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Jouke Velstra

Position: PhD student
Telephone: +31 182 687 117

Position: Scientific Researcher
Acacia Water Ltd
Jan van Beaumontstraat 1
2805 RN Gouda
The Netherlands

Behaviour of fresh water lenses on a parcel scale in relation to field drainage systems and the capillary flow under current and future climatic conditions

Supervisors and collaborators:

Duration: 2008 -
Funding: Research programme Living with Water, research programme Knowledge for Climate, Acacia Water

Research background

In many coastal and arid regions field drainage is applied to control groundwater levels but also salinities of groundwater and unsaturated zone. In coastal areas with upward seepage of groundwater, notably the Dutch polders, drainage systems intercept brackish groundwater and allow rainfall to form shallow fresh rainwater lenses. These lenses are crucial for sustaining crop growth. Likewise drainage systems in semi-arid regions restrain the groundwater from rising to close to the surface, where evapotranspiration would lead to salinization. In the past improper or lacking field drainage made extensive areas turn into saline wastelands, as the rising groundwater resulting from irrigation losses and deforestation was not curbed.
Design of field drainage systems are generally based on rules of thumb or, at best, on analytical models for saturated groundwater flow. However these underlying conceptual models do not include the intricacies of water and salt transport in the dynamic zone from the upper groundwater to the surface. The behaviour of the hydrological boundary layer is complex. 2D-resistivity soundings of croplands on clay soils displayed the presence of fresh water lenses between tile drains and upconing of brackish groundwater near the drains. The thicknesses of the lenses vary from of few decimeters to meters, have a strong seasonal pattern.
The objective of my study is to get more insight in the behaviour of fresh water lenses in relation to field drainage systems and the capillary flow. With respect to the latter particular attention is paid to incursion of brackish water into the root zone.