Bart Schultz
The Lammefjordpolder is located on the island of Zealand in Denmark. It is land gained from a sea arm at the west side of the Isefjord. The reclamation began in 1873. Large parts were already dry enough a few years later that they could be put into use, but it took until 1943 before the deepest parts of the sea arm were also reclaimed. The surface area of the Lammefjordpolder is 5,760 hectares. Due to subsidence, the lowest surface level is now 7.5 metres below mean sea level. This makes the Lammefjordpolder clearly the deepest polder in Europe.
The Zuidplaspolder in the Netherlands comes in second place. The Zuidplas with a surface area of 6,400 hectares, located between Rotterdam and Gouda, was created by excavating peat for fuel. Due to the vulnerable banks there was a risk of bank erosion and flooding from the resulting lake. Eventually, in 1816, King William I decided to drain the lake. In 1825, the actual draining began, which was completed in 1840. The lowest point in the Netherlands is located in this polder at 6.74 metres below mean sea level. This makes the Zuidplaspolder the second deepest polder in Europe.
Both polders were in fact reclaimed for agricultural land use. The Lammefjordpolder is still predominantly agricultural. This means that gradual adjustments to water management and flood protection are sufficient. However, the Zuidplaspolder is undergoing urbanisation and the construction of greenhouses. This not only increases the population, but also significantly increases the value of buildings and properties in the polder. There is also a serious plan to build another 8,000 homes in this polder in the coming years. This will have far-reaching consequences for water management and flood protection.
Although these are the deepest polders in Europe, they are not the lowest polders. For example, the banks along the Caspian Sea are about 27 meters below sea level. The Volga River also flows into this sea, which is actually a lake. On Google Earth, one can see that there are probably a few polders in the lower reaches and the delta of this river. These would then be the lowest, but they will certainly not be the deepest polders in relation to the adjacent water.
There are also several deep excavations in Europe, which were created during the extraction of minerals. The deepest excavation, as far as is known, is the browncoal mine of Hambach in Germany, down to 293 metres below mean sea level. When the browncoal extraction is completed, this excavation will probably no longer be maintained and will probably become a lake. Something similar probably also applies to the other excavations.
