D. Parlevliet

De Rijnlandse ontginningen: op hoogveen of laagveen.

Historisch-geografisch tijdschrift 21 (2003) 60 - 68.

Een eeuw geleden werd nog algemeen aangenomen dat het middeleeuwse Holland voor een belangrijk deel bestond uit laagveen. In 1929 constateerde Polak echter dat de Hollandse venen in feite verdronken hoogvenen waren, wat bleek uit de dikke lagen veenmosveen die in boringen rond Amsterdam werden gevonden. Later bleek ook in een groot deel van midden Noord-Holland hoogveen voor te komen (Polak, 1929, p. 178; Pons & Wiggers, 1960, p. 31). Dat loste meteen de vraag op hoe die gebieden bij de ontginningen waren ontwaterd, want hoogveen kan in grote koepels meters boven het grondwater uitgroeien en is dus met sloten eenvoudig te ontwateren.

Bogs or fens in the area along the Old Rhine

From the 10th century the peat areas of Holland were reclaimed. It was supposed that these consisted of living raised bogs, which grew several meters above sea level. This explained why the ground water level could be lowered by digging ditches for crowing crops, even during centuries of shrinkage of the peat. When the land became eventually too wet it was dug for use as fuel. The present absence of moss peat was explained by the fact that only this peat could be used for turf in contrary to the woodpeat, which still remains alongside the rivers. In this article it is argued that in the area around the Old Rhine also wood peat was widely used as turf. Younger Sphagnum peat is also unsuitable for agricultural use while the amounts of the proposed fertilisation are too low. Wood peat can also grow above sea level, making it possible to lower the groundwater level. It is however not yet proved that it can grow high enough to accountfor the long time of shrinkage.