In Alblasserwaard, problems with water became more and more apparent in the 13th century. Large canals, called "weteringen", were dug to get rid of the excess water in the polders. However, the drained soil started setting, while the level of the river rose due to the river's sand deposits. After a few centuries, an additional way to keep the polders dry was required. It was decided to build a series of windmills, with a limited capacity to bridge water level differences, but just able to pump water into a reservoir at an intermediate level between the soil in the polder and the river; the reservoir could be pumped out into the river by other windmills whenever the river level was low enough; the river level has both seasonal and tidal variations. Although some of the windmills are still used, the main water works are provided by two diesel pumping stations near one of the entrances of the windmills site
