This paper investigates the effects of uncertainty in the design of hydraulic structures in an open-channel system for irrigation water delivery. Uncertainty due to ambiguity in the values of physical parameters and due to vagueness in the specification of system performance objectives (adequacy, efficiency, dependability and equity) is modeled. Two design objectives, maximum performance and minimum cost, are considered in a simple illustrative example. Implications for design and analysis of large-scale delivery networks in an uncertain environment are discussed.