Grondwaterstroming in komgrond en de bepaling van enige hydrologische grootheden in verband met het ontwateringssysteem
1960
Hoorn, van, J.W.
The basin clay soil occupying an extensive area between the great rivers in the Netherlands is characterized by a profile with a highly permeable surface layer (20 cm) over a poorly permeable second layer (50 cm, K = 0.05 metre/ day) and a highly permeable subsoil (KD) = 1 metre 2/day). In this profile, a deep discharge in vertical direction through the second layer and in horizontal direction through the subsoil takes place. A shallow discharge in horizontal direction may occur, through the surface layer. There is surface run-off under special conditions.The occurrence of shallow discharge is determined by the relation between precipitation rate and infiltration capacity of the second layer. When the watertable remains below the top of this second layer, infiltration occurs in unsaturated soil, since infiltration capacity exceeds or practically equals the hydraulic conductivity of the second layer. But when the watertable reaches the top of the second layer, infiltration capacity becomes equal to the discharge rate of the drainage system in the highly permeable subsoil. The lower the initial watertable in the subsoil at the start of a rainy period, the longer the rain has to infiltrate into an unsaturated soil.Good drainage can be achieved under the rainfall of the Netherlands with an adequate system of ditches and tile lines only if in the highly permeable subsoil, so reducing radial resistance. Otherwise trench drains must be used.
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