15 - System and component uncertainties in water resources

Summary

ABSTRACT

Management of water resources is inherently subject to uncertainties due to data inadequacy and errors, modeling inaccuracy, randomness of natural phenomena, and operational variability. Uncertainties are associated with each of the contributing factors or components of a water resources system and with the system as a whole. Uncertainty can be measured in terms of the probability density function, confidence interval, or statistical moments such as standard deviation or coefficient of variation. In this chapter, available methods for uncertainty analysis are briefly reviewed.

INTRODUCTION

The planning, design, and operation of water resources systems usually involve many components or contributing factors. Each of the components or factors individually and the system as a whole are always subject to uncertainties. For example, the reliability of flood forecast depends not only on the uncertainty of the prediction model itself but also on the uncertainties on the input data. The design of a storm drain is subject to the uncertainty on the runoff simulation model used, uncertainties on the design storm determination, as well as uncertainties on the materials, construction, and maintenance used. Water supply is always subject to uncertainties on the demand, availability of the sources of water, and the performance of the distribution network. Safety of a dam depends not only on the magnitude of the flood but also on the waves, earthquake, conditions of the foundation, and maintenance and appropriateness of the operational procedure. Numerous other examples can be cited. In short, decisions on water resources are always subject to uncertainties.

Knowledge of uncertainties is useful for rational decision making, for cost-effective design, for safe operation, and for improved public awareness of water resources risks and reliability.