Bart Schultz
Together with Polder de Koekoek near Kampen and the Bethunepolder near Utrecht, the polder is one of the polders in the Netherlands where a great deal of seepage - upward groundwater flow - occurs. In the Horstermeer Polder, it is about 15 millimetres per day calculated over the area of the polder. For the vast majority of other deep polders in the Netherlands, the seepage amounts to no more than two millimetres per day.
The average annual precipitation surplus compared to evaporation amounts to about one millimetre per day. In these three polders, there is therefore an extreme amount of water that has to be pumped out. As far as the Horstermeer Polder is concerned, this seepage is mainly caused by groundwater flow from the Utrechtse Heuvelrug and the thin, poorly permeable top layer of clay and peat that exists in the polder.
The Horstermeer was a more or less natural lake in the middle of peat bogs. Permission to drain the lake was granted by patent of 19 February 1612. Based on this, the first attempt to drain the lake with windmills started that year. In 1629, the polder was finally dry, but due to problems with the large amount of seepage, the pumping was stopped in 1649 and the polder was inundated again. In 1882, the polder was drained again with the help of a steampower pumping station and has been kept dry ever since.
In 2009, I became involved with this polder by chance. At that time, I organised an annual polder tour for foreign students of UNESCO-IHE in Delft. We started at the very interesting archive of the Principal Water Authority of Delfland and then travelled via the Cruquius Museum and the series of windmills at Schermerhorn through the characteristic types of polders to end up in the middle of the Horstermeer Polder. Here I explained that you can see from the multitude of open drains that it is a special polder with a lot of seepage.
In 2009 a few residents came to me and asked: "What are you doing here?" I told them that I was explaining to foreign students that this was a special polder.
"Sir, do you know anything about water?"
In short, we started a conversation and the residents told me that the Province of North Holland wanted to inundate the north and south sides of the polder for nature development. I was quite surprised about that, because this polder did not seem very suitable for such a purpose. I made an appointment with the residents for a meeting and this lead to my being involved with the Horstermeer Polder up to this day.
The residents explained to me what the province's plans were and told me that they were quite concerned about these plans. They had also already formed an action group. I promised that I would try and figure out for them what objections could be raised against these plans. This has led to various presentations and discussions. Ultimately, a so-called scientific committee was set up by all those involved, which essentially led to the following proposal:
- raising the water level on the northern side of the polder has been cancelled;
- in the southern nature reserve the level was raised, but movable weirs were installed so that the polder water was not additionally burdened during extreme periods of precipitation;
- the pumping station of the polder was made infinitely variable. This meant that the engines could run at different capacities, which meant that the water level in the polder could be better regulated - less level fluctuations.
In the meantime, a number of years of experience have been gained with the new situation. The water management in the polder is indeed being better regulated. In the meantime, however, it has become apparent that the organisations responsible for the nature reserve in the southern part are not satisfied with the way the flora and fauna are developing and new measures have been proposed for this area. It is of course again important that these measures are designed in such a way that the water management situation in the Horstermeer Polder does not deteriorate again.
In August 2022, the 140th anniversary of the polder was enthusiastically celebrated by the residents. The Horstermeer remains an interesting, but vulnerable polder, where good water management tailored to the specific situation of the polder is of major importance.
