7.1.1 Uncertainties in Hydraulic Engineering Design

In designing hydraulic engineering systems, uncertainties arise in various aspects including, but not limited to, hydraulic, hydrologic, structural, environmental, and socioeconomical aspects. Uncertainty is attributed to the lack of perfect knowledge concerning the phenomena and processes involved in problem definition and resolution. In general, uncertainty arising because of the inherent randomness of physical processes cannot be eliminated and one has to live with it. On the other hand, uncertainties, such as those associated with the lack of complete knowledge about processes, models, parameters, data, and so on, can be reduced through research, data collection, and careful manufacturing.

Uncertainties in hydraulic engineering system design can be divided into four basic categories: hydrologic, hydraulic, structural, and economic (Mays and Tung, 1992). Hydrologic uncertainty for any hydraulic engineering problem can further be classified into inherent, parameter, or model uncertainties. Hydraulic uncertainty refers to the uncertainty in the design of hydraulic structures and in the analysis of the performance of hydraulic structures. Structural uncertainty refers to failure from structural weaknesses. Economic uncertainty can arise from uncertainties in various cost items, inflation, project life, and other intangible factors. More specifically, uncertainties in hydraulic design could arise from various sources (Yen et al., 1986) including natural uncertainties, model uncertainties, parameter uncertainties, data uncertainties, and operational uncertainties.

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