The Port regulating weir at the Nidau–Bürencanal controls the outflow of the Aare riverdownstream Lake Biel and there fore the level of the three Jurassic lateral lakes. Whereas, on the one hand, the levels in these lakes should notrise too high during floods, on the other hand, the outflow of the Aare river should be maintained within agreed limits to protect the areas further down the river. The Water and Waste Management Authority of the canton of Bern is in charge of the regulation and as such must relyon a reliable flow measurement of high availability. A precise measuring system located near theweir should make outflow data available at anytime and ensure that outflow changes can beviewed quickly. For that purpose, an ultrasonic differential runtime measurement system was installed.