The groundwater shows high upward gradients in the direction towards the drainage channel.
It can be covered with up to 2 m of clayey silt or organic rich hydrous sediment while at some locations, the ditch cuts directly into the aquifer sands.
Because of its heterogeneity, the efficiency of the ditch varies strongly, resulting in even more complicated flow patterns .
Introduction Both tritium and helium isotopes have been used as environmental tracers of groundwater flow in a variety of hydrogeologic settings.
The He samples collected in 2001 and measured by the Bremen Mass Spectrometric Facility for the measurement of helium isotopes, neon, and tritium in water .
The thickness of the overlying alluvial or flood plain loam varies from 0.2 to 4.0 m.
The loam is clayey, sometimes sandy organic rich silt with strong variations in the hydraulic conductivity.
The potentiometric surface shows steep gradients directed to the polder centre.
During the first 500 m distance, the gradient decreases rapidly due to the pressure release from drainage.
Melioration activities included the redirection of the former riverbed further towards the east, the installation of an extensive drainage ditch and pumping station system and the building of a levee along the entire river.