Journal of Water Resources Planning and Management

Hydrologic, hydraulic, and economic uncertainties impact the economic attractiveness of flood-risk management projects. In particular, uncertainty in the calculation of expected annual damages introduces uncertainty into economic evaluations. This study develops a hypothetical basin to explore the performance of designs identified by different economic-risk decision models. A new decision model includes an explicit quantification of uncertainty in the marginal net benefits and hence in the reliability of net benefits generated by the last increment of a project. Monte Carlo analyses show that the uncertainty in total project benefits may not reveal large uncertainties associated with the last increments of a project. In terms of economic performance of the different descriptions of hydrologic risk, expected probability and traditional maximum likelihood flood-risk estimators are roughly equivalent. The new decision model identified less costly projects that achieved nearly the same average net benefits and had a greater probability of recovering the last dollar spent.

A screening model for selecting and sizing potential reservoirs and hydroplants on a river basin is presented. The system is designed to meet annual irrigation and hydropower demands at prescribed levels of reliability. The model is developed with a focus on considerations that are important to the Indian decision makers. A linked simulation-optimization framework is used for formulation. Sizing of reservoirs and hydroplants, and evaluation of objective function and constraints and their derivatives are done as part of simulation. For sizing reservoirs, a new sequent trough algorithm is used that considers evaporation losses automatically. Generator capacities are determined by maximizing the local net revenues produced from hydropower generation. Derivatives are evaluated using automatic differentiation that produces exact derivatives with minimal human effort. The resulting formulation is applied to Par, Auranga, Ambica, and Purna river basins located in India. Comparison of model solutions with those of the state agency shows that the present formulation leads to a reduction in the system storage and cost of its development.

A simple method has been devised to incorporate the El $\mathrm{Ni}ño$ Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) climate signals into the well-known extended streamflow prediction forecasting approach. Forecasts of ENSO are currently available up to a year or more in advance, which facilitates forecasting of the streamflow response to this climate signal at interannual forecast lead times. The biomodal phase of the PDO can be identified in real time using a combination of assumed persistence of the existing phase and the tracking of extreme events to identify transitions. The technique makes use of a gridded meteorological data set to drive a macroscale hydrology model at 1° spatial resolution over the Columbia River Basin above The Dalles. A streamflow forecast ensemble is created by resampling from the historical meteorological data according to six predefined PDO/ENSO categories. Given a forecast of the ENSO climate signal for the coming water year and the existing phase of the PDO, these meteorological ensembles are then used to drive the hydrology model based on the initial soil and snow conditions as of the forecast date. To evaluate the technique, a retrospective forecast of the historic record was prepared (1989–1998), using October–September as the forecast period, as well as an ensemble forecast for water years 1999 and 2000 that were prepared on June 1, 1998 and May 10, 1999, respectively. The results demonstrate the increase in lead time and forecast specificity over climatology that can be achieved by using PDO and ENSO climate information to condition the forecast ensembles.

Disposal of contaminated dredged material may pose risks to ecological and human populations. These risks are highly uncertain. Measures to confine the dredged material and reduce these risks are likely to increase disposal costs. Risk and cost assessments for dredged material management alternatives often are associated with very large uncertainties. These uncertainties must be explicitly incorporated into risk-cost analysis to ensure that appropriate management alternatives are selected. However, considering these uncertainties may cause difficulties in decision making by making management alternatives effectively indistinguishable. A risk-cost analysis methodology that evaluates uncertainty directly in the decision framework is developed. A multicriteria decision-making method that incorporates uncertainties using fuzzy set theory, is proposed to trade-off risks and costs (including uncertainties) so that disposal alternatives can be compared and selected.

A new approach for reliability-based optimization of water distribution networks is presented. The approach is capable of recognizing the uncertainty in nodal demands and pipe capacity as well as the effects of mechanical failure of system components. A probabilistic hydraulic model is used in the model to account for uncertainty in nodal demands and pipe capacity. The primary innovation of the model is the use of a first-order reliability-method-based algorithm to compute approximate values of the capacity reliability of water distribution networks. Capacity reliability is defined as the probability that the nodal demand is met at or over the prescribed minimum pressure for a fixed network configuration under random nodal demands and random pipe roughnesses. The model also incorporates a strategy for identifying the critical nodes on which the reliability constraints are imposed in the cost minimizing step. The computational efficiency of the optimization is shown to be enhanced by deriving the first-order derivatives analytically using a sensitivity-analysis-based technique. The efficiency and capacity of the proposed algorithm are illustrated by application to two sample networks.

The Aral Basin environmental crisis in Central Asia has been described as the world's largest man-made disaster. This paper examines the causes of the Aral Sea crisis and examines some of the major nontechnical and planning issues that need to be overcome if the crisis is to be effectively managed. It argues that present plans are inadequate for the complexity and size of the task and highlights the need for an effective integrated river basin plan based on a sound planning process. It also draws attention to a significant number of nontechnical issues that will need to be addressed before any plan can become effective.

The Saint-Venant equations of open-channel flow were linearized using the Taylor series and a finite-difference approximation of the original nonlinear, partial differential equations. Using the linear optimal control theory, a proportional-plus-integral (PI) controller was developed for an irrigation canal with five pools. Since the order of the controller gain matrix was large, the Kalman filter was designed to estimate values for the state variables that were not measured. For this problem, there were a total of 45 state and five control variables. With two flow depth measurements per pool, values for the remaining 35 state variables were estimated using the Kalman filter. The simulated canal dynamics with the regional PI controllers along with the local Kalman filter were compared with the performance of the global control algorithms for achieving a constant-volume control and a constant-level control of an example irrigation canal. The performance of the regional constant-volume control algorithms was found to be as good as the performance of the global control algorithm, whereas the performance of the regional constant-level control algorithm was marginally acceptable.

To size storm-water detention basins, a volume-based method such as that of the Federal Aviation Administration is applicable to small urban catchments. However, the reliability of such a method depends on estimation of the average outflow. In this study, the average outflow from a detention basin is found to be related to the time of concentration of the catchment and the duration of the design storm. This modification eliminates judgment calls and warrants a consistency in volumes and flow rates between the design rainfall hyeotograph and the inflow and outflow hydrographs.