Journal of Water Resources Planning and Management

Existing rational metrics of performance used to identify optimal reservoir management policies are examined to determine if they adequately measure the desirability of a water release strategy. It is shown that such performance metrics, while regarded as providing a rational framework for decision making, may in fact only be nominally rational and in fact at odds with the true attitudes and perceptions of the decision makers and users affected by the water releases. This situation is particularly relevant for reservoirs designed and operated to supply water to irrigation projects. A means for a more complete representation and evaluation of the possible consequences associated with a release decision is therefore necessary. A model capable of replicating the manner in which risks associated with release decisions are perceived, interpreted, and compared by a decision maker is proposed. The model is based upon neural network theory and enables the more complete representation of the risk of a particular decision to be considered in making decisions on reservoir releases.

Knowledge of anticipated demands for water is a crucial element in water planning. The logical sequence in water resources planning is to examine the present demands of water for all purposes, to determine how the demand in various sectors will be affected by growth, and then to project what the water demands will be in the short- and long-term future. The first part of this paper deals with Egypt's water demands, with each aspect being calculated for the present and future. In the second part, an effort is made to quantify the water from each possible source to estimate the potential for future water supply. Balances are then examined with possible combinations of policies and scenarios leading to numerous planning alternatives. The conclusion is that Egypt is water secure until 2000, remedial measures will extend this until 2020, and beyond that additional surface supply is essential. Finally, the water shortages or excesses are quantified and recommendations are made based on the most probable future directions.

This paper summarizes the methods and results of economic analyses performed for the agency responsible for water supply development and operation in Libya in support of decisions regarding further investments in water supply systems in their country. This study identified least-cost combinations of investments in Libya's Great Man-made River Project (GMRP) together with desalination that would meet specified water demand targets at various demand sites in the country. The GMRP is one of the largest civil works projects in the world, involving the pumping of ancient ground water from the Sahara Desert and transporting it hundreds of kilometers to the coast of Libya where demands for water exist. The paper outlines the optimization models used in these analyses and presents some interesting outcomes that warrant additional studies focusing on capacity expansion over time. Given the investments already made in the GMRP, only under most optimistic cost scenarios does desalination appear to be an economically efficient expansion alternative and then only for a limited range of water demands.

An interim drainage structure provides short service during the construction months of the permanent drainage structure. This study presents a risk-cost approach by which the design flood for an interim drainage structure can be derived from the capacity of the permanent structure, cost-capacity ratio, cost-damage ratio, and construction months during a year. To accommodate various construction periods in a year, the design capacity for such a temporary drainage structure can be adjusted to the monthly rainfall or runoff distribution at the project site. Design charts were produced for the break-even economic condition using the Gumbel distribution for annual maximum analysis. Similar solutions were also achieved using the Exponential distribution for annual exceedance analysis. Design methodology presented in this paper provides an objective basis for selecting construction months and sizing the interim drainage structures.

Field sampling is sometimes performed to support modeling activities—specifically, to estimate the parameters of a mathematical model or, more accurately, to calibrate the model. In this case, a relevant question for field samplings design is “how to maximize the confidence in estimated parameter values, given a level of sampling effort?” We approach this question using established ideas in parameter estimation and sampling design theory and propose general sensitivity-based methods to rank the locations and types of measurements for estimating the parameters of a water distribution network model. The proposed methods are suboptimal, yet practical, and are applied to select good tracer and pressure measurement locations for estimating pipe roughness coefficients. These particular results suggest that, when compared to pressure measurements, tracer measurements can be informative for calibrating network hydraulic parameters but one must take more care in selecting their location. Using the proposed methods, a selection of both tracer and pressure measurements improves estimation confidence by a factor of 2, over that obtained using tracer or pressure measurements alone.

Conventional landfill design attempts to control the downward seepage of leachate by using low permeability liners. The rate of leachate seepage into the underlying ground-water system can be controlled by decreasing the permeability of soil liners and/or by using synthetic membranes to form an additional barrier to leachate migration. However, loss of leachate from conventional landfills is likely to occur due to the inherent limitations of natural materials and the inevitable imperfections of installing synthetic liners. The artesian landfill liner system eliminates the downward seepage by reversing the direction of the hydraulic gradient so that seepage occurs into, and not out of, the landfill. A conceptual cost model incorporates the trade-offs between the capital cost of constructing robust liners and the operational costs of supplying recharge water and treating additional leachate produced by the artesian hydraulics. In addition, a two-dimensional, transient finite-element flow model demonstrates that the reverse hydraulic gradient limits the loss of leachate even if the integrity of the landfill liner is imperfect or deteriorates over time.

An increasing number of states use permit programs to coordinate and to control water resource allocations. A general approach is suggested for allocating and permitting water withdrawals in a river basin. A mathematical programming methodology facilitates optimal streamflow allocation while maintaining desired levels of instream flow. The approach uses a graphical tool, the flow duration curve, to illustrate the quantity and frequency of joint streamflow withdrawals in a river basin. The methodology is unique because while it uses mathematical programming methods, it is implemented using a spreadsheet optimization tool, Microsoft Excel Solver, and the solution is illustrated in a graphical form so that nontechnical individuals can easily understand the methodology results. The ability to apply the methodology and clearly explain the results is extremely important since many nontechnical individuals are involved as policymakers in water allocation decisions.