Mekong Forum Homepage
Cao Vån H· Ph.D.
DIŒN ÐÀN MEKONG
by Cao Vån H·, Ph.D 2/1998
KEY ISSUES FOR MEKONG BASIN DEVELOPMENT PLAN (BDP)
Let start with some thoughts of good will and positive thinking.
In lieu of
MRC has been perceived as an agency set up to promote the construction of controversial dams and
water diversion of the Mekong and its tributaries. MRC has expressed support for a run-of-river plan
for large-scale hydropower developments.
- Positive thinking: MRC serves as a channel for regional action in the Mekong basin to foster more
integrative and sensitive approaches to Mekong resource management and development.
China and Burma’s non-membership hampers the role of the MRC. China in particular is a
significant player as the country that contains half the length of the river and 16 per cent of its flow.
China has unilaterally built the first mainstream dam and others are under construction or being
planned. China has least to gain from Mekong Basin cooperation, both as the upstream country and as
the dominant power in the region.
- Positive thinking: A truly Basin-wide program needs to take account particularly of China’s key role
in Basin resource management.
Significant flow alteration by upstream diversion and large hydropower dams would affect the Delta.
The new MRC Agreement with the other Lower Basin countries has removed veto rights for intra basin
projects during the wet season. . A significant change from the Committee rules is that downstream
countries no longer have an effective veto on upstream developments. Rules are structured around
notification and consultation on projects that affect dry season and wet season water flows. This was a
point, which contributed to Vietnam’s reluctance to sign the agreement when it was first proposed in
1992. Only 36 per cent of Thailand’s territory are in the Basin, but Thailand is nevertheless a
significant player. In part this is due to potential use of Mekong water on its own territory, with two
major diversion schemes planned that could affect downstream flows
- Positive thinking: Thailand will refrain from carrying out the inter-basin diversion scheme from the
Thai Kok and Ing tributaries to the Chaophraya basin
The planning tool to be used by the MRC is the Basin Development Plan (BDP) which is defined in
Chapter II of the Agreement as the "general planning tool and process that the Joint Committee would
use as a blueprint to identify, categorize and prioritize the projects and programs to seek assistance for
and to implement the plan at the basin level".
- Positive thinking: The goals of the BDP include bringing environmental and social issues into the
assessment of MRC actions.
Recognizing that the Mekong BDP is not the only initiative exists in the basin, the BDP must be drawn
in coordination with the ADB-sponsored Greater Mekong Subregion (GMS) initiative, initiated in 1992.
There are approximately 100 competing projects identified under the GMS program for infrastructure
development --transport, energy, and telecommunication-- and environment and human resources
related projects, but, as a whole, they do not exhaust the water resources development/management of
the Mekong basin including the Delta. Riparian countries cannot be content solely with these feasible
projects as they are sponsored by ADB or potentially financed by ADB. The Mekong BDP centers on
seven water-related activities:
- Forestry/Watershed management
- Hydropower (Energy)
- Navigation and Transport
- Tourism and Recreation,
- Urbanization and Industrialization
These water-related activity programs are to be developed under two cross-sectional themes of
environmental/ecological balance and human resource development. On Delta perspectives and
context, the strategic focuses and development roadmap can be structured within the BDP framework
and suggested on several prongs as detailed in this paper:
Salinity and acidity management in the Mekong Delta
The availability of freshwater which is central to salinity and acidity management
Watershed management is an issue at basin-wide level, therefore BDP should address all factors and
options related to upstream/downstream water sharing
Last but not least, poverty reduction and restructuring the Delta's economic base must be treated as
integrated elements of the BDP.
- Approach to Mekong Resource Development Within Vietnam’s Economic Framework
1.1. The Mekong Basin in Vietnam
Vietnam is the last downstream nation of the Mekong Basin. Within Vietnam, the Basin covers 29% or
approximately 96,000 square kilometers of the nation’s total area and is represented by two disparate
regions, the Mekong Delta and the Central Highlands, excluding a relatively small area in Dien Bien
(1,392 km2), upstream of Nam Ou, part of Nam Rom sub-basin.
The Mekong Delta spans 39,500 square kilometers (12% of country total). Its vast deltaic plains is
formed by sedimentation and erosion. The Delta has been constructed over time by overbank flooding
and sediment drifting southwest along the coast from the Tien and Bassac nine-channel mouths.
Monsoon rains from late May and peak in September and October, in combination with floodwaters
from the Mekong, cause annual flood and inundation in about 1.2 to 1.4 million ha from two to six
months. Discharge of the lower Mekong during the wet season averages of 39,000 m3/sec. In contrast,
in the dry season, low water discharge is 1,700 m3/sec. In the ebb season during February-May period,
salinity is most severe, as river flow is inadequate to prevent seawater intrusion.
The Mekong Delta is crucial to Vietnam as its "rice bowl", the richest agricultural area in the country.
It accounts for half the rice production, 40% of total agricultural output, and 27 percent of Gross
Domestic Product. Increased agricultural production has fuelled the economic liberalization or "doi
moi" since the mid 1980s and the Mekong Delta has been instrumental in this continuing process. The
Mekong Delta provides a home for slightly over 15 million people (22% of country total), making it the
second most densely populated region in Vietnam.
The Central Highlands cover the upstream areas of two Mekong tributaries, Se San and Sre Pok rivers.
The Se San river originates from the Ngo Clinh Mountains and is the largest eastern tributary of the
Mekong. This part of the Basin is typified by steep topography, has large hydropower potential and
forestry resources. The monsoon rains in the area last from June to October and the run-off in the wet
season accounts for approximately 80 percent of the yearly volume. The Central Highlands are
relatively underdeveloped, has the lowest population density in the country with about 3 million
people (4% of country total) living in an area of 56,000 square kilometers (17% of country total). It is
the home of many ethnic minorities. In recent years, this region has experienced high levels of
in-migration with the highest population growth rate in the country of 5.8%. The central Highlands are
important for upland agriculture especially for cash crops such as coffee and tea, and hydropower
potential. The second largest dam in Vietnam, the 700 MW Yali Falls Dam is under construction since
1994 and will be completed before the end of the century There are many on-going projects supported
by MRC for this part of the basin: the 66 MW Vinh Son dam, the 120 MW Pleikrong dam, the Ea Soup
multipurpose project and the Upper Sre Pok basin development plan.
In a capsule, the two regions comprising the Mekong Basin in Vietnam are characterized distinctly by
its unique population composition, ethnicity, income levels and other socio-economic factors,
topology, and ecosystems. They underscore approaches to natural resources development in Vietnam,
a sustainable development with broader concerns for environment. Rapid and sustainable
development of the Mekong Delta is central to Vietnam’s sustained growth.
1.2. Key Concerns: Salinity and Acidity Management
For Vietnam, key concerns are reduced flows of water from the Mekong River during the dry season
and increased flooding during the wet season. Recent increased flooding has been attributed to
upstream deforestation. Nevertheless, the yearly overbank flooding is a disguised blessing to the Delta
because flooding is helpful to flush the acid soils, to deposit fertile sediment into the floodplains, and
to bring nutrients to inland fisheries. As far as hydrological constraints to agricultural possibilities in
the Delta, a depth of prolong flooding of 60 cm is the threshold for rice cultivation-- too deep for any
varieties of rice, or any upland crops such as pineapples or sugarcane—impractical to construct too
high raised beds.
Above all, reduced flows of water during the dry season are the biggest concern. Salinity intrusions are
closely linked to flow rates through the river system and any decrease in flow will cause extensive
problems for agriculture and human habitations. The problems posed by acid sulphate soils, which are
common in the Delta, are also exacerbated by reduced flows. In other words, the Delta is facing
reduced source of water availability to alleviate two major soil constraints, namely soil salinity and soil
Salinity problems arise in the Delta, as the tidal effects throughout large areas of the Delta. Salinity
intrusion occurs during the dry season from February to May as freshwater flows are reduced (Figure
2). This problem appears to be worsening, and upstream developments within Vietnam and in other
riparian countries could exacerbate the situation. Salinity penetration extends into branches of the
Mekong ten to forty miles. About 1.6 million hectares of the Mekong Delta are affected by saline
intrusions during the dry season. Salinity penetration is more extensive in the smaller tributaries and
canals compared to the Tien and Bassac Rivers. The maximum salinity reaches 4.0 p.p.t around April.
Even worse, salinity intrusion makes the irrigation water in the canals become saline, i.e.; fertile soils
cannot be used for agriculture due to lack of freshwater.
Along the South China Sea, there are coastal areas of Long An, Ben Tre, Hau Giang and Minh Hai
provinces, which are permanently saline because they are inundated by seawater more than 9 months
of the year. The tidal floodplain covers an area of 216,000 ha (5.5% of the Delta. Salty soils are found
along the coast from Genh Hao (Minh Hai Province) to Go Cong (Tien Giang Province), Can Duoc and
Can Giuoc (Long An Province). They cover an area of 809.000 ha (21% of the Delta).
Figure 1.1: Salinity intrusion in the Mekong Delta
Acid sulphate soils
Nearly half of the Mekong Delta is susceptible to potential problems of acid sulphate soils (ASS). ASS
are those areas where the oxidation of pyrite (iron sulphide) and acidification process take place. .
Pyrite is usually found in tidal swamps, but it does not become a problem so long as the soil remains
inundated. Acid sulphate is formed when pyrite-rich sediments are exposed to oxygen. ASS have low
pH values and high concentration of aluminum, iron, sulphate, and hydrogen sulfide. The depth of
the sulfuric horizon (pH below 3.5) is used to characterize the soil acidity: severely acid soil where the
scale is within the upper 50 cm; moderately acid soil where the scale is between 50 and 80 cm, and
slightly acid soil where the scale is between 80 and 120 cm. Drained ASS produce sulfuric acid, which
dilutes into surface water, brings down the soil pH to below 4, attacks clay content of soils,
subsequently release aluminum, which is toxic to plant growth. The capillary process makes severely
acid soils unsuitable for agriculture.
Potential and actual acid sulphate soils are pre sent in many parts of the Mekong Delta covering a total
area of 1,590,000 ha, mainly in the Dong Thap Muoi and Long Xuyen Quadrangle. Acid sulphate soils in
the Delta can be subdivided as follows:
- Sulphate: found in the Dong Thap Muoi and Long Xuyen quadrangle, in low-lying areas along the
Hau River and in parts of the lowlands between the Tien and Hau rivers. This covers an area of 510,000
ha (13% of the Delta). These soils have very high concentration of sulphates and low pH values ranging
from 2.26 to 3.54. Dong Thap Muoi closed floodplain system affected by deep and prolonged
inundation during the rainy season covers an area of 414,400 ha (10.6% of the Delta) with high
concentration of sulphates.
- Salty sulphate: found in Ca Mau and along the shores of the Gulf of Thailand. This subtype covers an
area of 1,080,200 ha (28% of the Delta). Ha Tien open floodplain system is a relatively well-drained area
of 217,500 ha (5.6% of the Delta). Insufficient fresh water during the dry season and presence of salt
and sulphates in the soil make the area marginal for agricultural use. The U Minh Melaleuca forests of
peat and sulphate soil types cover an area of 189,400 ha (4.9% of the Delta).
Figure 1.2: Acid soils in the Mekong Delta
Basin Development Plan (BDP) Must Embrace Programs to Support Salinity and Acidity
Management in the Delta
It is crystal clear that salinity and acidity management are vital issues facing the Delta. They must be
incorporated into the BDP. It boils down to one single factor that adequate fresh water availability in
the dry season will help to solve or alleviate these two issues.
The salinity control measures and other resource developments in the Delta are set out in the Master
Plan for the Mekong Delta (NEDECO 1993). Salinity control measures involving the construction of
dykes and canals focus on these smaller watercourses and affect very large areas.
Acidity management is critical to the Mekong Delta as population pressures and programs for
agricultural expansion add to intense conversion of acid sulphate soils, mainly for rice production.
Dong Thap Muoi or the Plain of Reeds has transformed with new settlement and extensive reclamation. Farmers'
experiences in cultivation practices applied to acid sulphate soils produced encouraging results. Dong
Thap's rice production amounted to 2.1 million tons in 1994, compared with 600,000 tons in 1980. The
government of Vietnam targets to reclaim 101,000 hectares by the year 2010, out of the remainder
120,000 hectares still uncultivated.
Here lays the difference in approach to manage ASS entailed in this paper. As a proposal elsewhere in
this paper points to the conversion of deep ASS area into multi-purpose reservoir to provide
freshwater in the dry season, instead. Extensive rely on leaching ASS would lead to environmental
degradation. Draining of such soils resulting in exposure of severe acid sulphate soils, however, creates
major problems for Dong Thap itself and for downstream areas especially at the beginning of the rainy
season as acidic water is flushed down towards the sea. The resulting acidity transfers to surrounding
land, contaminates surface water and becomes a threat to aquatic ecosystems.
Summarily, management of potential or actual ASS should involve both precautionary action and
curative or adaptive interventions where acidity has become a problem. In this regard BDP for the
Delta must stress on an integrated management approach. BDP must strike a balance between ASS
treatment and environmental protection.
Furthermore, BDP for the Delta must find ways to effectively deal with acid sulfate soils with cursory
research on alternative interdisciplinary approaches including the anaerobic treatment process and
sulfate burying such as creating multi-purpose large-scale water reservoirs in the Delta's Dong Thap
and Long Xuyen Quadrangle to entrap silt buildup and provide source of freshwater in the dry season.
The hard fact is as long as freshwater is available for cultivation, almost any types of ASS are
manageable for rice cultivation or other upland-type-crops planted on raised beds.
About the author: Ho Van Cao obtained his doctoral degree in Economics from Georgetown University, USA.
He was a former Assistant Minister of Finance and Government Commissioner of Industrial
Development Bank of South Vietnam. He was a member of the National Petroleum Board and
Presidential Cultural and Social Commission. Notably, he was an Administrative Chief
of a district peripheral to Dong Thap Muoi (Plain of Reeds), worked and lived with
the Mekong delta people whose bare heels tarred with "phen" (sulphate soils). One of his pen name
is NGUON PHIEN (Pure Sulphate Nodule). In spite of his pen name he is an advocate
of any solution to solve the ASS (Acid Sulphate Soils) problems and hopefully to grow high-yield rice on it, knowing that the current combination of century-old farming methods with recent scientific researches on ASS are the only applications that one could be content with. But his relentless motivation coupled with his professional obsession still drives him toward miraculous solutions of the ASS-related problems.
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