**6.3 Modeling environment and interface features**

A model for a particular reservoir/river system consists of a generalized modeling system and an input dataset describing the reservoir/river system. The generalized modeling system provides an environment or framework for assembling input data, executing the simulation computations, and organizing, analyzing, and displaying results.

Each of the four modeling systems has its own unique framework within which the user constructs and implements a model for a particular reservoir/river system. With ResSim, various elements provided by watershed setup, reservoir network, and simulation modules are used to construct and execute a model. MODSIM is based on network flow programming with a reservoir/river system represented by a network of nodes and links with information compiled through an object-oriented interface. WRAP is about managing programs, files, input records, and results tables, with water management and use practices being described in the terminology of water rights. RiverWare has an object/slot-based environment for building models within the context of object oriented programming and provides three optional solution options.

The user interfaces of the models reflect both similarities and significant differences. ResSim, RiverWare, and MODSIM provide sophisticated graphical user interfaces with menu-driven editors for entering and revising input data and displaying simulation results in tables and graphs and features allowing a river/reservoir system schematic to be created by selecting and connecting icons. WRAP has a simple user interface for managing programs and files, which relies upon standard Microsoft Office programs for entering, editing, and displaying data. WRAP as well as ResSim connect with and rely upon graphics capabilities of the Hydrologic Engineering Center (HEC) Data Storage System (DSS). Geographic information system (GIS) tools are included in all four of the modeling systems.

The compiled executable software products were developed in the programming languages shown in Table 2. ResSim, MODSIM, and RiverWare also have their own simulation rule language to allow users to express reservoir/river system operating requirements as a series of statements with if-then-else and similar constructs.

Data management efficiency, effective communication of results, documentation, and easeof-use are important factors in applying a modeling system. Documentation includes both instructions for using the software and detailed technical documentation for understanding modeling methods. The software should be as near error-free as possible assuming absolutely error-free software may be an idealistic goal yet to be achieved. Dealing with errors introduced by users in model input data is important. The modeling systems contain various mechanisms for detecting and correcting blunders and inconsistencies in input data.

The organizations and individuals that originally developed the four modeling systems continue to improve the models and support their application. ResSim, MODSIM, and WRAP software and manuals are available free-of-charge at the websites listed in Table 1. Licensing fees and training required to implement RiverWare are described at its website. The HEC periodically provides training courses in the application of HEC-ResSim. The TWRI periodically provides training courses in the application of WRAP.

RiverWare is designed for Unix workstations but is also used on personal computers with Microsoft Windows. The other three modeling systems are usually executed on personal computers with Microsoft Windows but can also be applied with other computer systems.
