At what point does the current change direction in an estuary? Research conducted within the Chair in Hydrology, in collaboration with the department of remote sensing (both in the Faculty of Civil Engineering and Geosciences) has demonstrated that the position of a buoy in relation to the direction of a river current can provide a clear image of this change in direction.
In an estuary, the change of current direction takes place twice daily: at ebb and flood. During the approximately 15-minute period when the shift is taking place, there is almost no current in the area. According to the hydrology researcher ir. Wim Luxemburg, it is helpful to know when this period of slack water occurs. ‘For example, this could be useful for towing companies trying to release a stranded ship. That can best be done when there is no current. The point at which the shift occurs is also an important parameter for models describing the change in salt content during a tide’.
Businesses, shipping companies and scientists are now only able to estimate when the shift in current will take place. ‘Based on models, it is harder to make an accurate prediction of the current than it is to predict water levels. This is because the period of slack water does not correspond to the highest and lowest water levels. In the Westerschelde, it can occur up to an hour later’. Simple GPS devices on buoys that are already in the water can be used to follow the change in current direction as it takes place. The buoys float along with the current. Taking their position as a starting point, it is possible to calculate when the shift will occur. Luxemburg notes that further research is needed on the operationalisation of the method. Time will tell whether a commercial funding source will see any profit in the idea.