Researchers have discovered why faults in the Brabant subsurface block water flow. An extensive study at the Peelrand fault near Uden shows that small sediment particles accumulate along fault surfaces, blocking groundwater flow, with implications for nature restoration, rainwater buffering, and drinking water extraction.
Faults as obstacles to groundwater
The subsurface of Brabant is characterised by numerous faults. These faults often form a natural barrier to groundwater flow. ''To understand why some fractures have such poor water permeability, a twenty-five-metre-long and two-and-a-half-metre-deep trench was dug across the Peelrand fracture near Uden. In that trench, we examined the soil layers along the fault and took samples. Permeability, grain size and microscopic properties of the sediments were then measured in the laboratories,'' Earth scientist Rimbaud Lapperre explains.
New mechanism discovered
The research by VU Amsterdam Earth scientists Lapperre, Cornelis Kasse and Ronald van Balen and WUR researcher Victor Bense showed that poor permeability is not due to a single cause, but to a combination of factors. Crucial is the movement of small sediment particles, such as clay, silt and fine sand, within a matrix of coarser sand. These particles accumulate along the fault plane and block the flow of water, a mechanism that has not been described before.
Implications for nature and water management
The findings have great practical value. For the province of North Brabant, the insight is important when restoring nature areas in and around the Peel, originally a peat swamp. Ronald van Balen; ''In the past, the water-retaining effect of faults was destroyed to enable agriculture. By restoring impermeability of faults, excess rainwater can be stored, which is of great importance in drier summers due to climate change.'' In addition, the management of surface water, drinking water extraction and geothermal energy can be better managed. The study also contributes to the ambition of municipalities and the province to recognise the Peel area as a Unesco Geopark.