Environmental Engineering Reference
In-Depth Information
The consequences of landsliding on the outer parts of the storage rim may include:
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Constraints on operation of the storage;
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Damage to existing property or infrastructure;
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Damage to a saddle dam or its foundations (Cabrera, 1992), or
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In an extreme case, breaching of the rim, causing loss of storage and flooding of land.
It is clear that the possibility of landsliding is an important feasibility issue for storage proj-
ects. However, from examination of 145 reservoir landslides case histories, ICOLD(2002)
has reported that:
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Only about 36% of the known reservoir landslides were recognised during the plan-
ning stage investigations;
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At least 75% of the known reservoir landslides were pre-existing dormant or occa-
sionally active or active features, and
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Such pre-existing slides cause the most problems for reservoir owners.
These figures indicate that the planning stage studies for some reservoir projects have
been seriously ineffective. Recognising this, ICOLD (2002) has compiled guidelines on the
identification and treatment of reservoir landslides, and management of the risks they creat.
The guidelines are aimed at both owners of existing projects, and planners of future projects.
They include 89 pages of text, figures and tables, 9 pages of references and 4 appendices. They
cover all of the relevant issues, as follow:
1. International experience - case histories in Appendix A;
2. Management;
3. Geological and geotechnical investigations;
4. Slope assessment and analysis;
5. Impulse waves and valley blockage;
6. Risk management and risk mitigation;
7. Monitoring;
8. Operational requirements.
The authors commend the guidelines to readers. Assuming their availability and use by
those involved with storage projects, the following text is limited to views on the timing
of storage area stability studies, and some strategies for managing instability issues should
they become evident.
2.11.1
Vital slope stability questions for the Feasibility and Site Selection Stages
The authors consider it vital that the following questions be answered with confidence, by
the end of Stage 2, Feasibility and Site Selection (see Chapter 4).
1. Which features (existing or proposed) and/or parts of the storage would be most vul-
nerable to landsliding, should this occur when the storage is filled or operated?
2. Which, if any, parts of the storage area rim show evidence of a) currently active lands-
liding, or b) old, dormant landslides which may become reactivated?
3. Which parts of the storage area rim may be susceptible to first time landsliding?
4. For each feature or area defined by the answers to 1 to 3 above, what is the assessed
probability of landsliding, when the storage is filled and operated?
5. For each potential landslide, what is the likely volume, velocity and travel distance?
6. For each such feature or area, what are the assessed consequences of landsliding, under
those conditions?
