Planning for Dams

Careful planning throughout the siting, design, and construction of dams is necessary for optimal utilization of rivers and for preventing catastrophic dam failure . These planning phases require input from engineers, geologists, hydrologists, ecologists, financiers, and a number of other professionals.
Designers must first evaluate alternative solutions and designs for meeting the same desired objective, whether the goal is to allocate water supply, improve flood control, or generate electricity. Each alternative requires a comprehensive cost-benefit analysis and feasibility study for evaluating its physical, economic, ecological, and social impact.
Once an alternative has been selected, a number of important considerations enter into the design and construction of the dam. These include:

• Hydrological evaluation of climate and streamflows;
• Geologic investigation for the foundation design;
• Assessment of the area to be inundated by the upstream lake (also called a reservoir) and its associated environmental and ecological impacts;
• Selection of materials and construction techniques;
• Designation of methods for diverting stream flow during construction of the dam;
• Evaluation of the potential for sediments to accumulate on the reservoir bottom and subsequently reduce storage capacity; and
• Analysis of dam safety and failure concerns.

When a dam is put into operation, or commissioned, water is released from the upstream reservoir over a spillway or through gates in a manner to satisfy intended objectives. Operating rules for maximizing power generation, for example, include maintaining hydraulic head. In contrast, water levels in flood control reservoirs must be periodically reduced to allow for new storage during anticipated periods of flood hazard. Operating issues, however, can easily become complex and highly politicized and may be difficult to resolve. This is particularly true for river systems containing several reservoirs, for dams serving multiple purposes, and in cases where adverse social, ecological, and environmental impacts are significant.


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