Student Use Case: Water on the wrong side of the levee

Student Harro Jongen from Wageningen University has used the Tygron Platform for his internship and thesis, as part of the bachelor’s program “International Land and Water Management”. For a case in Arnhem, he investigated the damage that water can cause to dikes due to wave overtopping.

By: Harro Jongen Education: Bachelor International Land and Water Management, Wageningen University Commissioned by: Tauw

Introduction

In 2017, new standards for dikes were introduced in the Netherlands. One of these new standards was to increase the permissible flow rates during wave overtopping. In practical tests, dikes and especially quays turned out to be much more resistant to erosion than was thought earlier. This meant that, in some cases, flood defence may be lower than the old standards allowed.

What was not included in this standard is the damage that water causes once it is on the wrong side of the dike. This was because the size of the damage, if water had already reached the wave overtopping point, was not yet known. These events are relatively rare because for that to happen, a high water level must coincide with strong winds from the normal direction.

During my internship and thesis for my bachelor “International Land and Water Management”, I looked at the damage that this water could create. First I looked for places where this problem may arise. I ended up using a case in Arnhem.

Analysis

In the beginning of my research, I investigated where such problems can occur in the Netherlands. After an analysis of literature and elevation maps, I selected a number of locations, and from those locations I have chosen Arnhem.

This is when I started using Tygron. Tygron’s flooding tool was originally designed to map rain overload. One of the functions of this tool is the ability to assign a flow rate to outlets in your area. This allows water to leave the calculation area. If you assign a negative flow rate to these points, water will flow into this area. To simulate wave overtopping, we created points of this kind along the entire quay.

Implementation

Using this method, we have examined where the water in Arnhem would flow to in different scenarios. The figure below shows what could happen in the event of a flood, that could occur once every 4000 years, at a quay height of 14.65 meters above the sea level. As seen in this situation, a significant part of Arnhem would be flooded. Therefore the study concluded that the future design quays must take into account the wave overtopping and its potential consequences.