Since 1950, the riparian countries of the Mekong River
have undergone a dynamic change in land-use. Extensive areas of forest
have been logged and cleared for agriculture.
Hamilton (1987) emphasizes the role of scale in measuring
the impacts of land-use practices. They can be classified into three categories
based on the affected area: local level, medium level and macro level.
Impacts occur at the local scale in the area where land-use takes place,
caused e.g. by soil erosion, new fallow zones or areas showing declines
in soil fertility and productivity. Impacts at the medium or macro scale
are e.g. sedimentation and siltation of riverbeds, reservoirs and irrigation
systems, frequency of low flows and floods, deposition of chemical residues
in rivers and lakes. These last-mentioned impacts are more difficult and
complex to manage.
There are only few empirical studies on the relationship between the
removal of forest and land-use changes regarding water yield (low flows,
floods), soil erosion, sedimentation and nutrient load of streams within
the geographical context of the Lower Mekong Basin. Quantitative information
is needed to support decisions in watershed management which includes
management of all natural resources within a watershed for the protection
and production of water resources while maintaining environmental stability.