Strategische Agenda 2022-2025

18 Water quality and health Hormones, antibiotics and other medicines are produced to make people and animals healthier. But some of these substances go into sewers and ditches and end up in groundwater and surface water, even in areas where the waste water is treated. Excessive concentrations of these substances represent risks for people and the environment. Smart approaches to combining knowledge about these substances, monitoring and simulation models make it possible to show the risks. Monitoring with passive sampling is an effective way of establishing an accurate, early picture of these risks so that the appropriate measures can be taken. These samplers, which are suspended in surface water and groundwater for periods ranging from several weeks to months, allow us to measure even very low concentrations of substances over a long period of time. We can then use software models to predict how the different substances spread through surface water and groundwater. This gives water managers such as water authorities and provincial authorities a better picture of water quality, which contaminants are present, and when contamination actually occurs. As a result, they can take the right measures at an early stage to limit the risk of the contamination of surface water and groundwater. An important benefit of this monitoring method is that it is easy to use in areas that are difficult to access because the passive samplers are easy to transport and they can also be stored for long periods of time. In addition to introducing this approach in the Netherlands, we have also used it, for example, in the CitarumRiver near Bandung on the Indonesian island of Java. That provided us with a picture of how pesticides are used in tropical agriculture and of the use of medication by the local population. That results in important information about the measures and an understanding of the potential benefits for human health. Building with nature is possible everywhere Calls for building with nature are getting louder and louder. We see nature-based solutions, the term used internationally, as the infrastructure for the future. Durable, adaptive and resilient. But what role can nature actually play in reducing the impact of floods, typhoons and tsunamis? How well do trees break waves? Does circular clay work as a material for dike reinforcement? More knowledge can help to protect both nature and people better. Grey/green We often use these natural, green solutions in combination with traditional grey solutions such as dams, dikes and barriers. These are often indispensable but, at the same time, they often disrupt important natural processes or cycles. Dams capture sediment, with downstream erosion and ecological deterioration as a result. In turn, rivers enclosed by dikes transport sediment too quickly to the sea, the surrounding area gets lower and lower, and floods are more likely. Examples of green-grey solutions are vegetation or salt marshes in front of sea or river dikes, naturally ripened dredged material that we re-use for the construction of civil engineering structures, or city parks that we connect to the nearby river or tidal area. Developing knowledge Deltares helps to develop knowledge for the large- scale implementation of nature-based solutions. We do that in our laboratory, experimental facilities or in field experiments. We investigate what happens with water, vegetation and sediment in extreme conditions such as storms or intense rainfall. We always do this in collaboration with our knowledge partners and clients from the field. The technical understanding of the processes in the delta area is the basis for our research but the issues always require a multidisciplinary approach. Chapter 2 Trends and developments