Water management in Friesland

Since 2004, water management in Friesland is in the hands of one organization, the Wetterskip Fryslân. The greatest concern in the future is sea-level rising, which will make it difficult to discharge excess water on land into the sea. The first form of water management started in the 10th century when the ring dikes were constructed to protect the villages and surrounding land from the sea. Excessive freshwater had to be able to get out of the polders.

Excess water is pumped out of the polders and into the Frisian drainage pools with the help of 800 polder pumps. The most important transport canal for the drainage pools runs through the sluices by Harlingen and Dokkumer Nieuwe Zijlen. The water eventually ends up in the Wadden Sea, which presently occurs under free fall, or in other words, gravity. Water can also be discharged into the IJsselmeer via electrical pumps, which pump the water into the higher-lying body of water. Because the sea level is rising, there are thoughts of building extra pumps in Friesland to remove excess water. Raising the summer level also helps. Other challenges for Friesland are bottom subsidence due to such activities as gas and salt exploitation (land subsides so dikes must be made even higher) and soil becoming salty due to seepage from under the dike.

The European Water Framework Directive was devised in order to obtain a good ecological and non-polluted situation in surface waters. To suffice the directive in Friesland, special attention must be paid to eutrophication from agriculture and horticulture, the burden of surface and groundwater from sewage overflow, emissions of heavy metals and PCBs and groundwater pollution from nutrients and pesticides.

From terpen to polders

The first inhabitants of the wadden coast in Friesland lived on terpen. The terpen were later connected by dikes, creating a safe passage. Only in the 9th and 10th centuries were the first true dikes constructed, whereby land was protected from the sea. In Westergo, the first ring dikes were built around the polders in the 10th century, which were managed by villages and districts ('grietenijen'), the predecessors of the municipalities. The ring dike around Pingjum in Friesland is a good example of such an earlier dike. It is known as the Pingjumer Halsband ('collar') or the Golder Halsband. These ring dikes were later connected together, so that large regions were protected from the sea. Around the year 1000, in order to protect the land beyond from the sea, a dike was constructed around the Middle Sea, an inlet of the Wadden Sea.

In the beginning, individuals were responsible for managing the dikes. The larger the piece of land a farmer owned, the more dike he had to manage. Therefore, he had to let officials know how much land he owned. If it appeared during a check that he claimed too little, than the land was taken away from him. Sometimes, it also occurred that a farmer found the costs of managing a dike not worth the profits from the land. In that case, the land was also taken away by the church or the township, who could redirect the ownership.

The early days water management

Existing creeks and channels were first used to get rid of excess freshwater in the polders. Part of the channels were dammed and other parts were provided with sluices which veered the seawater and discharged excess freshwater. In the Middle Ages, these natural channels were deepened and widened. A major amount of the discharge in Friesland was carried via sluices in the dike to the Middle Sea, a sea inlet of the Wadden Sea in those days. After the Middle Sea was closed off to the Wadden Sea in the 16th and 17th centuries, new waterways were dug or old creeks were deepened even more, so that the water could find alternative ways. Many waterways in Friesland were only connected together with canals in the second half of the 20th century.

The rise of the windmills

Before there were windmills in the polders, the water level was regulated with the help of sluices. Water could only be discharged into the drainage area when the level outside of the polder was lower. Windmills suitable for pumping water were first built in Friesland around 1500. Lower lying regions could then be converted into polders. The farmers could establish their own polder level in every individual polder, and the water level could also be well regulated on a small scale. An estimated 1500-2000 windmills were built in Friesland in the course of time.

The Frisian Boezem

As the number of polders grew, the Frisian boezem had to process more and more water. At the same time, wet regions were being reclaimed, whereby the boezem continued to decline in size. The result was a lack of space for all the water. To solve the problem, many ditches, canals and waterways were dug to provide sufficient drainage. The Frisian boezem originally consisted of various units. The water level in Oostergo was independent of that in Westergo. In the 19th century, the boezems were linked together so that ships no longer encountered drainage sluices.

Tidal floods

Over the centuries, the sea dikes in Friesland were broken through a number of times during tidal floods, sometimes resulting in thousands of deaths. The disasters were caused partially by the unwillingness of the residents to actively maintain and repair the dikes. A well-known tidal flood was the All Saints' Flood of 1570. It is known that 2892 people drowned in Friesland, although estimates (probably exaggerated) go up to 20,000 victims. The water reached heights up to 3.85 meters above NAP, flooding almost all of Friesland. Because the salty water did not flow away immediately, the ground became salty and the subsequent harvests were ruined. After the Christmas Flood of 1717, the dikes were raised and the individual dike responsibility was done away to be replaced by a municipal responsibility. The next major flood happened again in 1825. The necessity to reinforce and raise the dikes was obvious. After eleven years of labor, the sea dikes were brought to a relatively safe height by 1888, so that no serious flooding took place in Friesland during the water emergency of 1953. Presently, all of the sea dikes in the entire country have been raised to delta height.

Source: de Vleet, Ecomare