Kroon's Polders: how a dune warden made the island wider

An island that became too narrow

At the end of the nineteenth century, the western part of Vlieland was dangerously narrow. The North Sea was eating away at the dune ridge, and between the sea and the mudflats there was barely any sand left in some places. During a heavy storm, a breach was no theoretical risk.

Between 1898 and 1905, drift dykes were built, close against the existing Meeuwenduinen. Sand fences, marram grass, patience: the principle is simple, and it only works if someone keeps at it for years.

Jan Wouter Kroon

That someone was Jan Wouter Kroon (Vlieland 1874 – Zuidlaren 1957), dune warden and later overseer at Rijkswaterstaat. His idea went beyond reinforcing the dunes: by constructing new drift dykes on the southern side of the new dykes, he enclosed large, elongated stretches of beach. Between 1920 and 1925, four polders were created in this way. Until around 1935, work continued on the western side to protect smaller sand flats.

The polders were named after their creator. His older brother Symen did something similar on Terschelling during the same period.

What failed

Kroon wanted agricultural land. That never came to pass: the soil remained too saline and too wet. Water was pumped out with a windmill, and a farmer from the Posthuys tried keeping livestock there for a time, but it never became viable. Later on, the air force had a landing strip for light propeller aircraft in the fourth polder.

Looked at that way, the project was a failure. Only, in the meantime, it delivered precisely what the island needed: the western side grew wider, and the risk of a breach smaller.

What succeeded

Since the 1960s, Staatsbosbeheer has managed the area for nature. Pumping has stopped; culverts and weirs have been removed. In winter, large parts are submerged; in summer, they mostly dry out. In 1996, the sea dyke of the third polder was breached and an opening made between the third and the fourth, allowing salt water from the Waddenzee to flow in at high tide.

The result is a series of brackish pools with a salinity gradient: the first and second polders receive plenty of fresh seepage, while the third and fourth are saltier. Plants that are rare elsewhere grow across this transition. Over sixty bird species breed here, including the eider, spoonbill, avocet and cormorant. In winter, large flocks of geese gather here.

Watching without disturbing

The polders are fragile, and parts are closed during the breeding season. From the cycle path and from the dune ridge along the southern edge, you have a view across the water; a pair of binoculars does more here than a walk. The signs posted by Staatsbosbeheer set out the local access rules.

What you see is not untouched primeval nature. It is a failed polder that was given a hundred years.