The report presents the status of risk based hydrologic designs that have been reported in literature and based on these, identifies a computational procedure for developing hydrologic design bases for dams and spillways. Some illustrative examples are presented in order to demonstrate the impact of risk based analysis on current design practices.
Decision making in water resources is most often a deterministic selection of dimensions, which divide the probability distribution of the controlling variable into two regions: performing well and failing to perform. Interpretation of nature is deterministic, stochastic or mixed. Various deterministic hydrologic concepts have been used particularly for design of major hydraulic structures. The need exists for bridging the deterministic and stochastic approaches to solving various water complexities, explain why they have not yet been fully introduced into the practice of decision making.
A brief overview of the hydrologic design criteria adopted by some of the government agencies in India and abroad for safety evaluation of dams is presented. It is shown that the hydrologic design basis resulting from a risk based analysis may not always be in conformity with applicable hydrologic design criteria. In addition to that, some of the limitations of the performance of an accurate risk-based analysis are presented.
The decision-making process, which is based on four attributes: benefit, cost, selected technology, and risk and uncertainty is expected to play a significant role in the future development of water resources. Risk analysis is an analytical process, which complements and aids planning evaluation and design as well as regulatory cost effectiveness analysis. It is not being paid attention to in most hydrological designs risk analysis.
Considering the enormous cost of construction of hydraulic structures, and other social, legal, environmental and engineering considerations, as well as safety aspects, there is an urgent need for adoption of risk based hydrologic design procedures. Risk analysis must fit within a broader evaluation framework, whether it is benefit-cost analysis, multi-objective analysis or standard based cost effectiveness analysis. Therefore, risk analysis should be embedded in formal approaches which deal with risk cost trade-offs.
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