Artificial recharge may be defined as augmenting the natural movement of surface water into underground formations by artificially changing natural conditions.
The application of artificial recharge techniques is commonly referred to as MAR (Managed Aquifer Recharge). There is a wide variety of MAR techniques for a range of applications on different scales (see box). In recent years there has been a rapid increase in MAR around the world. Publication of knowledge and experiences regarding MAR has progressed accordingly, but a sound global overview of applications, and access to information about individual MAR projects is still not available.
In 2002, the IAH-MAR Commission commenced a global MAR inventory which made little progress up-to-date. As a follow-up to this, the project 'Artificial Recharge of Groundwater in the World' has been implemented in 2006 by IGRAC and the Acacia Institute, in close cooperation with the IAH-MAR Commission and UNESCO-IHP. The aim of this project is to improve visibility, dissemination and reuse of information and knowledge related to MAR. Documentation on artificial recharge as it is currently applied in different parts of the world has been gathered in this project and made publicly available via this portal.
Provision of sufficient storage capacity under growing water demand and increasing climate variability is one of the main concerns for water managers in the coming decades. Accurate estimates for the required storage capacity do not exist, but it is expected that in 5 - 10 years from now additional storage capacity will be needed to provide sufficient water during dry periods.
Surface water storage in reservoirs behind dams represents the major part of the installed global storage capacity. However, the recognition of the environmental and social impacts, the growing concerns about dam safety issues and increased sedimentation has clearly demonstrated the limitations of large dams. In contrast to the large increase in dam capacity over last 50 years, there has been no significant increase in the controlled use of aquifers for subsurface water storage. Also it is not well known how much water is stored annually and what the potential capacity of subsurface storage is. Yet, a debate on the limitations of large dams would make more sense if there is a serious alternative to cope with the increase in storage capacity needed in the coming years to maintain even minimum supply levels to millions of people, both in rural and urban areas.
The expected intensification of groundwater use in coastal and deltaic regions leads to other points of concern. In the last half-century, population and economic growth have greatly increased fresh water demands. Coastal regions are important agricultural, industrial and tourism areas with high population densities. Unsustainable use of groundwater and surface water bodies leads to possible lowering groundwater tables, salt water intrusion and land subsidence. Climate change and associated sea level rise will only aggravate this issue.
Managed Aquifer Recharge might offer a mitigation measure to these issues. Controlled recharge and subsurface storage of water in aquifers, and recovery of this water in times when water is scarce, should be considered a serious alternative to large dams for maintaining water supply levels in the future. Recharge of aquifers can also alleviate the intrusion of salt water from the sea into coastal aquifers, and combat land subsidence caused by falling hydraulic heads due to overexploitation of aquifers. On a smaller scale, water harvesting techniques might catch water during rainfall events in order to recharge an aquifer, thus impeding the quick runoff out of a catchment area. This is particularly important for people living in (semi-) arid regions characterized by erratic rainfall and prolonged periods of drought, where every drop of water counts.