Interaction between BOS and BESThe BOS continually assesses the predicted situation against the closure criteria. To this end it gathers data 24 hours a day; every 10 minutes it checks all kinds of information on the environment. These primarily concern forecast water levels, wind direction, wind speed and discharges. These forecasts are amalgamated and converted into anticipated water levels at Rotterdam, Dordrecht and Spijkenisse. After assessment against the criteria this results in a decision as to whether or not to close the barrier. A decision to close the barrier is in principle taken 24 hours before actual closure. The BOS is capable of reviewing the decisions up to three hours before the set time. The BOS converts the necessary steps into commands for the BES.
Apart from implementing commands, the BES is also locally intelligent. Among other things it controls the screw-jacks of the ball-joint, the level of water in the dock, the opening and closing of the dock- gate, the driving in and out of the retaining wall by the locomobile and the sinking and refloating of the retaining wall by the operation of the valves and pumps. In addition the BES controls a number of independent electrical systems, such as the security of the control buildings (access control), the air- treatment in the retaining walls, the ball-joint and the locomobile (i.e. heating, ventilation and air- conditioning). To sum up: the BOS knows the environment, the BES the barrier.