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 During times of plentiful water (i.e. rainy periods), extra water can be withdrawn from a river (or other source) and then injected and stored within an aquifer in a designated area.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.