Steven Kaptein

The Volkerak-Zoommeer is a body of water in Holland facing ecological problems for years. It is connected with the Hollands Diep by the Volkeraklocks and with the Krammer by the Krammerlocks. As the Krammer is a saltwater area and the Hollands Diep a freshwater, it is difficult to keep a constant salinity in the Volkerak-Zoommeer. During dry periods, cyannobacteria can grow in it. The only way to deal with this issue is to brackish the Volkerak-Zoommeer water to a higher salinity. Thus, the salt-fresh interface is moved from the Krammerlocks to the Volkeraklocks. One condition of this change is to limit the salt intrusion in the Hollands Diep through the locks.

The interfaces between saltwater and freshwater (for example in locks or estuaries) are the place where saltwater may enter the inland. The difference in densities between saltwater and fresh causes gravity currents: the heavier saltwater flows under the lighter freshwater. A possibility to limit this saltwater current is to use bubble screen on the bottom of the lock chamber. The air bubbles, mixing with water create an upward flow, which can reduce the salt intrusion.

Shin (2004) found an analytical solution for the speed and the depth of the heavy water current. We can use this result to estimate the quantity of salt which is entering the lock chamber each time the doors are open.