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TC Vietnam: Improving Groundwater Protection in the Mekong Delta

Report of the project:

Background:
The Mekong Delta has an area of about 39,000 km², is home to about 17.5 million people, and is a major agricultural region of Vietnam (mainly rice, but also fish, shrimp, vegetables). It is dominated by the two main branches of the Mekong, Hau River (Bassac, right branch) and Tien River (main branch), and by an extensive network of canals, that is used for irrigation and transport. The elevation of the land surface is generally only a few metres, making the area susceptible to flooding. The influence of tides reaches far inland.

The aquifers and aquitards in the southwestern Mekong DeltaThe aquifers and aquitards in the southwestern Mekong Delta Source: BGR

Since the Miocene, several transgression cycles deposited a series of unconsolidated sediments, which are up to 700 m thick in the centre, and forms a sequence of up to fourteen aquifers and aquitards. The sediments thin out towards the sides of the delta. Thicknesses vary, and the aquitards are not always continuous, leading to hydraulic connections between aquifers. The two topmost aquifers are saline over large areas but also lower aquifers show some saline areas, even further inland, so salinization cannot only be explained by recent seawater intrusion, but also results from a syngenetic origin (i. e. formed at the same time as the enclosing sediments) due to the strong sea-level variations during the Pleistocene.

Map of the Mekong Delta with the pilot provinces Ca Mau, Bac Lieu and Soc TrangMap of the Mekong Delta with the pilot provinces Ca Mau, Bac Lieu and Soc Trang Source: BGR

Due to the high water demand for domestic and agricultural use, groundwater is intensively exploited, especially in areas far from the river branches and close to the coast, where surface water is often too saline. In the last 25 years, the groundwater monitoring wells in the urban centres show a decline of 5 - 20 m, sometimes up to 30 m. This leads to additional lowering of the land surface (subsidence) and potential intrusion of saltwater into the exploited aquifers. Because the monitoring network is not very dense and focussed on the provincial capitals, it is difficult to assess the situation in the rural areas.

Together with the project partner, the National Center for Water Resources Planning and Investigation (NAWAPI), three of Vietnam's southernmost provinces in the Mekong Delta have now been selected as pilot areas: Soc Trang (focus of investigation in Phase II from 2012 - 2014), Ca Mau Province (mainly in Phase III since 2015) and Bac Lieu (since the end of 2020).

Based on four fields of action, central and local environmental authorities are being supported in the implementation of groundwater protection and management.

1) Strengthening provincial authorities in the implementation of regulatory requirements

Guidebooks and case studies: The Ministry of Natural Resources and Environment (MONRE) has issued some new regulations on groundwater management in recent years. However, implementation in the provinces at the Departments of Natural Resources and Environment (DONRE) is still in its infancy. The project "Improvement of Groundwater Protection in Vietnam (IGPVN)" has developed three guidebooks for local authorities, enterprises and well owners in Ca Mau Province and Bac Lieu Province and accompanied them with training. The project also developed an inventory of legal regulations on groundwater in Vietnam as a reference (Hanh, 2021).

The IGPVN Project has developed three groundwater management guidebooks for local authorities, enterprises and well owners in Ca Mau ProvinceThe project has developed three groundwater management guidebooks for local authorities, enterprises and well owners in Ca Mau Province Source: BGR

Feasibility study: A new regulation (Circular 24/2016/TT-BTNMT) requires that all production wells with a production rate of > 10 m³/day should designate a groundwater protection zone of at least 20 m around the well. The evaluation of the well cadastre (Hanh & Steinel, 2021) showed that in many cases, this is made difficult by nearby buildings, so viable solutions have to be found. The main focus should hence be on the protection of the well head and the IGPVN Project has established two demonstration models for this purpose.

Groundwater monitoring status: This study was conducted to (1) support the DONRE in developing a compelling groundwater monitoring outline that can be approved by the provincial government; (2) review the current legal regulations related to groundwater monitoring in provinces; (3) review the current status of groundwater monitoring in Ca Mau Province; and (4) give recommendations to improve groundwater monitoring in Ca Mau Province (Hanh & Steinel, 2021).

Demonstration model for wellhead protection: before (left) and after (right) with concrete construction, groundwater monitoring well, water supply pipe with extraction meter, fence, and information boardsDemonstration model for wellhead protection: before (left) and after (right) with concrete construction, groundwater monitoring well, water supply pipe with extraction meter, fence, information board about the well as well as information board about the groundwater protection zone Source: BGR

2) Collecting information on groundwater resources and developing monitoring networks

Result of tracer test with fluoresceinResult of tracer test with fluorescein Source: BGR

Monitoring wells for hydrogeological investigations: On the outskirts of U Minh City (Ca Mau Province), a group of five groundwater monitoring wells was constructed in July/August 2016. Water samples were collected, a step pumping test and a tracer test were carried out (Stöckl et al., 2017). The results (Pechstein et al., 2018) showed that leakage and hydraulic heterogeneity could play a significant role in groundwater flow behaviour and salinity distribution. Due to the groundwater age of more than 45,000 years, groundwater is considered as fossil and groundwater abstractions are thus unsustainable.

Georeferenced well inventory for licensed production wells in Ca Mau CityWell inventory for licensed production wells Source: BGR

Well inventory and database: A comprehensive survey of licensed production wells was carried out in Ca Mau Province in 2018/2019. The existing well licences were digitally recorded, assigned unique identification numbers, recorded in the field with a digital KoBo tool and, if possible, the water level and salinity were measured. The results were transferred to a customised database that allows both licences and monitoring data to be managed and visualised, thus also facilitating the allocation of new abstraction licences (Renck et al., 2021). The database was replicated in an updated version with more functionalities Bac Lieu Province and a training for the survey of production wells has equipped the DONRE with the knowledge to conduct their own well survey (Manh & Tham, 2021).

Telemetric groundwater level measurements: In the previous project phase III, several groundwater monitoring wells were constructed in Ca Mau (U Minh City) and Soc Trang provinces. These have now been equipped with telemetric data loggers, making it easier for the authorities to monitor groundwater levels and to transfer the data to local and national databases. In Bac Lieu, four research wells were rehabilitated and also equipped.

Map of total licenced abstractions by aquifer for each districtMap of total licenced abstractions Source: BGR & NAWAPI

Study on licensed groundwater abstractions: The knowledge of amount and location of groundwater abstractions is a vital component and a legal requirement for the management of groundwater resources in the Mekong Delta, where recharge of groundwater is thought to be limited. As groundwater abstractions are changing by the year and require regular updates, a static map or large tables representing the abstraction status at one point in time is not adequate for the groundwater management tasks. The IGPVN Project has developed a series of groundwater abstraction maps (Steinel & Seeger, 2021) based on the licensed abstractions from 2017 using virtual layers in QGIS. These maps can easily be updated with the latest abstraction data, which are released every 5 years.

Groundwater level contour map for the aquifer qp2-3 as of 30.04.2020Groundwater level contour map Source: BGR & NAWAPI

Study on groundwater levels depths and trends: Groundwater level (GWL) measurements are the most common parameter for hydrogeological interpretations. The IGPVN Project studied the long-term trends from 118 monitoring wells (Steinel & Post, 2021), produced GWL contour maps from 234 stations for April 2020 (Dersch & Steinel, 2021) and looked also at seasonal and daily trends for the IGPVN wells in U Minh, Ca Mau province (Hanh & Steinel, 2021). Groundwater abstractions have significantly altered the regional flow system and have induced lateral and vertical flows.

Trend of mean groundwater level over all monitoring wells in the Mekong Delta by aquiferGroundwater level over all monitoring wells Source: BGR

GWLs in the Mekong Delta have been declining for all aquifers except the topmost Holocene aquifer, whereby the lower (Pliocene and Miocene) aquifers show a faster declining rate (0.46-0.49 m/year) than the upper (Pleistocene) aquifers (0.16-0.33 m/year). Inter-annual variations in GWL correspond to wet and dry years, showing the increasing demand for groundwater in the drought years.

3D model for the Ca Mau Peninsula showing bore logs and virtual cross sections3D model showing bore logs and virtual cross sections Source: BGR

Overview of aquifers and aquitards in the southwestern Mekong Delta: A major problem for sustainable groundwater resource management is the partly insufficient level of hydrogeological knowledge. Information is available at the regional scale, but it is not detailed enough to adequately understand the groundwater system at the local level. For the Ca Mau Peninsula, existing reliable borehole profiles are evaluated, the layers are assigned to the 14 hydrogeological units and then interpolated. The resulting 3D model (Tam & Steinel, 2021) has several management functions. It was also used to investigate the relationship between land subsidence and thickness of the clay layers.

Intersection of IGPVN salinity maps for the aquifers qp2-3, qp1, n22 with 1.5 g/l total dissolved solids (TDS)Intersection of IGPVN salinity maps Source: BGR & NAWAPI

Salinity maps: Data from the well survey and from other investigations in the province of Ca Mau have been collected and were analysed to produce detailed salinity maps (Manh & Steinel, 2021) for the most important aquifers. Here, the 3D model played an important role in assigning the data to the aquifers. Results show that the heterogeneity of data is high, but some vertical and spatial patterns could be found.

Hydrogeochemical sampling campaign: A groundwater sampling campaign at 120 national monitoring wells was undertaken to investigate the hydrogeochemical characteristics and the age distribution to draw conclusions on hydrogeochemical processes, groundwater recharge, leakages between aquifers, and the origin of salinity (Steinel et al., 2021). A field protocol (Steinel, 2021) and on the job training was provided. All samples were analysed for major/minor ions and stable isotopes and 88 samples were dated using the radiocarbon method with Accelerator Mass Spectrometry (AMS). Hydrogeochemical modelling and interpretation of results is still ongoing.

3) Transfer of the findings into decision-making for water management planning and drinking water supply

Example of a scenario in the worksheetExample of a scenario in the worksheet Source: Schmidt, 2020

Groundwater regulation: Decree 167/2018/NĐ-CP aims to limit the use of groundwater to counteract falling groundwater levels, salinisation, land subsidence and groundwater pollution. However, the criteria for designating groundwater exploitation restriction zones are sometimes poorly defined or there is not enough data for them, making it difficult for local authorities to take all criteria into account. In cooperation with the ViWaT-Planning research project and with the help of interactive software, different scenarios for Soc Trang Province could be presented to assess the impact of the individual factors (Schmidt, 2020).

Land subsidence rates in the Mekong DeltaLand subsidence rates in the Mekong Delta Source: Neussner, 2019

Land subsidence: With progressive land subsidence of up to several cm per year and simultaneous sea-level rise, the low-lying Mekong Delta could be at risk of large-scale flooding. To better assess this situation, the IGPVN Project and the Gesellschaft für Internationale Zusammenarbeit (GIZ) have activated the EU Copernicus service in 2019 to produce the first delta-wide INSAR dataset (https://emergency.copernicus.eu/mapping/list-of-components/EMSN062). The dataset includes more than 750,000 points and time series from 2014 - 2019 and has already been used in several studies on land subsidence and its cause, such as groundwater abstraction, and disseminated to relevant stakeholders. Detailed maps have been produced for the provinces.

4) Awareness raising among groundwater users and decision-makers and networking between research and groundwater management stakeholders

Awareness raising has been closely interlinked with activities in the other fields of action. In the provinces, this is mainly achieved through trainings and involvement of technical and functional staff of partner and intermediary organisations. For example, in the well survey in Ca Mau more than 110 staff members of the Department of Natural Resources and Environment (DONRE), of sub-DONREs and of municipalities were involved. The development and dissemination of the guidebooks is carried out under the leadership of the DONREs.

Conferences such as the "Vietnam Water Week (VACI)" and the "Mekong Delta Conference" in June 2019 as well as technical workshops, e. g. on the groundwater information system (with MONRE) and on land subsidence (with GIZ) are used for horizontal and vertical dissemination of experiences and technical results in line agencies and provinces.


Partner: National Center for Water Resources Planning and Investigation (NAWAPI)

Project: Website "Improvement of Groundwater Protection in Vietnam (IGVPN)"


Literature:

Reports

Presentations


Contact 1:

    
Dr. Roland Bäumle
Phone: +49-(0)511-643-2394

Contact 2:

    
Dr. Anke Steinel
Phone: +84-24-36740494

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