Availability of fresh groundwater, salinisation

Description

The availability of fresh groundwater and surface water is important for agriculture, industry, drinking water and nature. Saltification of groundwater and surface water takes place in the coastal area of the Netherlands by intrusion of seawater via the large rivers and salt seepage (the flow of salt groundwater up to the surface). It is expected that the predicted climate change and future sea level rise will increase salt seepage and salt intrusion from the sea and reduce the availability of fresh groundwater and surface water. This factsheet deals with the availability of fresh groundwater. Groundwater The current availability of fresh groundwater in the Dutch coastal area is limited by the shallow occurrence of salt groundwater. This salty groundwater is ‘old’ seawater that has been withdrawn from the subsoil during the Holocene floods of the sea. Since the construction of polders by humans, this salty groundwater flows back to the surface (salt seepage). Due to these processes, the spatial variation of the occurrence of fresh groundwater is large. In the southwestern delta, and the northern coastal areas, the salt groundwater is very shallow (< 5 m-mv) while in the west of the Netherlands the salt groundwater is found between 25 and 50 m-mv. Thick freshwater bubbles (up to 100 m) are found under the dunes and are used for drinking water. Below higher sandy creek ridges are freshwater bubbles of 5 to 25 m thickness from which agriculture extracts for irrigation. The map with the boundary of 1000 mg/l chloride indicates on a national scale to what depth fresh groundwater is found and thus gives a good indication where fresh groundwater is available. The map is based on a large number of measurements but the spatial variation is so large that the map is not suitable for use on a local scale. The fresh-broken groundwater interface does not vary much over time because flow processes in the subsurface are slow. However, when extracting fresh groundwater in coastal areas, deeper salt groundwater can be attracted in a short period of time if the abstraction rate is too large. This process is called saltwater convolution and limits freshwater availability. The figure below shows that salinisation of abstraction wells is a serious problem. Definitions: Chloride is a conservative substance that is relatively large compared to other substances and is the dominant representative of the salinity of water. Definitions of fresh, brackish and salt water are therefore based on chloride concentration. Class: Chloride concentration (mg Cl/l) Sweet: < 1000 Broke: 1000 – 3000 Salt: > 3000

Resources

Name Format Description Link
0 https://data.rivm.nl/data/ank/DANK008a_verzilting_grondwater.zip
0 https://data.rivm.nl/geo/ank/wms?request=GetCapabilities

Tags

  • grondwater
  • landbouw
  • watervoorziening
  • beregening

Topics

  • TECH

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