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Section 3: Case studies in land surface evaluation |
Consultant Engineering Geologist, Milford, Guildford, Surrey, UK
Rationale
In remote areas decisions on the need for remedial and maintenance works on linear projects such as roads and canals may involve the evaluation of risk based on the identification and distribution of definable hazards. A terrain model provides the basis for a classification scheme to enable this to be done cost effectively. In addition it facilitates the identification of problem areas that may require more detailed subsequent design investigation. In the absence of more detailed investigation it provides the basis for a conceptual construction approach.
The site
This example relates to hill irrigation schemes in the Himalaya of Nepal and Bhutan and involved the upgrading of existing village canals irrigating between 50 and 200 hectares of agricultural land for rice production. Each canal ran across steep slopes and was experiencing difficulties with slope instability. In the feasibility stage a limited number of projects had to be selected from a large initial listing.
Area model
The Himalaya form part of an active fold mountain belt characterized by moderate to high rates of uplift, regular seismic events and extreme relief. They are also subject to a tropical monsoon climate, at least at lower elevations, which causes significant weathering and erosion.
Mountain-building activity is not uniform but comprises episodes of uplift interposed between quieter periods. In active times rivers rapidly downcut and form steep incised valleys. In quieter periods weathering and slope evolution and more mature rivers result in a less severe landscape. The model in Figure 1 uses this concept to classify the landscape.
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This 250-word extract was created in the absence of an abstract.
