**1. Introduction**

This comparative review of capabilities for computer simulation of the control, allocation, and management of the water resources of river basins focuses on user-oriented generalized modeling systems developed in the United States that are applicable anywhere in the world. The objectives of this chapter are to assist practitioners in selecting and applying models in various types of river/reservoir system management situations and to support research in continuing to improve and expand modeling capabilities. The chapter begins with a broad general review of the massive literature and then focuses on comparing several generalized modeling systems that have been extensively applied by water management agencies in a broad spectrum of decision-support situations. Modeling capabilities are explored from the perspectives of computational methods, model development environments, applications, auxiliary analyses, and institutional support. The chapter highlights advances in modeling complex issues in managing rivers and reservoirs that are significantly contributing to actual practical improvements in water management.

Reservoir/river system modeling encompasses various hydrologic, physical infrastructure, environmental, and institutional aspects of river basin management. Dams and appurtenant structures are required to control highly fluctuating river flows to reduce flooding and develop reliable water supplies. Institutional mechanisms for allocating and managing water resources are integrally connected to constructed facilities. Management of the water and related land and environmental resources of a river basin integrates natural and manmade systems.

This review of computer modeling of river system development and management focuses on user-oriented generalized modeling systems developed in the United States. *Generalized* means that a model is designed for application to a range of concerns dealing with river systems of various configurations and locations, rather than being site-specific customized to a particular system. Model-users develop input datasets for the particular river basin of interest. *User-oriented* implies that a model is designed for use by professional practitioners other than the model developers and is thoroughly tested and well documented. Useroriented generalized modeling systems should be convenient to obtain, understand, and use and should work correctly, completely, and efficiently.

Generalized Models of River System Development and Management 5

which is most often historical hydrology representing natural unregulated conditions. River basin hydrology is represented by stream flow inflows and net reservoir surface

evaporation-precipitation rates for each time step of a hydrologic period-of-analysis.

Fig. 1. Illustrative schematic of a river system as viewed from a modeling perspective

multiple-year drought.

management strategies and practices.

The hydrologic simulation period and computational time step and may vary greatly depending on the application. Storage and flow hydrograph ordinates for a flood event occurring over a few days may be determined at intervals of an hour or less. Water supply capabilities may be modeled with a monthly time step and many-year hydrologic period-ofanalysis reflecting a full range of fluctuating wet and dry periods including extended

A river/reservoir system model simulates a physical and institutional water management system with specified conditions of water demand for each sequential time step of a hydrologic period-of-analysis. Post-simulation stream flow and reservoir storage frequency analysis and supply reliability analysis capabilities are typically included in the modeling systems addressed by this chapter. Reservoir storage and stream flow frequency statistics and water supply reliability metrics are developed for alternative river/reservoir system

Other auxiliary modeling features are also, in some cases, incorporated in the river/ reservoir management models. Some models include features for economic evaluation of system performance based on cost and benefit functions expressed as a function of flow and storage. Stream inflows are usually generated outside of the reservoir/river system management model and provided as input to the model. However, reservoir/river system models may also include capabilities for simulating precipitation-runoff processes to generate inflows. Though hydraulics issues may be pertinent to reservoir operations, separate models of river hydraulics are applied to determine flow depths and velocities.

This state-of-the-art assessment begins with a brief overview of the extensive literature and then focuses on the four modeling systems listed in Table 1. ResSim, MODSIM, WRAP, and RiverWare were developed and are extensively applied in the United States, are also applied in other countries, provide a broad range of analysis capabilities, and are representative of the state-of-the-art from the perspective of practical applications dealing with complex river systems. The four alternative modeling systems reflect a broad spectrum of computational methods, modeling environments, and analysis capabilities.


Table 1. Selected representative generalized modeling systems
