Journal of Water Resources Planning and Management

A conjunctive‐use model is developed to maximize water user's return under limited and dynamic water supply for long‐term conditions. Salt distribution in the crop root zone is modeled and its effect on crop yield is also taken into account in the model. The main objective of this conjunctive‐use study is to find the optimal ground‐water extraction for stabilizing the water table at specific depths below land surface, while at the same time supplementing the surface irrigation supply. Concepts of limited and stressed irrigation are used to maximize net return. A daily crop water stress index is used to quantify crop yield reduction due to water stress over the growing season of a crop. Yield reduction due to salinity is calculated from the weighted average salinities (electrical conductivity) of applied waters. Salt distribution and transport in crop root zone are modeled using the physical soil properties and mass balance.

In this paper, we outline the framework of a decision support system (DSS) for water‐system designers dealing with water‐quality and water‐supply decisions. These decisions include the efficient acquisition, distribution, treatment, and reuse of water resources as well as the disposal of effluent. Normally, the use of computer models requires each modeler to decide on a specific compromise between solvability and adequate representation of the problem. The designer must then implement that compromise with the computer. The DSS concept presented here offers the designer the option to explore the trade‐offs between these two choices. As a result, the designer's background and knowledge become an integral part of the solution process. The paper includes a description of the steps required to use the DSS. In addition, the paper provides a discussion of the necessary and important role of the system designer.

The drought management plan (DMP) for the lower Colorado River of Texas is described. The plan identifies how the Lower Colorado River Authority (LCRA) will allocate stored water in the Highland Lakes of central Texas to meet projected water demands for year 2000 for rice irrigation, municipal, and other uses during a repetition of the most severe drought ever recorded. The irrigation planning model (IPM) is formulated to determine the optimal areas to cultivate, to maximize the net income of the rice producers when water supplies are limited. The IPM is solved, using mixed‐integer linear programming, for a range of values for water availability to create planting decision tables. These tables are incorporated into the daily stream and reservoir hydrologic simulation model RESPONSE, to evaluate the hydrologic impacts of alternative reservoir operating rules for allocating irrigation (interruptible) stored water supplies from the Highland Lakes. Through repeated simulations, a DMP reservoir operating rule is developed, which maximizes available interruptible water during the critical drought and meets all municipal and other higher‐priority water demands.

A three‐step modeling approach is presented for comprehensive analysis of the planning problem involving integrated use of surface and ground water in irrigation. Applicability of the approach is illustrated by a case study of the Bagmati River Basin in Nepal. In the first step, a stochastic dynamic programming model, which considers most of the interacting processes of the conjunctive‐use system, is used to derive the long‐term operation policy guidelines for alternative plans. Then, a lumped simulation model is used to evaluate the alternative plans and policies, considering a number of mutually related synthetic sequences of streamflow and rainfall. Various economic (cost and benefit) as well as risk‐related (reliability, vulnerability, and resiliency) performance measures and their tradeoffs are evaluated. Finally, a multiple‐criteria decision‐making method (compromise programming) is used to select the most satisfactory alternative plan for indicating the system design (pumping and diversion canal) capacities and water allocation policies, Important policy and management implications are drawn from sensitivity analyses with respect to unit pumping cost, irrigation system efficiency, and recharge coefficient.

Water‐quality policy in the United States includes the concept of a mixing zone, a limited area or volume of water where initial dilution of an aqueous pollutant discharge occurs. Given a myriad of possible discharge configurations, ambient environments, and mixing‐zone definitions, the analyst needs considerable training and expertise to conduct accurate and reliable mixing‐zone analysis. The Cornell Mixing Zone Expert System is a series of programs developed to predict the dilution and trajectory of submerged single‐port (CORMIX1), multiport diffusers (CORMIX2), and surface (CORMIX3) discharges of arbitrary‐density (positive, neutral, or negative) into a stratified or uniform‐density ambient environment with or without crossflow. CORMIX gathers the necessary data, checks for data consistency, assembles and executes the appropriate hydrodynamic simulation models, interprets the results of the simulation in terms of the legal requirements including toxic discharge criteria, and suggests design alternatives to improve dilution characteristics. In particular, CORMIX correctly predicts highly complex discharge situations involving boundary interactions, dynamic bottom attachments, internal layer formation, and buoyant intrusions, all features that are beyond the predictive capabilities of other currently available initial mixing models.

This paper examines the role of the Lesotho Water Resources Act of 1978 in national development. The paper concludes that the act could be very effective in promoting equitable and efficient use of water resources in the country if it is properly implemented. However, effective implementation of the act is hampered by the lack of fiscal resources, especially those involving personnel, transportation, and hardware for the Office of Water Rights. Some of the strategies to increase the effectiveness of the act include strengthening the enforcement capability of the Office of Water Affairs and educating the population about the implications of the act. Also, the act must be integrated into an overall rural development strategy to be effective.