Sea Level Rise Knowledge Programme: insight into the limits of the water system

Introduction

Sea level is rising and this rise is accelerating due to climate change. For the Netherlands as a delta country, this has major consequences for flood safety, freshwater availability and spatial planning. Within the Sea Level Rise Knowledge Programme, HydroLogic provides insight into the viability of the Dutch freshwater strategy.

Duration: 2021–2022
Client: Rijkswaterstaat
Partner: Arcadis
Keywords: sea level rise, salinisation, freshwater, water system, Delta Programme
Models, Tools and analysis: 1- and 3-dimensional salinisation analyses Rhine-Meuse estuary, box model IJsselmeer, data analysis and expert judgement
Collaboration: governments, knowledge institutions and drinking water companies

Background

Sea level rise

The Sea Level Rise Knowledge Programme (KP ZSS) develops knowledge to prepare the Netherlands for sea level rise of up to 5 m. This study investigates the viability of the current freshwater strategy in the Netherlands and how that viability can possibly be increased. Because extreme sea level rise will unfold over a period of hundreds of years, the impact of sea level rise on the maintenance of the freshwater strategy cannot be viewed separately from other developments such as changes in river discharges and water demand.

Method

System analysis

Within the Sea Level Rise Knowledge Programme, this study is aimed at quantifying and interpreting system behaviour under changing conditions. We started from a thorough system analysis and, together with experts, formulated hypotheses on how the functioning of the system changes under the influence of sea level rise. On that basis, a suitable modelling approach was chosen. For some water systems, existing models were used. For example, for the Rhine-Meuse estuary, a combined approach of 1- and 3-dimensional models was chosen to do justice to the different types of salinisation processes in the Rhine-Meuse estuary. For other water systems, a model was set up because the existing models were inadequate for this issue. For example, for the IJsselmeer a 1-dimensional box model was set up with which expected changes in water availability and salinity were mapped out.

For the water systems Volkerak-Zoommeer and Amsterdam-Rhine Canal/North Sea Canal as well, the expected effects of sea level rise on salinisation and freshwater availability were quantified and interpreted. In addition, a supra-regional water distribution tool was set up to map out the possibilities and viability of water distribution via the main water system.

The result

Insight

The results of this study provide a better-founded picture of the consequences of sea level rise for the freshwater strategy of the Netherlands, and thus concrete tools for strategic choices. For the northern edge of the Rhine-Meuse estuary, for example, it was concluded that from a water management perspective there is room to manoeuvre in the current freshwater strategy, provided that measures are taken to make an increase in supply surplus to the freshwater zones HIJ and Lek technically possible.

And for the IJsselmeer-Markermeer, an important finding is that the locks in this area are the largest source of salinisation – a much larger source than saline seepage through the soil under the Afsluitdijk. Already at 1 metre of sea level rise, we see an almost doubling of the amount of salt entering the system.

“The modelling approach was tackled systematically. We now have a good picture of which effects will come into play with different combinations of river discharge and sea level rise, and where the system is more robust than we thought, and where it is not.”

Meinte Blaas | Rijkswaterstaat

What did the project deliver?

Insight into the limits of the current water system
Substantiation of long-term freshwater strategies
Direct input for the Delta Programme and policy choices, at national and regional scale

“In this study, we carried out a first analysis of how much freshwater is needed and, conversely, how much sea level rise the system can handle before adjustments to the freshwater strategy are needed.”

Meike Coonen | Senior advisor