**5.4 RiverWare reservoir and river operation modeling system**

The U.S. Bureau of Reclamation (USBR) and Tennessee Valley Authority (TVA) jointly sponsored development of RiverWare at the Center for Advanced Decision Support for Water and Environmental Systems (CADSWES) of the University of Colorado (Zagona et al., 2001; Zagona et al., 2006). RiverWare development efforts date back to the mid-1990's, building on earlier software developed at CADSWES that extends back to the mid-1980's.

RiverWare provides the model-user with a software tools for constructing a model for a particular river/reservoir system and then running the model that include a library of modeling algorithms, solvers, and a language for coding operating policies. The tools are applied within a point-and-click graphical user interface. RiverWare routs inflows, provided as input, through a system of reservoirs and river reaches. The primary processes modeled are volume balances at reservoirs, hydrologic routing in river reaches, evaporation and other losses, diversions, and return flows. Optional features are also provided for modeling groundwater interactions, water quality, and electric power economics.

Computational algorithms for modeling reservoir/river system operations are based on three alternative approaches: (1) pure simulation, (2) rule-based simulation, and (3) optimization combining linear programming with preemptive goal programming. Pure simulation solves a uniquely and completely specified problem. In rule-based simulation, certain information is generated by prioritized policy rules specified by the model-user. Preemptive goal programming considers multiple prioritized objectives based on multiple LP solutions (Eschenbach et al., 2001). As additional goals are considered, the optimal solution of a higher priority goal is not sacrificed in order to optimize a lower priority goal.

Generalized Models of River System Development and Management 17

function coefficients in MODSIM and the RiverWare LP option may optionally be economic costs or benefits. MODSIM and WRAP simulate salinity. RiverWare options include various water quality constituents. Groundwater sources and channel losses are included in the models. Surface/ground water interactions have been approximated in various ways. MODSIM has a groundwater routine, and has been linked with the U.S. Geological Survey

System analysis models are often categorized as being prescriptive or descriptive. With the exception of the optimization option in RiverWare, the four models are essentially descriptive simulation models that demonstrate what will happen if a specified plan is adopted. Prescriptive optimization models automatically determine the plan that will best satisfy the decision criteria. Although it may be desirable for models to be as prescriptive as possible, real-world complexities of reservoir system operations typically necessitate model orientation toward the more descriptive end of the descriptive/prescriptive spectrum.

The term *ad hoc* in Table 2 refers to computational strategies developed specifically for a particular model, as contrasted with linear programming (LP) which is a generic algorithm incorporated in numerous models. ResSim and WRAP are organized based upon ad hoc model-specific computational frameworks. MODSIM is based on network flow LP. RiverWare has two alternative solution options based on ad hoc algorithms and a third option that uses LP. The LP-based models have additional ad hoc algorithms used along with their LP solver, but the LP solver accounts for a major portion of the computations.

Repetitive loops and iterative solution procedures are incorporated in all of the models. Iterative algorithms are required for evaporation and hydropower computations. Evaporation depends upon end-of-period storage, but end-of-period storage depends upon evaporation. Reservoir storage volume versus surface area and elevation relationships are nonlinear. In the LP models, the entire LP solution of the whole system is repeated iteratively. With the ad hoc simulation procedures, the computations for an individual

Modeling Programming Computational Computational System Language Approach Time Step

ResSim Java ad hoc 15 minutes to day MODSIM C++.NET, Basic.NET network LP month, week, day WRAP Fortran ad hoc month, day, other RiverWare C++ ad hoc and LP hour to year

ResSim and RiverWare generally follow an upstream-to-downstream progression in considering requirements for reservoir storage and releases, diversions, and hydropower generation. WRAP and MODSIM simulation computations are governed by user-specified priorities in considering water management requirements. The WRAP and MODSIM priority-based frameworks are beneficial in modeling complex water allocation systems.

MODFLOW groundwater model.

**6.2 Computational structure** 

reservoir are repeated iteratively.

Table 2. Alternative development frameworks

The TVA applies RiverWare in optimizing the daily and hourly operation of the TVA system of multiple-purpose reservoirs and hydroelectric power plants. The USBR has used RiverWare as a long-term planning model and mid-term operations model of the Colorado River as well as a daily operations model for both the Upper and Lower Colorado Regions. The USBR has also applied the model in the Rio Grande, Yakima, and Truckee River Basins. The USACE has recently sponsored addition of features to RiverWare for simulating flood control reservoir operations. Other entities have also applied the model in various river basins for various purposes.
