2.1 billion people have no access to safe drinking water. One reason for this is the sinking of the water table due to over-exploitation of groundwater reserves. Water scarcity can have health, environmental and socio-economic impacts, and even lead to conflict.
It is becoming increasingly difficult to meet the fresh water needs of humans and ecosystems; particularly in coastal areas, as sinking groundwater levels lead to salt water intrusion. The salinisation of soils causes drinking water shortages and makes agriculture impossible, while flora and fauna are displaced. Last but not least, a lowering of the level of groundwater in coastal regions enables flooding and ultimately leads to people losing their livelihood and homes.
The solution to water scarcity comes from nature itself
Innovative new underground storage solutions for groundwater can help: Subsurface Water Solutions (SWS), developed by the Dutch KWR Watercycle Research Institute, combine various innovative methods for constructing and managing wells, which ensures that advanced groundwater management and maximum control of drinking water reserves is made possible.
Instead of artificial water tanks or cisterns, SWS use nature itself as storage method. This involves working with, and not against, nature: SWS not only enable continuous and sustainable freshwater supply in coastal areas, but also help to restore the natural flow of groundwater. This counteracts the negative effects of urban areas and increasing periods of drought, while areas once tainted by saline can be reclaimed by flora and fauna.
SWS were piloted and tested in the Netherlands. As part of the project "Improved water quality in coastal regions with sustainable aquifer storage- SUBSOL", adelphi is currently supporting the transfer of technology to Brazil, China, Mexico, Vietnam and Cyprus. In an interview, Project Leader Ronjon Chakrabarti talks about the potential of the new technology.
Saltwater intrusion in coastal areas often poses a massive threat to humans and the environment. What are the reasons for this?
Ronjon Chakrabarti: Coastal areas in particular are often densely populated and have active economies. The consequence of this is a strong abstraction of groundwater. Due to changing rainfall patterns and human activity, such as the straightening of watercourses and land sealing as a result of building and agricultural use, infiltration decreases; so less fresh water penetrates the soil than what is extracted. One particular case is the overuse of natural aquifers in semi-arid areas with rainy seasons, in which theoretically at least, enough water is available, and dry periods in which high amounts of groundwater are extracted. There is an additional dilemma in coastal areas: saltwater can enter aquifers through the lowering of freshwater levels - but as fresh water is lighter than salt water, no fresh water can further seep into the aquifer once it has been salinised. This means that over-used fresh water reserves cannot be refilled in a natural way, even in the rainy season.
How does SUBSOL counteract this?
Ronjon Chakrabarti: The SUBSOL solution for the underground storage of water (SWS) uses natural aquifers that have been salinised due to human overuse. Depending on the aquifer, vertical or horizontal wells are operated by an intelligent controller on multiple levels. Different technologies are used, the principle of which is similar across different cases: The wells are equipped with sensors that measure the water quality at the different well depths. If necessary, fresh water is then infiltrated (for example, through rainwater) or salt water is extracted.
"Salinised areas are being revitalized for flora and fauna"
In this way, SWS work with and also for nature: Natural aquifers are used for the production of drinking water, from which the ecosystem also benefits: Through regeneration of natural aquifers, salinised areas are once again revitalised for flora and fauna. SWS are therefore an environmentally friendly alternative to expensive underground tanks or surface reservoirs (which take up space) for supplying fresh water. In addition, SWS provide an efficient, cost-effective and sustainable alternative to energy-intensive desalination technologies such as reverse osmosis. On average, the supply of fresh water of the highest quality through SWS costs only half to a quarter of the price of water treated by reverse osmosis systems. The drinking water supply is thus made cheaper. This also secures the livelihoods of many people, as this cheaper alternative can make it worthwhile to once again farm in salinated areas.
What is adelphi's role in disseminating SWS?
Ronjon Chakrabarti: As part of our SUBSOL project, we use open source tools developed by our partners to perform simple feasibility studies on the application of the technologies. For their application, we carry out missions at various hotspots for saltwater intrusion around the world in order to collect data and compile information. We do this by presenting SWS on site, discussing it with local stakeholders, and developing concepts for local, specific application of the technology. In some cases, these concepts are further developed into concrete feasibility studies, pilot facilities, and project proposals.
Have there been any success stories? Where has SWS already been implemented?
Ronjon Chakrabarti: Initial studies in Recife, Brazil have shown promising results. In coastal urban areas, the water table has in recent decades dropped to 50m and has been penetrated by high amounts of saltwater. In the rainy season, as a result of the sealing of the city, the water flows through canals directly into the sea and is then lost. This water can be collected de-centrally from roofs and fed to an aquifer after a simple treatment. This solves several problems simultaneously: 1.) The saltwater intrusion is stopped. 2.) fresh water storage is created. 3.) the sinking of the water table is stopped, and 4.) flooding is reduced. With the use of SUBSOL tools, we calculated that there was sufficient rainwater and that the aquifer showed favourable conditions for storage. The effective use of SWS could cover the entire water supply of some parts of the city.
"SWS has the potential to ensure a regular water supply for all levels of the population"
As a result, we sent the aspiring technical environmentalist Anika Conrad of adelphi to support the construction of a first pilot system. The system is now being installed at a school that because of saltwater intrusion can no longer use its well. The SWS pilot system intends to remedy this by directing rainwater collected from the roof into a well after it has undergone a simple treatment. The school is located in one of the most densely populated areas of Recife, just 200 meters from the sea. The public water supply here is irregular, resulting in many private, often illegal, wells being built, which then leads to significant over usage of groundwater.
In principle, SWS in Recife has the potential to ensure a regular water supply for all levels of the population and many parts of the city. The city administration of Recife has also already shown interest in SWS and is currently identifying potential projects. For example, at a public covered marketplace, rainwater should be collected and purified via SWS. This will ensure water supply for the marketplace – of the estimated 7 million litres of water a year that are collected on the rooftop, only about 2.9 million litres are needed for the supply and cleaning of the market. Additional purified fresh water would come via an infiltration of the aquifer and thus benefit Recife's population. At the same time, the city's damaging effect on the ecosystem can be reduced in a cost-effective manner: the saltwater intrusion and the sinking of the water table are stopped and flooding is mitigated.
Further insights into the implementation of SWS can be found in this report.
Use of SWS in Mexico
In Mexico, adelphi and its project partner Arcadis have organized information events on SWS. In particular, the regions of Guadalupe and San Quintín in Baja California have also been affected by saltwater intrusion due to sinking groundwater levels. Here, possible applications of SWS have already been discussed with local stakeholders while solutions have been developed. More information can be found in this report.