that would flow across the land, along rivers, and roads. The main aim is to conclude if there is any sea level rise point at which the resulting consequences begin to increase rapidly. To do this these consequences have been split into separate categories, the inundation pattern, such as the area inundated or volume, and the resulting damage in terms of monetary and fatalities estimations. The extent of sea level rise was taken to show more reasonable sea level rise scenarios and also the most extreme cases, these being sea level rise scenarios of 1-5 meters. Four breach locations were investigated under various conditions, such as a breach during normal conditions and another during a storm surge, for increasing amounts of sea level rise. These breach locations were: Katwijk, the Hague, Hook of Holland, and Ijmuiden. These locations were selected to give the most comprehensive result possible within the short time allotted for this research (10 weeks), as while having huge numbers of breach locations would allow for more insight, they would also require significant amounts of time to simulate. All of this was carried out at Delatres, with their SOBEK modelling software which has been used for many years and projects to predict the consequences of flooding. A combination of maps and graphs where used to build up an insight into the scenarios. The inundation pattern, the time at which it reaches certain areas, and the areas with high value that would be affected were mapped. The characteristics of the inundation, the total area inundated, the total volume, the average depth, the estimated damage, and the estimated fatalities were all graphed to see the level of sensitivity of each to sea level rise. The results of all of these show that there is a clear sensitivity to sea level rise, in terms of both hazard and exposure in the event of a dike breach. However, it is also clear that the location of the breach is more significant than the extent of sea level rise as different breach locations change substantially at different sea level rise scenarios. The largest consequences are seen with breaches at Katwijk and the Hague, with the hazard (the total area inundated) being the most substantial from the Katwijk breach, but the highest exposure (damage and fatalities) being from the Hague breach. There are limitations to these findings, as the past simulations focused on lower levels of sea level rise, and thus validation proved difficult. Additionally, the past simulations that could be compared resulted in differences, which could be the result of differences in modelling, changes in digital elevation maps, changes in population distribution, or property valuation. For a more robust result, more testing of different models with similar input conditions should be carried out. This is particularly true of areas around Amsterdam and breaches simulated at IJmuiden, which contains a significant number of assumptions and simplifications that would have impacted the results here significantly. This study found that for dike ring 14, almost all locations are highly sensitive to sea level rise, be it at different rates depending on their location. Further, with 2m-3m of sea level rise a breach from the seaward dikes of dike ring 14 would pose an equal or greater threat than that of past simulated breaches of river dikes.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Programme:Civil Engineering BSc (56952)
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