Geoscience Reference
In-Depth Information
reinforcement of wooden piles, manufacture of concrete (= growing together) from
pozzolan sand with chalk from heated limestone. The Romans built their Coliseum
on an enormous concrete plate placed in a dug lake. They were also the best road
builders with 90 thousand km primary roads (viae consulares) and 200 thousand
km secondary roads (viae vicinales). Emperor Nero built a 40 m high stone
reservoir dam that resisted 13 centuries.
Since the last glacier the sea level rose and the landscape in the former
Netherlands underwent drastic changes. Also the groundwater levels rose and soils
were covered partly with peat. When the land temporarily drowned clay and sand
layers were deposited. Dunes took shape and permanent settlements of fishermen
occurred near eutrophic river mouths. Two thousand years ago, possibilities for
inhabitation improved and many small farming communities lived at the edges of
peat lands and along creeks in the inland. Such a fairway of that time was the
Gantel, which ran from the river Maes to the Old Rhine along Delft. The Romans
canalised the bedding so that navigation and trade could flourish.
The first millennium of our era
In the third century AD, due to wetting of the area, political instability (the
Romans had left) and epidemics (malaria), the Dutch population left to eastern and
southern sand soils. Excessive peat growth created a real morass in the western
part. Thereafter, land clearing and building were regulated and executed by
monasteries and by armies of serfs of kings and landlords. When desiccation rose
again, land developments increased by installation of dewatering systems,
stimulated by duke Dirk II, the largest landowner. Frisian emigrants were
encouraged to come to western Holland by offering a piece of land with tax duty
(tied farmers). At the end of the first millennium larger cities developed together
with professional communities (guilds) and farmers corporations.
Siphons were built to promote dewatering during low tides. In Valkenburg,
Schiedam-Kethel and Vlaardingen valve-sluices (see Fig 17.2a) are found dating
from the first century. A dam of clay and sods riveted by palisades provided water
retainment. Dikes were built to protect the plane lowlands against high river waters
(Fig 1.2). The peat lands were mined for turf (heating, cooking) and salt
production, and in 800 AD this caused a dramatic land loss. Our present-day lakes
and lowlands are mainly the result of human action.
4
the early 15
th
century ushered in the revival of the classical orders in Italian Renaissance
architecture.
4
When mining peat, the land was divided into long strokes with ditches at both sides that
dewatered to a larger channel (wetering), which ended in a creek. Villages arose as wisps at
the edges of the plots. By dewatering the land subsided sometimes meters under seal level.
Mounds and dikes were erected which caused the soft soil underneath to compact but also
covered the peat against oxidation. Subsidence and wetting made agriculture impossible.
The lands became pastures and meadows. Now, some areas are lovely nature reserves.
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