Managing the invisible: Groundwater salinity in coastal areas

Written by Tibor Stigter, on 6 September 2018

Around 40% of the world’s population lives within 100 km of the coastline. With the numbers increasing rapidly, the pressure on coastal freshwater resources, especially groundwater, is huge. The out-of-sight nature of this resource makes it, paradoxically, susceptible to both over- and under-utilization.

This article is written by Ashwini Petchiappan, Communication Office intern, summer 2018

Underground reservoirs or aquifers are the largest available reservoirs of liquid freshwater, holding close to 90% of the world’s stock. This makes them a valuable, and often under-appreciated, resource in water-scarce regions. On the other hand, populous regions often make indiscriminate unplanned use of the resource, making it, among others, prone to escalations in salinity levels.

The aquifer in coastal areas is linked to the sea; an extraction of water from the reservoir is partly balanced by an influx of saline water from the sea, particularly when there is less rainfall. Some coastal regions have saltwater trapped in the subsurface sediments from floods in the past, when sea levels were higher. Groundwater abstraction at large volumes or at high rates can, therefore, cause a gradual increase in the salt content of the water, due to the higher influx of (trapped) sea-water, often making the water unsuitable for drinking or agricultural use. Considering the populations reliant on the resource, there can be significant consequences. 

In the Mekong Delta for instance, groundwater salinity affects an area that yields over 50% of Vietnam’s food production. In large coastal cities such as Maputo in Mozambique, more than 60% of the two million inhabitants have limited or no access to freshwater, and are increasingly suffering from high salinity levels. Climate change can further aggravate the problem of saline intrusion through droughts and sea level rise. Effective management of groundwater as a resource is, therefore, critical for the Sustainable Development Goals of ensuring food security and access to water in these regions.

Mitigating groundwater SALINity impacts for imPROVEd water security

The project SALINPROVE aims to address this problem in coastal areas of three different settings: Peri-urban Great Maputo (Mozambique), the Tra Vinh province in the Mekong Delta (Vietnam), and Laizhou Bay (China). The aim is to work together with the main users and stakeholders towards defining the different dimensions and impacts of the groundwater salinization problems, and develop feasible solutions, both for the present as well as under future climate and socio-economic changes. 

The research will help answer questions such as how saltwater intrusion occurs in the study areas, and how it is exacerbated by human activities and climate change. Attention is paid to the uncertainties involved, and to the differences between the regions. The project hopes to establish the socio-economic impacts of groundwater salinization. A key objective will be to develop technically and economically feasible mitigation or adaptation measures to the salinity impacts in each area, and to see how they promote inclusivity. The overarching goal is to implement informed decision-making for groundwater resources management.

Methods and strategies

Surface water flows quickly, and is recharged quickly. Underground water, however, is a slow system, operating on a timescale of decades to hundreds and even thousands of years. This makes monitoring of groundwater levels and quality essential - an aspect where regional partners play a vital role.

Tibor Stigter, Senior Lecturer in Hydrogeology and Groundwater Resources at IHE Delft, and Project Manager of SALINPROVE, outlines how this is done, “We jointly optimize monitoring systems, also integrating citizen observatories for early warning of salinity increase. We co-construct models that simulate groundwater dynamics and changing salinities, under different scenarios. And we co-design solutions such as increasing natural aquifer recharge by adapting land use, or reducing surface runoff. We ultimately test these measures for social, economic and technical viability, based on cost-benefit analysis, social surveys and interviews, as well as groundwater models.” 
By doing so, the adoption of these solutions by the relevant water actors is facilitated. The solutions could be mitigation measures, such as optimized pumping practices and locations, or adaptation measures such as the use of brackish water for salt-tolerant crops. The eventual goal is to allow management of groundwater in coastal areas to be based on factual information, and with a common objective: keep groundwater fresh and make it accessible to all. The methodology used in the project can be applied to different regions of the world, although the mitigation and adaptation strategies adopted would vary. 

Synergies: Working with partners and stakeholders

Tibor Stigter considers the novelty of the project to be the fact that stakeholders are involved from the start; they can contribute both in terms of knowledge and logistics.

Dr Dao Hong Hai, project representative from Ho Chi Minh City University of Technology (HCMUT), finds his university a convenient point of contact for the project in the Tra Vinh province of Vietnam. “We have a close relationship with the governments of the provinces in the south of Vietnam. With that relationship, the governments and departments of the provinces are willing to cooperate and provide support to us in many ways, especially through research, to ensure the sustainable development of the locality.”

The project has already spurred the interest of the local residents in the province of Tra Vinh to contribute, and help with the monitoring. Measurements for water level and salinity are done using simple and inexpensive devices through collaborations, such as with the Youth Union of Tra Vinh Province. Dr Bui Tran Vuong, Deputy Director General of the Division of Water Resources Planning and Investigation for the South of Vietnam (DWRPIS), strongly feels that it is helping create awareness about the issue, and makes people think of ways to use groundwater sustainably. “With the help of experts from IHE Delft, we have learnt to carry out the research step-by-step. We now know the location and distribution of the aquifers in the region. We want to develop practical ways to help the residents know how much water can be abstracted without adverse effects, and perhaps some measures to cope with the saline water intrusion.”

In Maputo, Mozambique, the biggest positive has been the establishment of a monitoring network, explains Dr Dinis Juizo, faculty member at Eduardo Mondlane University, a partner institution. Private operators, who provide groundwater to homes not reached by the public water utility, have been trained by the university to take measurements. An important step was to create a knowledge base to get a comprehensive picture of the system. “We have done well in integrating the work done by other projects.”

The next steps

Climate change is projected to have a twofold effect on the groundwater issue in the study areas. A drier climate is expected, with more droughts, but also with longer and more intense dry and wet seasons. While extended dry spells can impact aquifer recharge, continuous heavy runoff might be lost unless the storage capacity is improved. The need for adaptation is evident.

As the project has passed its halfway stage, the research has already dealt with the monitoring, climate scenarios and modelling aspects, and socio-economic surveys. The ensuing step would be to develop region-wise adaptation strategies. From 27 to 31 August 2018, a training workshop on “Adaptation and mitigation strategies to cope with saltwater intrusion in groundwater in coastal areas” has taken place in Tianjin, China, where partners from all four countries (China, Vietnam, Mozambique and the Netherlands) came together to discuss the issue, as well as the progress made in the project, and plans for the next year. Subsequent workshops organized by the local partners, and targeting key stakeholders, are scheduled to be held in each of the three countries where the project is being implemented.

The partners agree that it is often a challenge to get all stakeholders aligned in their views. However, it is important to get people involved throughout the process to keep the work going long into the future. Dr Bui Tran Vuong hopes to convince people in Tra Vinh to continue the monitoring activities even after the project ends. “People tend to react to what they see,” says Dr Dinis Juizo. What the project has managed is to bring awareness and visibility to this resource that had so far been largely invisible. This will be key to implementing informed decision-making for its effective management.

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