Uncertainty of hydraulic parameters

Reliability analysis and other probabilistic techniques are becoming increasingly important tools in hydraulic modeling and decision making. Probabilistic and reliability analyses are based on knowledge of the underlying parameter uncertainties. Hydraulic variables, such as roughness coefficient, channel slope, and critical shear stress, common to many hydraulic-engineering problems, are known to contain considerable uncertainty. However, careful evaluation of the levels of uncertainty has not been conducted for many of these and other variables. Therefore, the underlying assumptions of uncertainty for a reliability-based design may be in error, causing significant error in the computed reliability or probability of failure. The main objective of the present study is to quantify various hydraulic parameter uncertainties in terms of the coefficients of variation and associated distributions. Significant advances are being made in reliability and probabilistic methods and their use in hydraulic and hydrologic engineering is rapidly increasing. If the uncertainties that underlie any of these methods cannot be properly defined, the results of the reliability analysis are inaccurate.