All maps on the table

Since the subsurface plays the main role, many of the COASTAR measures take place outside of our field of vision. There is therefore a need to render the invisible visible; a task that Liduin Bos, consultant/researcher at Deltares, dedicates herself to. ‘Based on a data study, we have produced a series of COASTAR measure opportunity maps for the Province of South Holland. These help policy-makers and water managers evaluate the possibilities for the implementation of the COASTAR measures. The maps also offer pointers for engaging in joint discussions about the opportunities that the subsurface presents for the freshwater provision.’

From interfering to combining

The first requirement for the implementation of COASTAR measures – subsurface water storage and brackish water abstraction from groundwater – is a thorough knowledge of the subsurface. ‘This is particularly so, in view of the fact that coastal areas are becoming increasingly congested,’ explains Bos. ‘In many area-development plans freshwater is taking on an increasingly important role with regard to the availability of sufficient drinking water and irrigation water. But the energy transition, the housing challenge, a healthy living environment and recreation also enter the equation. This shows you that more and more functions will be interfering with each other. Many functions also have a connection with the subsurface.

The opportunity maps assist us in laying these functions out next to each other and seeing how they might be combined. This gives you a much clearer picture of the opportunities and of potential impossibilities.’

The opportunity level

Through its association of possible measures with knowledge about groundwater flow, geological stratification and other subsurface processes, Deltares is the expert for production of these schematic maps. Bos: ‘We translate data analyses, model calculations and process knowledge into maps that reveal the “opportunity level” for the subsurface storage of freshwater and brackish water abstraction from groundwater.

Then, in consultation with partners, we combine these maps with other societal challenges being faced in the area, such as drought, local flooding, salinisation and land subsidence. Lastly, we look at the functions in the area, and we combine this information with the water demand and the infrastructure.

This provides insight into where COASTAR measures are of interest and where not, thereby establishing the basis for discussions with the users in the area. The goal is to achieve a single “opportunities map”, in which all the opportunities and risks are brought together. The numerous layers make it possible to conduct discussions with a variety of partners. With all the maps laid out on the table, you can quickly identify where the prospects and bottlenecks are.’

Up-scaling to national level

In her work as project leader for COASTAR nationally, Bos is aware of how important it is to make the implementability of COASTAR measures comprehensible to policy-makers. For example, by indicating where the societal benefits lie and what the implications for water management might be. This information clarifies how the local examples can be up-scaled to the regional and national levels – and therefore what the added value of the measures represents for the Netherlands.

In the area of brackish water abstraction, Bos believes that there are sufficient leads. ‘Two years ago, we used a national hydrological model to research where brackish water upwelling occurs in our country. This concerns many places along the coast. For the Netherlands as a whole, up-scaling of brackish water abstraction could therefore contribute to the drinking water production.’


Now that the pilots in the Province of South Holland are performing better and better, Bos notes that the interest and enthusiasm expressed in other regions is growing. ‘The information is for instance being used by the Delta Programme and it is simultaneously being assimilated into fundamental research proposals. Not all areas are suitable of course. Subsurface water storage for instance depends on the thickness of the underground aquifer. Other subsurface functions, such as aquifer thermal energy storage installations, also need to be taken into account.

The opportunity maps offer a good starting point in answering a wide variety of questions. It is moreover extremely important to engage in discussions with all the relevant stakeholders. Without them, the story remains a theoretical one, with no societal or policy acceptance.

In South Holland we work with all relevant parties: the province, drinking water utilities, water authorities, municipalities and industries such as the greenhouse farmers. For me, this diversity demonstrates that the problems of freshwater shortages, salinization and local flooding are felt by everybody: there’s no way around it. With this kind of opportunity map in hand, COASTAR can provide a solution.’

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