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1 May 2005 Watershed Classification in the Lower Mekong Basin
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The environmental situation in the Lower Mekong Basin

The Lower Mekong Basin (LMB) arguably has one of the most diverse biotic and cultural landscapes in today's world. However, against the backdrop of residual impacts of the Indochina conflicts coupled with the extraordinary pace of economic development in some of the riparian countries over the last decade, contradictions between economic growth and environmental protection have become increasingly apparent. Fundamental political and economic changes in each country have had adverse environmental impacts on the region's shared resources. Seeking to replicate East Asian patterns of growth and industrialization, national leaders have pursued economic growth with minimal environmental considerations as a national aim. This has serious environmental consequences for the LMB, such as widespread deforestation, degradation, indiscriminate conversion of agricultural lands, changes in flow regime, pollution of water bodies, declining fish and wildlife populations, and generally decreasing biodiversity—to name only a few.

The Lower Mekong Basin on the Swiss research agenda

Based on these facts and on the existence of a well-established partner network involving, among others, the Asian Institute of Technology (AIT) and the Mekong River Commission Secretariat (MRCS), the Greater Mekong Subregion was integrated into the global research agenda of the Swiss National Centre of Competence in Research (NCCR) North–South, as one of this comprehensive research program's 9 Joint Areas of Case Studies (JACS)—namely, the JACS South East Asia.

One of the activity lines of the NCCR North–South in South East Asia is concerned with regional syndrome assessment, a task for which the availability of sound and homogenous regional spatial databases is a crucial prerequisite. In this respect, the Watershed Classification Project (WSCP) carried out by the MRCS between 1989 and 2001 has laid a foundation of utmost importance. The WSCP was funded by the Swiss Agency for Development and Cooperation (SDC) and implemented by the riparian states of Cambodia, Laos, Thailand, and Vietnam, in cooperation with the Centre for Development and Environment of the University of Berne.

A basinwide watershed classification as a spatial reference base

The main objective of the WSCP was to elaborate a basinwide classification indicating the sensitivity of watersheds with regard to resource degradation (mainly by soil erosion), which would serve as a support tool for decision-makers at the national and provincial levels. Based on the topography, various parameters crucial to degradation processes, such as slope, elevation and landform, were linked in an empirical watershed class prediction equation. As a result, the project produced over 20 Gigabytes of geographically referenced vector and raster data taken from 1030 topographic maps at a scale of 1:50,000.

A Digital Terrain Model (DTM) with a resolution of 50 meters was then developed for the entire LMB. From these data, the potential degradation risk was derived for each land unit. Finally, risks were grouped into 5 classes, Watershed Class 1 being the most sensitive and Watershed Class 5 the least sensitive to potential soil erosion. These two Watershed Classes can be considered critical with regard to soil erosion when the land is cleared of natural vegetation; Classes 3 to 5 are regarded as uncritical. Along with the classification, the project produced general recommendations for sustainable land use in each Watershed Class.

  1. Watershed Class 1: Protection Forest Areas with very steep slopes and rugged landforms, commonly uplands and headwater areas. As a rule, these areas should be under permanent forest cover. However, account needs to be taken of traditional rights and land use practices.

  2. Watershed Class 2: Commercial Forest Areas with steep slopes, usually at higher elevations, which are in general less susceptible to degradation than Watershed Class 1. Recommended land uses are forestry (conservation and production forests), agro-forestry, and grazing, if accompanied by strict conservation measures.

  3. Watershed Class 3: Agroforestry Areas with moderate to steep slopes and less erosive land-forms, including uplands and footzones of slopes. May be used for commercial forestry, grazing, and combinations of trees and agricultural crops, if appropriate conservation measures are applied.

  4. Watershed Class 4: Upland Farming Gently sloping lands. Wide range of land uses possible. Moderate need for water and soil conservation depending on local conditions.

  5. Watershed Class 5: Lowland Farming Gently sloping land and flat areas. Suitable, from the point of view of water and soil conservation, for a wide range of land uses such as paddy rice, other agricultural uses, and forestry.

It is crucial to note that in all classes, land uses other than those recommended above are not excluded, provided that adequate care is given to soil conservation. The recommended land use for areas in Class 1, for instance, is forest cover; nevertheless there are many examples clearly proving that forest cover is not the only solution for conserving steep watersheds.

In order to ensure firm integration of techniques and possible interpretations into the respective national institutions of the riparian countries, the WSCP has successfully provided over 40 formal and on-the-job training sessions to the national WSCP teams.

Putting the database to practical use: examples from development, monitoring, and research

With its database, the WSCP has created an enormous potential for further spatial analysis in combination with other datasets (for example satellite imagery), available and ready to be tapped for development planning, implementation, monitoring, as well as training and education purposes (Figure 1). Up to now, it has been combined with various thematical datasets elaborated by the MRCS and other institutions (eg infrastructure, vegetation) and put to use in regional integrated development and monitoring, dam site planning, telecommunication, and many other spheres, by well over 100 national and international institutions, including bilateral development agencies such as GTZ and DANIDA, and multilateral organizations, such as the World Bank and the Asian Development Bank. The WSCP data constitute the best homogenous baseline data available for the Lower Mekong Basin to date.

The WSCP regional database was supplemented by a regional watershed directory presenting key watershed parameters, including slope classes, erosion risk, vegetation cover, population, and infrastructure. This directory, which covers over 100 watersheds in Laos, the Thai part of the Mekong Basin, Cambodia, and Vietnam, has become a major reference base for a number of bilateral development projects.

Finally, the NCCR North–South uses the WSCP regional database for research purposes within two research projects—one dealing with patterns of land cover change in the LMB, and the other with poverty modeling in Vietnam. The valuable baseline data enable these projects to efficiently carry out their research objectives by deriving accessibility and population density models. Along with these mainly research-oriented projects, the NCCR North–South has also elaborated an A3 hardcopy Socioeconomic Atlas of Vietnam (see book review on pp 185–187 of this issue of MRD), a publication intended to further diminish the gap between data, knowledge, information, and informed decision-making, to support mitigation activities in the region.


Typical landscape in a head watershed in northern Laos: 3D view with an aerial photograph taken in 1992, superimposed on Digital Terrain Model. (Figure compiled by Andreas Heinimann)

Andreas Heinimann, Thomas Breu, and Thomas Kohler "Watershed Classification in the Lower Mekong Basin," Mountain Research and Development 25(2), 181-182, (1 May 2005).[0181:WCITLM]2.0.CO;2
Published: 1 May 2005

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