Journal of Water Resources Planning and Management

The weighted‐least‐squares method using sensitivity‐analysis technique is proposed for the estimation of parameters in water‐distribution systems. The parameters considered are the Hazen‐Williams coefficients for the pipes. The objective function used is the sum of the weighted squares of the differences between the computed and the observed values of the variables. The weighted‐least‐squares method can elegantly handle multiple loading conditions with mixed types of measurements such as heads and consumptions, different sets and number of measurements for each loading condition, and modifications in the network configuration due to inclusion or exclusion of some pipes affected by valve operations in each loading condition. Uncertainty in parameter estimates can also be obtained. The method is applied for the estimation of parameters in a metropolitan urban water‐distribution system in India.

The genetic algorithm technique is a relatively new optimization technique. In this paper we present a methodology for optimizing pipe networks using genetic algorithms. Unknown decision variables are coded as binary strings. We investigate a three‐operator genetic algorithm comprising reproduction, crossover, and mutation. Results are compared with the techniques of complete enumeration and nonlinear programming. We apply the optimization techniques to a case study pipe network. The genetic algorithm technique finds the global optimum in relatively few evaluations compared to the size of the search space.

A model is developed to estimate the parameters of a lognormal flow‐frequency distribution, and it can include multiple historical or paleoflood periods in which the largest flow within the period is defined and a current gage record. Asymptotic approximations of the variances and covariances of the distribution parameters are presented and used to compute first‐order approximations of the standard deviations of 100‐year and 500‐year floods. The model is applied to gage paleoflood data for Black Bear Creek at Pawnee, Oklahoma. Distribution parameters, their approximate variances and covariance $Q_{100}$ and $Q_{500}$, and their standard deviations were computed. A simulation experiment using 300 samples was performed. The $Q_{100}$ and $Q_{500}$ estimated using the multiple‐period model had lower standard errors than those estimated using either a single‐threshold or gage‐record‐only model. First‐order approximations of the standard deviations of $Q_{100}$ and $Q_{500}$ were compared to the simulation results and the largest error was 13%.

For over two decades, Santa Barbara County, Calif., has been struggling with problems concerning water supply. Within a space of 12 years, there was a major evolution in both expert and lay understanding of local water resources conditions and development alternatives within Santa Barbara County, Calif. As a result of this greater comprehension and easing of certain political pressures, the June 4, 1991, bond elections held throughout various localities on the issue of connecting to California's State Water Project were largely successful, despite the continuing controversial nature of the issue. In contrast, the March 4, 1979, countywide bond election on essentially this same matter (but following a very wet year) had failed miserably according to Lawrance in 1981. This paper summarizes both the inescapable sociopolitical aspects and certain technical aspects of the project alternatives as they evolved over 12 years.

Water law typically evolves through several stages in response to changing demands. Changes are likely to result in reallocation among different interests that compete for water resources. Water law at a given time is not value‐neutral, but favors certain uses over others based on the prevailing values during its formative period. Because of the diffusion of values throughout a water‐allocation system, any change in the system is likely to effect a reallocation of the resource. Significant reallocations have occurred at different times during the history of the eastern states. Most recently, substitution of water‐use permitting programs for common‐law allocation systems has resulted in reallocation from certain types of landowners (such as riparian proprietors) to a broader cross section of society. These changes have strengthened the concept that water is a public resource while eroding the exclusive rights once associated with the ownership of certain property.

A flow‐duration curve (FDC) is simply the complement of the cumulative distribution function of daily, weekly, monthly (or some other time interval of) streamflow. Applications of FDCs include, but are not limited to, hydropower planning, water‐quality management, river and reservoir sedimentation studies, habitat suitability, and low‐flow augmentation. Although FDCs have a long and rich history in the field of hydrology, they are sometimes criticized because, traditionally, their interpretation depends on the particular period of record on which they are based. If one considers $n$ individual FDCs, each corresponding to one of the individual $n$ years of record, then one may treat those $n$ annual FDCs in much the same way one treats a sequence of annual maximum or annual minimum streamflows. This new annual‐based interpretation enables confidence intervals and recurrence intervals to be associated with FDCs in a nonparametric framework.

A multivariate approach for the design of ground‐water monitoring networks is presented. The proposed technique is based on the geostatistical method of cokriging. The network design problem is posed as an optimization model in which the variance of estimation is minimized. The multivariate approach used herein accounts not only for autocorrelations but also for variable cross correlations. By considering a network design in which several variables are jointly monitored, lower monitoring costs are achieved; also, and more importantly, a better estimation of the monitored parameters is yielded given the fact that lower estimation variances are reached. The method used for selecting the optimal monitoring sites is based on a simultaneous search technique using a branch and bound algorithm guaranteeing optimality of the solution. The methodology is applied for the design of a monitoring network to observe aquifer transmissivity (T) and the specific capacity (SC) in the Yolo County Basin, Calif. The results show the superiority of the multivariate geostatistical approach and how it provides a better and more economical network design than the univariate approach.

At culvert entrances and other drainage obstructions the area upstream of the obstruction acts as a reservoir, holding arriving runoff while earlier arriving waters are still passing through. Urban development in a watershed increases storm‐flow volume and peak rate, increasing the potential accumulation of water and hence rising of stage and overflowing. Storm hydrographs with different flow volumes and peak rates were routed through a computer model of a culvert entrance, with the upstream area functioning as a reservoir. Maximum stage rose with increasing flow volume for more than half of the modeled combinations of conditions. Thus in an urbanizing watershed, for a wide range of conditions, the tendency to overflow at an obstruction increases unless volume of flow is suppressed, whether or not peak rate is suppressed by detention. Storm‐water infiltration, which controls both flow volume and peak rate, would be a more complete solution. Storm‐water management policy that is aimed to prevent overflows at drainage obstructions should consider flow volume control in addition to peak rate control.

Drought poses a serious risk to the performance of an integrated municipal water system (MWS), subjecting it to the combined effect of increased demands and decreased supplies. In this study, the performance of an integrated MWS is investigated under two failure scenarios: (1) Available supply less than the required demand; and (2) system capacity less than the demand rate. The reliability bounds approach is used to estimate the overall reliability of integrated MWSs. The use of the reliability bounds to estimate the integrated MWS reliability is a powerful technique for water systems involving multiple failure modes. This analysis provides a set of guidelines for MWS managers to improve system performance. This study finds that pressure requirements of MWSs are frequently the binding constraints on reliability during drought. This conclusion suggests more attention be paid to pressure‐reduction schemes in managing drought impacts.

An application of four multicriterion decision making (MCDM) techniques to a typical ground‐water management problem is presented. Criteria representing pumping yield, total costs, and water‐shortage risk are considered. The management model expressed in such a multicriterion form is based on the finite‐element method and a combined embedding/response matrix method. This model is used to generate a discrete representation of a nondominated solution set. Four MCDM techniques: compromise programming, ELECTRE III, multiattribute utility function, and UTA method representing, respectively, distance‐based, outranking, and utility (multiplicative and additive forms) approaches are examined as potential decision‐aid tools to select the appropriate management scheme. Comparison of the results shows that these quite different MCDM techniques lead to a similar subset of recommended solutions. Adequacy of these techniques for ground‐water management is discussed from the points of view of technique characteristics, decision maker's expectations, analyst's knowledge required, and method output, that is, ranking of alternatives.