Water Resources System Performance Research Articles

The influence of climate variations on an irrigation water resources system performance strategy

The influence of climate change on the performance strategy of an irrigation water resources system (WRS) containing a reservoir cascade is discussed as a decision-making problem under uncertainty. There are: (1) a set of climate change scenarios and (2) a set of river runoff sequences and a set of irrigation demand sequences with various statistical characteristics (sets (2) correspond to every scenario (1)). The function of transfer from the scenarios to the sequences is defined as certain subjective probabilities. The probabilities reflect the degree of the expert confidence in the plausibility of hydrology and moistening hypothesis. There is an index showing the degree of departure of WRS performance from the normal and from the worst values. The proposed technique allows us to (a) generate hydrology and water demand scenarios; (b) calculate the subjective probabilities; (c) compute the irrigation rates as a function of precipitation, radiation balance, etc., and then to compute of irrigation demand schedules; (d) to simulate the WRS. The algorithms of water resources distribution between the users and of WRS operation with stochastic water demands were implemented in a simulation model. The Terek river basin (North Caucasus, Russia) was taken for sample computations.

Reliability, resiliency, and vulnerability criteria for water resource system performance evaluation

Three criteria for evaluating the possible performance of water resource systems are discussed. These measures describe how likely a system is to fail (reliability), how quickly it recovers from failure (resiliency), and how severe the consequences of failure may be (vulnerability). These criteria can be used to assist in the evaluation and selection of alternative design and operating policies for a wide variety of water resource projects. The performance of a water supply reservoir with a variety of operating policies illustrates their use.

Estimating resilience by canonical analysis

Canonical correlation analysis is used to formulate linear estimates of independent or orthogonal (incremental) information on the performance of water resource systems. Simple economic and resilience indicators are compared, and for the particular configurations chosen in this paper the replicated and independent information sets are explained in terms of the connectivity of the various reservoirs. The canonical correlations are relatively high, indicating that there is significant replication of information; a taxonomy is developed which suggests those basin and structural characteristics which would indicate less replication and consequently improved description of system performance. The procedure is based on simulation studies reported in an earlier paper in this series.

Some properties of variance reduction techniques where hydrological extremes are estimated by Monte Carlo Simulation

An estimate of a water resource system's performance, when it is derived by simulation using synthetic streamflow sequences, is subject to at least three errors: first, model errors, arising from the approximation to the ‘true’ streamflow mechanism which the model represents; second, sampling errors in the model parameters θ when they are calculated from the historic records; and third, errors introduced by the Monte Carlo calculation from which is derived. This paper presents some observations on the effects of the first two types of error on the estimate but concentrates on the application of variance reduction techniques to the derivation of Monte Carlo estimates for given θ. These techniques are, first, the use of control variates and, second, the use of antithetic variates, and their application is illustrated by using some hypothetical examples of the calculation of probabilities of extreme hydrological events and of the calculation of reliability measures for a much oversimplified storage system. Considerable reduction in the variance of resulted from the application of the control variate method; the reduction in Var resulting from the use of antithetic variates was much less but still probably worth the small additional programing effort required. It is concluded that the promise of the control variate method suggests that it should be applied to assist in the efficient simulation of more realistic water resource systems than the trivial ones considered in this paper.

Relative Importance of Variables in Water Resources Planning

Four variables involved in the water resources planning decision characterized by hydrology, modeling of dissolved oxygen behavior in an estuary, projection of economic development, and water quality objective, were tested for sensitivity in the evaluation of a water resources system's performance. The results were obtained assuming a 25% range in economic projection, 1 mg/1 range in the dissolved oxygen objective, two separately developed models of estuarial dissolved oxygen behavior, and 50‐ and 10‐year sequences of hydrologic data. The results of simulations of system operation with the different values of the planning variables were subjected to a four‐way analysis of variance to partition the variance attributable to each planning variable. For the system under consideration, the relative importance of the variables in descending order is: (1) economic development projection, (2) water quality objective, (3) dissolved oxygen modeling, and (4) hydrology.