Not often to see so clear but this are the vessels of our water controls.
The phenomenon polder is only possible by drainage. Without draining these areas would, lying below sea level, flooding and lakes (bounded by levees) will be that they would otherwise fill up with seepage and rainfall.
Since the invention of windmills in the 15th century, it is possible by pumping to carry water against gravity off. As a result, draining large tracts of land, such as the Haarlemmermeerpolder (and our area) become possible.
In order to make land and arable farming possible in the Netherlands is drainage necessary in order to ensure that the soil is dry (and hence firm) enough to support the heavy equipment. In addition, the constant that the groundwater level for some crops of interest is. Especially for growing bulbs (eg tulips) and fruit is a constant water table is important. And other polders drained agricultural areas, such as wetlands, are among the most productive farmland in the world. In coastal areas for agricultural drainage are favorable in areas with a strong seepage. In these areas often crops out salt water. Through draining the seepage can be captured through which a freshwater lens may arise
More info: https://en.wikipedia.org/wiki/Drainage
Ferry, you're about to be surprised that I know about the ability of the Dutch to drain land and make the soil good for crops, and I know it on a personal level! My great great grandfather founded a town south of Chicago and near the Indiana border, and it was the Dutch people who came over and made the fertile land usable! If you're interested in reading my family history of founding this town and the Dutch involvement, you may find it very interesting! My family name before I married was Danforth. Thank you for sharing that picture!
