Adaptation of groundwater management

Groundwater is an essential source of freshwater, accounting for about one third of the total world’s available water. However, groundwater resources are being rapidly used up at an alarming and unsustainable rate. Reduced precipitation and sea saltwater intrusion combined with groundwater over-exploitation are having direct impacts on aquifers recharge, discharge, storage and biogeochemical characteristics. Climate change and connected sea level rise are expected to further intensify these impacts, which however can be hardly quantified due to uncertainty in climate projections and the response of the local hydrological system to climate variability.

These circumstances call to reconcile human activities with the preservation and sustainable management of groundwater resources. In one hand it is important to improve the conservation of groundwater reservoirs, limiting water use and optimizing water reuse first. This shall be pursued through an integrated approach to water management also considering other sources of freshwater. Complementary to this, the availability of techniques meant to restore and even increase the natural infiltration capacity of freshwater into the aquifer is growing, including rainwater harvesting (collection and store of rainwater otherwise lost due to runoff) and use of pervious pavement.

These solutions alone might be not sufficient to recover aquifers experiencing intense pressure and over-exploitation. Other local solutions aiming to aquifer recharge can be therefore implemented to help coping with challenging problem associated with drought and water scarcity. During times of plentiful water (i.e. rainy periods), extra water can be withdrawn from a river (or other source) and then injected and stored within an aquifer in a designated area. In this way, water can be used to restore groundwater balance and later for water supply. Over the past two centuries, Managed Aquifer Recharge (MAR) was successfully implemented worldwide for various purposes: improve natural storage; water quality management; physical aquifer treatment; management of water distribution systems and ecological benefits. MAR is successfully used in Europe (e.g. Germany, Netherlands, France, Finland, Sweden, Spain, etc.), USA, South Africa, India, China, Australia and the Middle East. At the present, about 1200 case studies from over 50 countries have been implemented (MAR inventory portal).

The recharge of the aquifer can be achieved by either directly injecting surface waters into the groundwater system via wells, or indirectly by filling recharge basins that allow surface waters to slowly percolate downwards into the groundwater table below. Indirect recharge can be combined with measures aiming at improving the natural infiltration capacity as in the case of use of forested areas. Generally, indirect water infiltration techniques are well suited to unconfined aquifers, while direct injection techniques are more suited for deeper, confined aquifers. The most common types of MAR in Europe are induced bank filtration (direct method) and surface spreading methods (indirect method), located in central and northern countries where large perennial rivers and lakes exist. These systems are mostly designed for domestic end-use (drinking water supply), but recently they have also been considered to mitigate impacts of saltwater intrusion or to restore underground water balance compromised by over-abstraction.

Water for aquifer recharging can be taken also from tertiary wastewater treatment plants. Mechanical and chemical processes occurring when water percolate in the ground and the related considerable travelling and residence time are used as effective filtering mechanisms to ensure that water has the needed quality. Monitoring is anyhow required to assess the compliance with normative standards.

No major infrastructure investments are required for MAR. However, the existence of a groundwater body is a pre-requisite, and there must be considerable open land surface available to enable water infiltration into the soil and recharge of the groundwater. Such area must be in hydrologic connection to the aquifer to be recharged. 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 can serve different purposes (e.g. agriculture) and support ecosystem functions, and can prevent saltwater intrusion at sites close to the sea. Compared to other methods used to store water at the land surface, groundwater recharge enables to avoid losses due to evaporation, which is particularly relevant in hot and dry climates.

The main share of groundwater uses is devoted to agricultural purposes; therefore, farmers and landowners involvement is central for the management of groundwater resources and the implementation of related adaptation measures. Other important actors are drinkable water management companies.

Managed aquifer recharge can alleviate the impacts of climate change and the negative implications of dropping groundwater levels, e.g. due to overexploitation. Expected co-benefits compared to surface storage of water can play an important role in driving the successful implementation of MAR, as in the case of: strong minimization of evaporation losses, minimization of direct pollution and eutrophication, and relatively lower costs. However, the actual implementation of MAR measures may be hampered by:

• Their performance under specific local hydro, geochemical and hydrogeological conditions. MAR can be more efficiently applied in aquifers which can store large quantities of water and do not release it too quickly.
• Clogging (i.e. the accumulation of suspended solids from recharge water), which is the most widespread technical problem causing the reduction in hydraulic conductivity of the recharged structures.
• Lack of local data, enabling a detailed assessment of local conditions enabling the design and implementation of MAR techniques.
• Resistance within society and regulatory constraints. Landowners and administrations must recognize the economic importance, feasibility, risk and benefits of MAR and be involved since the design phase. Lack of a full engagement can bring to unacceptance. In some countries MAR needs a prior approval in compliance with environmental norms and environmental impact assessment has to be carried out.

The costs and benefits of MAR systems are often challenging to monetize, as they vary significantly depending on the specific type of recharging system used, performance objectives, local hydrological and physical conditions, planned uses of the recovered and stored water, and available alternative for water supply. The costs of MAR interventions include capital, operation and maintenance costs. The design of MAR should consider opportunity costs associated with land; i.e. revenues that could have been obtained if the property was sold or rented, or the value of goods and services that would have been obtained if the land was alternatively used.

The EU Groundwater Directive (GWD), in conjunction to the EU Water Framework Directive (WFD), provides means to protect groundwater aquifers from pollution and deterioration, recognizing MAR as a groundwater management tool supporting such aims. There are differences among established national legislations and a lack of a comprehensive legal framework dealing with MAR schemes.

Implementation time is highly site specific; it generally ranges from to 5 up to 30 years.

Lifetime depends on local conditions and management approaches.