BGR Bundesanstalt für Geowissenschaften und Rohstoffe

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TC Vietnam: Improving Groundwater Protection in the Mekong Delta

Report of the project:

Map of the Mekong Delta with the pilot provinces Sóc Trăng and Cà MauMap of the Mekong Delta with the pilot provinces Sóc Trăng and Cà Mau

Background:
The Mekong Delta has an area of 39,000 km² and a population of 17.5 million, 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, Sông Hậu (Bassac, right branch) and Sông Tiền (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 for flooding. The influence of tides reaches far inland.

Since the Miocene several transgression cycles deposited a series of unconsolidated sediments, which is up to 700 m thick in the centre, and forms a sequence of up to eight aquifers and aquitards, which thins out towards the sides of the delta. Thicknesses vary, and the aquitards are not always continuous, leading to hydraulic connections between aquifers. Large amounts of groundwater are saline, even further inland, so salinization cannot only be explained by recent seawater intrusion, but by syngenetic origin and by the strong sea-level variations during the Pleistocene.

Project approach for improving groundwater managementProject approach for improving groundwater management

Due to the high water demand of population and agriculture, groundwater is intensively exploited, especially in areas far from the river branches and close to the coast, where surface water often cannot be used. The groundwater monitoring wells in the urban centres show a decline of 5 - 10 m, sometimes up to 20 m, in the last 20 years. This leads to lowering of the land surface (subsidence) and intrusion of saltwater in the exploited aquifers. Because the monitoring network is not very dense and focussed on the Provinces’ capitals, it is difficult to assess the situation in the rural areas.

One task of the "Improvement of Groundwater Protection in Vietnam (IGPVN)" project is to improve the hydrogeological information, in order to better understand saltwater intrusion processes. This forms the basis for improved groundwater management and protection.

The project intends to further the development of a coherent national policy for groundwater protection, to acquire better data on groundwater, and to support the inter-provincial coordination of groundwater management in the Mekong Delta provinces.

Methods:
The project comprises several components: Technical Assistance, Policy Consultancy, Awareness Raising, and Capacity Building. While Policy Consultancy focuses mainly on the national level, the other components concentrate on the Mekong Delta.

Technical Assistance:
Together with the project partner National Center for Water Resources Planning and Investigation (NAWAPI), two of the southernmost provinces of Vietnam in the Mekong Delta have been selected as pilot provinces: Sóc Trăng (focus of project phase II, 2012 - 2014) and Cà Mau (focus of phase III, since 2015). Cà Mau is very susceptible to saltwater intrusion into surface water courses and subsequent water supply problems because of its large distance from the Mekong River and its long shoreline – the peninsula lies between the Vietnamese East Sea (South China Sea) and the Gulf of Thailand. Therefore groundwater is intensively used (by a total of approx. 138,000, mostly small, wells with an estimated total extraction of 373,000 m³/d) and, accordingly, shows a strong decline of water levels (by 6 - 15 m between 1995 and 2009) and saltwater intrusion.

Overview of the aquifers and aquitards in the southwestern Mekong DeltaOverview of the aquifers and aquitards in the southwestern Mekong Delta

A major problem for sustainable groundwater resources management is the partially insufficient level of hydrogeological information. There is information on a regional scale, which is however not detailed enough to understand the groundwater system on a local scale. The project has selected U Minh as a first investigation focus where extensive investigations aim to increase the understanding of the hydrogeological system (structure, hydraulic properties, saltwater intrusion processes). In this way, the project contributes to create the basis for a numerical model, which makes scenario analyses for the improvement of groundwater management possible.

As a first step, the available data and information have been collected and critically assessed (baseline study), in order to identify deficits and design the hydrogeological investigations.

The project built a monitoring well group at the investigation site in U Minh district, where also soil samples for pedophysical and mineralogical analyses have been collected. The well group allows for pumping and tracer tests in the main aquifer while concurrently observing the neighbouring aquifers to assess potential hydraulic connections. Afterwards, the well group will be used for water sampling and measuring water levels (with data loggers).

Design sketch of the well group and tracer testDesign sketch of the well group and tracer test

After analysing all collected data, a conceptual model of this coastal hydrogeological system will be developed. In the following, a numerical model will be implemented, especially for the simulation of saltwater flow.

Policy Consultancy:
One task of the project partner NAWAPI in the national water management is the development of technical guidelines and specialist contributions to Circulars (subordinate legislation) of the superordinate Ministry of Natural Resources and Environment (MONRE). Here the project supports NAWAPI with expertise and advice, especially regarding the international state of the art. The focus is on developing technical guidelines on groundwater protection topics in urban areas.

The Departments of Mineral Resources and Environment (DONREs) of the province governments in the Mekong Delta are supported in the development of guidebooks on implementing water legislation in groundwater management. Additionally, the results of the Technical Assistance component will be provided to the groundwater planning process in the pilot province Cà Mau.

Further Activities:
The hydrogeological investigations are complemented by capacity building activities (technical training for DONREs), by networking and experience exchange between provinces (“IWRM Round Table”), and by awareness raising activities (e.g. university students’ competition, teaching materials for schools).

Results:
Management recommendations for Sóc Trăng: Based on the extensive hydrogeological investigations in Phase II (evaluation of existing hydrogeological and water management data, construction of monitoring wells, time series analysis, assessment of water quality and isotope concentrations in surface and groundwater, groundwater dating with radio-isotopic methods), recommendations for the management and protection of groundwater bodies have been developed and further need for investigation identified. Many recommendations for groundwater use could be transferred to neighbouring coastal provinces.

Combined pumping and tracer test in U MinhCombined pumping and tracer test in U Minh

Baseline Study Cà Mau: The available data and reports have been compiled, if necessary digitised, and critically assessed. While there is quite extensive information on hydrogeological structure and groundwater use, groundwater level and quality data are sparse and the pumping tests insufficient. The usable data can be accessed from database and GIS.

Monitoring Well Group for Hydrogeological Investigations: On the outskirts of the town U Minh (Cà Mau province) a group of five monitoring wells was constructed in July/August 2016. Borehole logs and geophysical downhole logging are already available. The undisturbed and disturbed soil samples are currently analysed. Also, a step pumping test for determination of the well characteristics and as an orienting investigation has been performed. The tracer test was carried out in December 2016, the data is currently analysed.

Partner:

Literature:


Contact 1:

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

Contact 2:

    
Dr. Georg Houben
Phone: +49-(0)511-643-2373
homepage: www.bgr.bund.de/houben

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