Bart Schultz
The age of steam engines made water level control possible, and at the end of the nineteenth century, people switched to so-called winter drainage, which aimed to maintain a low polder level even in winter. Initially, these pumping stations took about a day to become operational. At the beginning of the twentieth century, electric and diesel pumping systems were introduced. Initially, the engines could only be switched on and off and were not easily controllable. However, for larger polders, one or more engines could be activated. Later, a number of pumping stations were made infinitely variable, allowing them to be much better adapted to the pumping needs and to better maintain the target water level in the polders.
In polder drainage, it's important that the pumping station can operate at a very limited capacity most of the time. Only a few days a year do the pumping stations need to operate at full capacity to drain excess water. Some time ago, I investigated this for the Noordoostpolder for the period 1945-2006. During that period, the pumping stations could drain a water layer of 15 millimeters per day across the polder's surface. It turned out that this was only the case for a few days. Almost 90 percent of the time, the drainage amounted to no more than three millimeters per day.
Given the aforementioned distribution of water problems, optimization of the drainage system is entirely possible. This is possible partly because weather forecasts have improved, and partly because of the price difference in electricity costs during the day for electric pumping stations. If a dry spell is forecast, drainage can be limited, raising the water level in the polder and making more water available for irrigation. However, water quality must be monitored, as some of our deeper polders, especially during dry spells, experience relatively brackish seepage water, which is unsuitable for crops.
If a wet period is approaching, more water can be pumped out in advance, creating more space for water storage. If not much water needs to be pumped out, this is best done when electricity costs are low. The Zuiderzeeland Water Board has been taking this into account for several years, especially at the main pumping station, De Blocq van Kuffeler. Over the years, various improvements have also been made to the pumping stations themselves, making them more controllable.
Over the centuries, the drainage of our polders has improved significantly, making it increasingly effective and affordable. Recently, the knowledge center for water boards and provinces, STOWA, has organized several interesting meetings under the title "Smart Drainage." Information about these can be found on their website.
In the coming years, further improvements will undoubtedly be made so that, despite ongoing urbanization in the polders, polder drainage can continue to be properly maintained in our country for many years to come.
