The Demer

Here we are at the Demer, one of the most important rivers in Flanders. This river springs in Ketsingen near Tongeren and flows 85 kilometers further where it merges with the Dijle, at the height of Werchter. As mentioned before, not a drop of water from the Demer flows into the retention basin 'Webbekoms Broek'. The Demer is a rain river. As the term indicates, the amount of water that is discharged is primarily determined by the rainfall pattern rather than by springs. Springs have a relatively constant flow rate of underground water supply. For rain, it is entirely different.

The rainwater is drained to lower areas via the streams on the surface. When the soil has few sponge-like properties and the vegetation is also limited in its presence to slow down the flow, the river will quickly fill with water and will not have sufficient capacity to carry this water away during heavy rainfall. Flooding is the result. On the other hand, during dry periods, the flow will decrease so much that navigation becomes impossible and even water mills have difficulty keeping turning. Today, this economic importance is no longer relevant, but in the Middle Ages, until the railways were established in the 19th century, the Demer was an important transport artery.

Jan Rymenams