The drained lakes in the Netherlands

When I had been working for some time at the Water Management Department of the Scientific Division of the IJsselmeerpolders Development Authority, it was suggested that I considered a topic for a PhD study. I was somewhat surprised, because at that time it was very unusual for civil engineers to consider doctoral research. However, it was much more common in the other disciplines within the Scientific Division.

I then started thinking and arrived at the conclusion that I could develop a computer model to optimize the water management system for the Markerwaard Polder, which was then in preparation. This model weighed investments in the water management system against yield reductions in agriculture and damage to buildings and infrastructure. In doing so, I felt that I first needed to look at the history as well. My doctoral research therefore followed two tracks: history and optimization.

There are quite a few polders in the Netherlands, so the history of the three types of polders would become a research project in itself. In consultation with my potential supervisor, it was decided that I would focus solely on the water management of the drained lakes. After all, the proposed Markerwaard Polder was also going to become a drained lake, just like the other IJsselmeerpolders.

When I started my research, besides the IJsselmeerpolders, I knew of some forty drained lakes: the Beemster, Schermer, Purmer, Wormer, Haarlemmermeer, and numerous others. By the time I finally obtained my PhD, I had mapped 445 of them. This had therefore been a considerably larger undertaking than I had initially envisioned. However, I have never regretted it and am now conducting further research into polders around the world at Museum Batavialand. This is research that I will never finish, because I keep finding more.

A distinction can be made between drained, more or less natural lakes and drained excavated peatlands. The former group comprises 242 polders with a combined area of 227,008 hectares. There are 203 drained excavated peatlands with a combined area of 84,700 hectares. The distribution across the provinces in which the polders are located is shown in the table.

Table: The drained lakes in the Netherlands

In a previous contribution to Flevolands Geheugen, I wrote about seepage in the polders in the Netherlands. Although seepage in drained lakes is generally less than 2 millimetres per day, it is still significant. A seepage of 1 millimetre per day is, on an annual basis, roughly equal to the average annual precipitation surplus. The advantage, however, is that it is very consistent and therefore does not have the peaks we experience during extreme rainfall. However, it does lead to a doubling of the annual amount of water to be pumped out.

Virtually all drained lakes were created for agricultural land use. However, particularly after the Second World War, there has been significant urbanization within the drained lakes. It is estimated that around one million houses will need to be built in the Netherlands in the near future. A significant portion of these will be located in the drained lakes. In this context, it will be important not only to properly integrate urban expansions and potentially entirely new cities within the drained lakes from a planning perspective, but also to adapt water management systems and flood protection provisions in a timely manner to urbanization and the expected consequences of climate change.