Deltares conducted research into the relationship between Rhine and Meuse discharge on the one hand and the occurrence of water intake problems for drinking water companies on the other. Many factors determine whether an intake closure is necessary. This makes a direct relationship between low river discharge and the number or length of intake closures difficult to demonstrate. But during prolonged droughts, the impact of any closure will be greater because the closure will last longer.
Previous studies (e.g. Van Vliet and Zwolsman 2008) show that water quality is negatively affected by summer drought. The decline in water quality during summer drought is related to both high water temperatures and low discharges. Looking only at the discharges, only some industrial chemicals show a direct relationship with the discharge, according to Deltares. For many other substances, no relationship was found; several processes are at play there;
- the degradation process depends on the water temperature,
- during a low-water period there is often little precipitation and thus less leaching,
- emissions depend on the application period.
It is therefore not trivial that more intake stops can actually be expected during low water. This does not detract from the fact that during calamities, the size of the discharge does matter, during low discharges, emissions have an impact on water quality for a longer period and thus on the duration of intake stops.
Looking ahead, KNMI predicts that low-water situations will become more frequent. Besides discharge, the number and duration of intake stops will depend on emissions, water temperature, post-purification possibilities and the occurrence of calamities.
