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Adaptation option

Adaptation of groundwater management (2015)

Sea level rise, just like overexploitation of coastal aquifers, increases the chance of saltwater intrusion in groundwater bodies, particularly in low-lying areas. In general, reduced precipitations and increased water needs put groundwater resources at risk. A way of mitigating this threat is by systematically maintaining higher water table levels for groundwater, thus reducing the hydrological gradient from seawater. The Netherlands is at present evaluating this management option. Additional benefits that have been identified associated with the implementation of this measure are the reduction of soil compaction and peat oxidation and the reduction of water shortage in nature reserves. In arid and semi-arid regions, groundwater aquifers can be recharged in a controlled way so that excess water can be used later for water supply or environmental protection. Groundwater recharge is an indirect measure to increase the water supply within a managed water supply system. Contrary to rainwater harvesting which increases the water supply directly with additional water from natural precipitation, groundwater recharge feeds precipitated water into an aquifer in order to ensure and increase a continuous extraction of groundwater from this aquifer. The flow path of the percolating water together with mechanical and chemical filtering processes, and a considerable travelling and residence time, provides an effective filtering mechanism so that the extracted water generally has a high quality. Groundwater recharge does not face losses due to evaporation, as opposed to other methods that store water at the land surface, a particularly important feature in hot and dry climates. Water from groundwater recharge can be used, once extracted, in the same way as any other groundwater resource. The water used for recharging the aquifer can be taken from precipitation via reservoirs, but also from tertiary treated wastewater from water treatment plants.

No major infrastructure investments are required for groundwater recharge; however, the existence of a groundwater body is a pre-requisite, and there must be considerable open land surface area available to be irrigated in order for it to infiltrate into the soil and eventually, for the recharge of the groundwater. The chosen piece of land has to be in hydrologic connection to the aquifer (to be recharged) which requires some hydro-geological expertise. Groundwater recharge has the advantage of supporting a continuous groundwater flow along the natural flow paths, allows for an increased extraction of groundwater at already existing sites, maintains a higher groundwater level that serves agriculture as well as natural vegetation and ecosystem functions, and can prevent salty sea water intrusion at sites close to the sea.A less controlled, but more sustainable alternative to programmed groundwater recharge consists of green infrastructure measures which, inter-alia may contribute to improve natural groundwater recharge by reducing surface run-off if adequate connections exist between surfaces and aquifers. Solute transport of salt through porous media is a slow process, and in many low-lying areas, especially delta’s, the groundwater system is not yet in dynamic equilibrium through processes which were initiated in the past, like lake reclamations or peat excavation.It is difficult to make a distinction between climate change induced salinisation and autonomous/human induced salinisation in the evaluation of the performance of the adaptation measures.

Possible measures to reduce the vulnerability of groundwater systems to climate change are measures that will help to increase the recharge of the aquifer with freshwater or measures that reduce (the impact of) saline seepage on surface water and shallow groundwater. The following technical countermeasures are derived from literature:

  1. freshwater injection barriers through injection or (deep‐well) infiltration of fresh (purified sewage) water near the shoreline;
  2. extraction of saline and brackish groundwater;
  3. modifying pumping practice through reduction of withdrawal rates or adequate relocation of extraction wells;
  4. land reclamation and creating a foreland where a freshwater body may develop which could delay the inflow of saline groundwater;
  5. increase of (artificial) recharge in upland areas, for example by inundation of land, to enlarge the outflow of fresh groundwater through the coastal aquifer and to reduce the length of the salt water wedge;
  6. creation of physical barriers, such as sheet piles, clay trenches and injection of chemicals;
  7. climate compatible irrigation and drainage practices in agriculture in order to make efficient use of freshwater lenses in the root zone.

The dynamical behaviour of fresh water lenses is highly dependent on spatially variable geological factors and their reaction to climate change is still poorly understood.

Additional Details
Reference information

Adaptation Details

Category

Green

IPCC categories

Structural and physical: Ecosystem-based adaptation options, Structural and physical: Technological options

Stakeholder participation

Stakeholders involvement is a necessary practice, since the management of groundwater resources requires the active involvement of multiple actors, farmers in particular.

Success and Limiting Factors

Implementation of such measures may be hampered by: (i) their performance under local hydro geochemical conditions, (ii) their environmental impacts, and (iii) resistance within society. Risks connected to groundwater recharge are predominantly related to the recharge of treated wastewater. Here, a thorough and permanent quality control of the water to be infiltrated in the soil is required in order to avoid polluting the entire groundwater body permanently or for a long period of time. In the case of recharging surface water the risk of pollution is less severe; nevertheless, surface water also requires treatment before being infiltrated into the ground.

The EU Groundwater Directive (GWD), in conjunction to the Water Framework Directive (WFD) provide means to protect groundwater aquifers from pollution and deterioration. Amongst others, existing and new guidelines regarding the next generation of drainage basin management plans will be critically revised or drafted, taking into account climate change, and thus also include measures to reduce salt intrusion risks in coastal zones.

Implementation Time

5-25 years.

Life Time

More than 25 years.

Reference information

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Source:
ClimWatAdapt

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