Dykes & Canals
All the water in the canals, held back by the dykes, is the reason for all of the windmills. A windmill can raise the water level by 10 feet (3 meters). So many times a poulder (reclaimed land) has several levels of dykes and windmills to raise the water to sea level.
Riding on train, it is interesting so see houses with a 6 foot high dyke holding back a canal in their back yard. The water level is above their first floor windows!