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close this bookThe Himalayan Dilemma: Reconciling Development and Conservation (UNU, 1989, 295 pages)
close this folder6. The Himalayan-lowland interactive system: do land-use changes in the mountains affect the plains?
View the documentIntroduction
View the documentRegional assessment of watershed degradation
View the documentDownstream effects of watershed degradation

Introduction

The previous three chapters have discussed the linkages between those segments of the Theory of Himalayan Environmental Degradation that relate primarily to the physical processes occurring, or that are assumed to be occurring, within the mountains. This chapter focuses on the larger question: assuming that accelerated erosion due to land-use changes is taking place on a vast scale in the mountains, what is the evidence in support of claims for dramatic downstream impacts? We will now attempt to estimate the regional distribution of watershed degradation in the central Himalaya and its hydrological and geomorphic effects downstream.

Much of this chapter depends upon a major data collection and preliminary analysis by Andreas Lautherburg of the University of Berne (Lauterburg and Messerli, 1986, unpublished). During several visits to the region he collected as many data as possible on soil erosion and watershed degradation in Nepal, India, and Pakistan. In addition he collected all available data on stream flow (runoff) and sediment load of the main Himalayan rivers. Much of the critical information was found in publications such as Laban (1978, 1979), Zollinger (1978, 1979), and Carson (1984, 1985), and in the files of four government and international organizations: the Department of Soil Conservation and Watershed Management, HMG, Kathmandu; the Remote Sensing Centre, HMG, Kathmandu; the Central Soil and Water Conservation Research and Training Centre, Dehra Dun, Uttar Pradesh; and the International Centre for Integrated Mountain Development (ICIMOD), Kathmandu.

The data-acquisition phase of the study is by no means complete. This is partly due to time and funding limitations, but also to the fact that many data on hydrology and sediment transfer were not accessible.

The available data can be divided into two groups: direct and indirect. An example of the former is the direct measurement of soil loss from controlled test plots. This kind of information, as indicated in the preceding chapters, is both rare and unreliable (unreliable partly in the sense of lack of representativeness). Nor is it a major contribution for estimating the spatial distribution of degradation on a regional scale. Thus, of more value is the indirect information; examples of this are time series on the suspended sediment load in rivers and the density of landslides per unit area.

Much of Lauterburg's study of erosion records of test plots and small catchments parallels the discussion in Chapter 5. He concludes that, at the local (micro) level, soil erosion is highly influenced by human impact and that corrective measures could reduce this dramatically. We also wish to reemphasize the positive aspects of certain forms of human intervention. Lauterburg also supports our earlier contention that the conversion of mountain lands under natural vegetation to an agricultural landscape does not automatically result in an increase in soil erosion (accelerated erosion) since soil loss is not dependent upon natural versus domesticated soil cover but on a conservation factor; an extreme case, for instance, is the positive influence of carefully tended agricultural terraces. This part of Lauterburg's analysis is taken no further here and we will discuss now the indirect data and its assessment.