Bart Schultz
Looking at the size of the polders, the Polder Flevoland in the Netherlands, is probably the largest, with a total area of 97,000 hectares. The dike in Eastern Flevoland was closed in 1956, and the dike in Southern Flevoland in 1968. The two parts of the polder are now openly connected via the movable vertical gates in the Knardijk at the intersection with the Lage Vaart and Hoge Vaart canals.
After the completion of Southern Flevoland, the Knardijk served as a so-called dormant dike, functioning as a regional barrier by closing the vertical gates in the event of a disaster. However, in 2016, the Province of Flevoland, on the advice of the Water Authority Zuiderzeeland, decided to discontinue the Knardijk's function as a regional flood barrier. However, the Knardijk still serves an evacuation function, meaning that in the event of flooding in one part of Flevoland, the incoming water is slowed sufficiently to allow the other part of Flevoland to be evacuated in time.
The first land reclamation project in Europe was probably the reclamation of Lake Copais in Greece in 1300 BC. This lake was located northwest of Athens in a depression 95 metres above mean sea level. It was fed by rainfall and the waters of the Boeotian Cephisus and Melas rivers. Excess water from Lake Copais discharged approximately three kilometres to the sea through 23 natural caves.
Around 1300 BC, the river waters were diverted through a 25 kilometres long canal to an underground passage. The resulting dry land was reclaimed, surrounded by dikes, provided with watercourses, and cultivated. However, the system fell into disrepair. Between 334 and 331 BC, an attempt was made to reclaim the newly formed lake, but this effort appears to have failed. Ultimately, 20,000 hectares of Lake Copais were reclaimed between 1886 and 1887.
The highest polder in Europe is probably the reclaimed Lago di Fucino in Abruzzo, Italy. This lake lies 668 metres above mean sea level. The lake originally had a fluctuating surface area of approximately 14,000 hectares and regularly flooded the surrounding land. At the initiative of the Roman Emperor Claudius I, the surface area of Lago di Fucino was reduced to approximately 9,000 hectares in the first century by digging a 5.6 kilometres long tunnel. By later extending and deepening a 4.5 kilometres long canal, the lake's surface area was further reduced to approximately 5,700 hectares. However, all attempts to reclaim the lake were in vain.
Between 1852 and 1862, a larger tunnel was built along the same route as the Roman tunnel. The work to reclaim the lake was then successfully completed by Prince Alexandro Torlonia. Reclamation of the lake began in 1862. In 1870, the new tunnel and the reclamation work were completed.
The deepest polder in Europe is the Lammefjordpolder in Denmark. In this 5,600 hectare coastal polder, the lowest part lies 7.50 metres below mean sea level. This polder was reclaimed between 1873 and 1875 with contributions from Netherlands specialists and constructed behind a 2.4 kilometres long enclosing dam in an estuary.
The lowest polder in Europe is probably located in the Delta of the Volga River near the Caspian Sea. It's difficult to determine exactly how low this polder is, but it must be around 27 metres below mean sea level.
Between these extremes of polders lies a multitude of other polders. Our ancestors often created these under very difficult circumstances. Continuous, careful management and maintenance, as well as improvements in the water management systems and provisions for flood protection, will be necessary to keep the polders timely in a good condition.
