EL ROL DEL CANTANTE SOLISTA

Review of Reservoir/River System Models

The federal water agencies, state and regional water agencies, private firms, research institutes, and universities have developed numerous reservoir/river system analysis models. Development and application of modeling systems are often partnership efforts involving multiple organizations. Models evolve over time with improved and expanded versions. Chapter 6 provides a broad overview addressing both past and current models representative of the evolving state-of- the-art over the past several decades. Although several site-specific models are cited, the emphasis is on generalized models. Although the research literature is also reviewed, the primary focus of the chapter is to inventory available generalized reservoir/river system models that are being applied in actual practice.

Literature of Reservoir/River System Modeling

Pioneering efforts in computer simulation of reservoir/river systems in the United States include a Corps of Engineers study of the operation of the six main-stem reservoirs on the Missouri River initiated in 1953 (Manzer and Barnett 1966). The objective was to maximize hydroelectric power generation subject to constraints imposed by specified requirements for navigation, flood control, and irrigation. Shortly thereafter, both the Corps of Engineers and Bonneville Power Administration conducted simulation studies of hydropower operations on the Columbia River. The International Boundary and Water Commission simulated a multiple-purpose two-reservoir system on the Rio Grande in 1954. A simulation study for the Nile River Basin in Egypt in 1955 considered alternative plans with as many as 17 reservoirs or hydropower sites. The objective was to determine the particular combination of reservoirs and operating procedures that would maximize the volume of useful irrigation water (Manzer and Barnett 1966). Maass et al. (1966), Hufschmidt and Fiering (1966), and Reuss (2003) discuss the pioneering simulation modeling work of the Harvard University Water Program. Numerous other computer models of river/reservoir system operations have been developed since these early endeavors.

A tremendous amount of work on developing and applying reservoir/river system models has been documented in the published literature during the past 50 years. Much additional work has been accomplished without being reported in the published literature. Several general references that provide a broad state-of-the art review of reservoir/river system modeling capabilities are noted in this section. Other references dealing with specific models are cited later in the chapter.

The several books on modeling and analysis of reservoir operations include those by McMahon and Mein (1986), Votruba and Broza (1989), Wurbs (1996), ReVelle (1999), and Nagy et al. (2002). The author of this report has also prepared previous state-of-the-art reviews of reservoir system analysis methods (Wurbs et al. 1985; Wurbs 1990, 1993, 1994, 1996). The Texas Natural Resource Conservation Commission (TNRCC), its partner agencies, and a team of consultants performed a comparative evaluation of available models in the process of adopting a generalized model for the Texas Water Availability Modeling System (TNRCC 1998). The U.S. Bureau of Reclamation (USBR) maintains a Hydrologic Modeling Inventory (HMI) that provides descriptions of reservoir and river system operations models along with other categories of models. The original USBR HMI was distributed as a printed report (1991). The periodically updated inventory is maintained at the following web site: http://www.usbr.gov/pmts/rivers/hmi/

The published research literature on modeling reservoir system operations is dominated by applications of optimization techniques. The Allies organized interdisciplinary teams during World War II to solve complex scheduling and allocation problems involved in military operations. Mathematical optimization models were found to be very useful in this work. After the war, the evolving discipline of operations research continued to rely heavily upon optimization models for solving a broad range of problems in private industry. The same mathematical programming techniques also became important tools in the various management science and systems engineering disciplines, including water resources systems analysis. Mathematical programming is covered by numerous operations research and mathematics books as well as civil engineering systems books (ReVelle and McGarity 1997; Revelle et al. 2004) and water resources systems books (Loucks et al. 1981; Mays and Tung 1992; Karamouz et al. 2003; Jain and Singh 2003).

Reservoir system operations have been viewed by researchers as having high potential for beneficial application of an array of mathematical optimization techniques. Many hundreds of journal and conference papers have been published since the 1960's on applying variations of linear programming, dynamic programming, gradient search algorithms, heuristic programming models such as genetic algorithms, and other nonlinear optimization techniques to reservoir system analysis problems. Various probabilistic methods for incorporating the stochastic nature of streamflows and other variables in the optimization models have been proposed. Yeh (1985) and Labadie (1997 and 2004) provide concise summary reviews of this extensive and complex research literature.

Inventory of Generalized River/Reservoir System Models

The following review focuses on generalized models that have been applied by water management agencies to support actual planning and/or operations decisions. Several models representative of current state-of-the-art modeling capabilities are listed in Tables 6.1 and 6.2. These models have been extensively applied by water management agencies and their consultants to major reservoir systems over many years to support complex decision processes. The ten models listed in Table 6.1 along with a number of other models are briefly discussed in Chapter 6. The five models listed in Table 6.2 are described in greater detail in Chapter 7.

A number of other models not listed in Tables 6.1 and 6.2 are cited in the remainder of this chapter. Many hundreds of other models reported in the literature are not cited at all in this report. The models listed in Tables 6.1 and 6.2 are representative of current modeling capabilities and have a record of successful application by water management agencies in support of actual decision making. In comparing the models listed in the tables to the many others discussed in this chapter or reported in the literature, the other models may fall within one of the following categories.

1. Other models may provide similar capabilities as the models listed. The models listed in Tables 6.1 and 6.2 are representative of capabilities reflected in various other models as well. 2. Other models may provide additional capabilities not provided by those listed. In some cases,

the additional capabilities have been adopted in practice. However, most of the many hundreds of models that fall in this category are based on mathematical programming and stochastic modeling techniques that have been explored extensively by university researchers but adopted relatively little by the water management agencies.

Table 6.1 Generalized Reservoir/River System Models Discussed in Chapter 6 Short Name Descriptive Name Model Development Organization

Models Developed by the Corps of Engineers

HEC-5 Simulation of Flood Control and Conservation Systems

USACE Hydrologic Engineering Center http://www.hec.usace.army.mil/

HEC-PRM Prescriptive Reservoir Model USACE Hydrologic Engineering Center http://www.hec.usace.army.mil/

SSARR Streamflow Synthesis and Reservoir Regulation

USACE North Pacific Division

http://www.nwd-wc.usace.army.mil/report/ssarr.htm

Models Developed by State Agencies

WRIMS (CALSIM)

Water Resources Integrated Modeling System

California Department of Water Resources

http://modeling.water.ca.gov/hydro/model/description.html StateMOD State of Colorado Stream

Simulation Model

Colorado Water Conservation Board and Colorado Division of Water Resources, http://cdss.state.co.us/

Models Developed by International Consulting Firms and Research Institutes

OASIS Operational Analysis and Simulation of Integrated Systems

HydroLogics, Inc.

http://www.hydrologics.net/ ARSP Acres Reservoir Simulation

Program

Acres International, BOSS International

http://civilcentral.com/html/arsp_tech_info.html MIKE BASIN GIS-Based Decision Support for

Water Planning & Management

Danish Hydraulic Institute

http://www.dhisoftware.com/mikebasin/ RIBASIM River Basin Simulation Delft Hydraulics, http://www.wldelft.nl

WEAP Water Evaluation and Planning Stockholm Environment Institute, http://weap21.org

Table 6.2 Generalized Reservoir/River System Models Discussed in Chapter 7 Short Name Descriptive Name Model Development Organization

SUPER SWD Reservoir System Model USACE Southwestern Division http://www.swd.usace.army.mil/ HEC-ResSim Reservoir System Simulation USACE Hydrologic Engineering Center

http://www.hec.usace.army.mil/

RiverWare River and Reservoir Operations Bureau of Reclamation, TVA, CADSWES http://animas.colorado.edu/riverware/ MODSIM Generalized River Basin

Network Flow Model

Colorado State University

http://modsim.engr.colostate.edu/modsim.html

WRAP Water Rights Analysis Package Texas Commission on Environmental Quality, USACE, TWRI, http://ceprofs.tamu.edu/rwurbs/wrap.htm

Several of the models cited in the remainder of this chapter are predecessors of those listed in Table 6.2. The models have long histories of improvements in response to expanding applications and advances in computer technology. In the process of continual evolution, several of the models listed in Table 6.2 are gradually replacing other legacy software cited in this chapter.

Models Developed by the U.S. Army Corps of Engineers

The Hydrologic Engineering Center (HEC), Waterways Experiment Station (WES), and the division and district offices of the U.S. Army Corps of Engineers (USACE) have extensive experience in modeling reservoir/river system operations. HEC-ResSim and SUPER are described in Chapter 7. Several other USACE models are cited in the following discussion.

USACE Hydrologic Engineering Center Models

HEC-ResSim, the newest HEC generalized reservoir/river system simulation model, is covered in Chapter 7. HEC-3 and HEC-5 discussed below are HEC-ResSim predecessors. HEC- PRM, also included in the following discussion, represents a significantly different modeling approach and has not been as widely applied as HEC-3/HEC-5/HEC-ResSim. The HEC models are used in combination with the HEC-DSS Data Storage System described in Chapter 5, which provides input data preparation and output analysis capabilities (Hydrologic Engineering Center 1995, 2003). ResSim may be applied either separately or in combination with other HEC models either as an integral component of the Corps Water Management System (CWMS) or independently thereof.

Corps Water Management System (CWMS)

The Corps Water Management System (CWMS) is a modernized version of the HEC water control management software system (Fritz et al. 2002). Development of the CWMS was initiated in FY 1997, and the initial version was completed in 2001. CWMS is a comprehensive system incorporating the acquisition, transformation, verification, storage, display, analysis, and dissemination of information to support real-time operations of Corps of Engineers flood control and multiple-purpose reservoir systems. Components of the CWMS include:

• real-time and static data acquisition systems

• data storage in a database managed with the ORACLE software system

• data visualization tools for creating tables, plots, charts, and maps

• dissemination of information using web sites and other mechanisms

• simulation models

Several simulation models from the HEC family of generalized models are incorporated in the CWMS. This integrated suite of models include:

∗ HEC-HMS (Hydrologic Modeling System) simulates watershed hydrology using observed and predicted precipitation to generate streamflow hydrographs at pertinent locations.

∗ HEC-ResSim (Reservoir System Simulation) models reservoir operations for inflows developed with HEC-HMS.

∗ HEC-RAS (River Analysis System) computes river stages at pertinent locations based on the flows from HEC-HMS and HEC-ResSim.

∗ HEC-FIA (Flood Impact Analysis) uses the results from HEC-RAS along with economic data to assess the impacts of flooding for various ResSim operating scenarios.

The CWMS is being implemented in the 43 USACE district and division offices (Davis 2003). The Lower Colorado River Authority (LCRA) of Texas is the first non-USACE agency to adopt the CWMS (Ickert and Luna 2004). LCRA and HEC have entered into an agreement for HEC to support LCRA in implementing of the modeling system for the six LCRA operated reservoirs on the Colorado River upstream of the City of Austin. LCRA's initial use of the CWMS was for flood control planning studies. The LCRA CWMS-based modeling system is being expanded to include real-time reservoir operations for flood control.

HEC-3 and HEC-5

The HEC-3 Reservoir System Analysis for Conservation program simulates operation of reservoir systems for conservation purposes such as water supply, low-flow augmentation, and hydroelectric power. The initial version of HEC-3 was developed in 1965-1966. The Hydrologic Engineering Center has not distributed HEC-3 in recent years because essentially all of its capabilities have been duplicated in HEC-5. HEC-3 and HEC-5 have similar capabilities for simulating conservation operations, but HEC-3 does not have the comprehensive flood control capabilities of HEC-5. HEC-3 is documented by a users manual (Hydrologic Engineering Center 1981) and other HEC publications.

The HEC-5 Simulation of Flood Control and Conservation Systems program has been used in many Corps and non-Corps studies, including investigations of storage reallocations and other operational modifications at existing reservoirs as well as feasibility studies for proposed new projects. The program is also used to support real-time operations. An initial version released in 1973 has subsequently been greatly expanded. The Fortran programs have been run on various computer systems over the years. The HEC-5 package includes several utility programs to aid in developing input data files and analyzing output. Alternative versions of the model exclude and include water quality analysis capabilities. The HEC-5 users manual (Hydrologic Engineering Center 1998) provides instructions for its use. Various HEC publications regarding the use of HEC- 5 include training documents covering various features of the model and reports and papers documenting specific applications of the model in actual reservoir system analysis studies.

HEC-5 simulates the sequential period-by-period operation of a multiple-purpose reservoir system for inputted sequences of unregulated streamflows and reservoir evaporation rates. Multiple reservoirs can be located in essentially any stream tributary configuration. The program uses a variable time interval. For example, monthly or weekly data might be used during periods of normal or low flows in combination with daily or hourly data during flood events. The user specifies the operating rules in HEC-5 by inputting reservoir storage zones, diversion and minimum instream flow targets, and allowable flood flows. The model makes release decisions to empty flood control pools and to meet user-specified diversion and instream flow targets based on computed reservoir storage levels and streamflows at downstream locations. Seasonal rule curves and buffer zones can be included in the operating rules. Multiple-reservoir release decisions are

based on balancing the percent storage depletion in specified zones. Hydrologic flood routing options include modified Puls, Muskingum, working R&D, and average lag. HEC-5 has various optional analysis capabilities including computation of expected annual flood damages and single- reservoir firm yields for water supply and hydroelectric power.

HEC-PRM Prescriptive Reservoir Model

The HEC Prescriptive Reservoir Model (HEC-PRM) is a network flow programming model designed for prescriptively oriented applications. Improved network flow computational algorithms have been developed in conjunction with the model. The optimization model minimizes a cost based objective function. Reservoir release decisions are made based on minimizing costs associated with convex piecewise linear penalty functions (dollars versus storage or flow) associated with various purposes including hydroelectric power, recreation, water supply, navigation, and flood control. Schemes have also been devised to also include non-economic components in the basically economic HEC-PRM objective function. User-specified lower and upper bounds on flows and storages are reflected in the constraint equations. HEC-PRM is generalized for application to any reservoir system (Hydrologic Engineering Center 1994).

HEC-PRM applications to date have used a monthly time interval with historic period-of- record streamflows. Unlike most of the other simulation models discussed in this report, HEC- PRM performs the computations simultaneously for all the time intervals. Thus, model results show a set of reservoir storages and releases which would minimize cost (as defined by the user-inputted penalty functions) for the given inflow sequences assuming all future flows are known as release decisions are made during each period. Since in the real-world, future streamflows are not actually known when a release decision is made, the model provides an upper limit or best possible scenario on what can be achieved. Although the model provides only one set of decision variable values, combinations of a range of values for each variable may result in the same value of the objective function. Various strategies are adopted for using HEC-PRM results to develop alternative reservoir system operating plans and then to evaluate the plans in more detail using a descriptive simulation model (Hydrologic Engineering Center 1994 and 1995; Lund and Ferreira 1996).

HEC-PRM was developed in conjunction with USACE studies of major reservoir systems in the Missouri and Columbia River Basins (Hydrologic Engineering Center 1992 and 1993). Recent applications include a study of the Panama Canal (Hydrologic Engineering Center 1999), the USACE Central and South Florida Project Comprehensive Review Study (Watkins et al. 2004), and non-USACE studies in California (Draper et al. 2003; Jenkins et al. 2004).

Both the Missouri and Columbia River studies involved evaluations of the operations of existing reservoir systems motivated by water shortages during droughts that exacerbated the competition among water users. Application of the HEC-PRM to the system of six mainstem Missouri River reservoirs addressed competing interests that included lake recreation, hydroelectric power generation, flood control, water supply, and downstream navigation and environmental concerns (Hydrologic Engineering Center 1992; Lund and Ferreira 1996). The major environmental concern is maintenance of steady flows for sand bar nesting birds.

HEC-PRM was applied in conjunction with the Columbia River System Operation Review, involving 14 reservoirs, that was conducted by the Corps of Engineers, Bureau of Reclamation, and Bonneville Power Administration (Hydrologic Engineering Center 1993; Hayes et al. 1993). For the Columbia River Basin study, the HEC-PRM objective function reflects cost-based piece-wise linear convex penalty functions representing hydropower, flood control, navigation, anadromous fish, water supply, and recreation. The primary environmental concern is maintenance of seasonal flows to aid in the migration of salmon and steelhead. The hydroelectric power penalty function is expressed in terms of dollars versus both flow and storage. The penalty functions for each of the other uses are expressed in terms of dollars per unit of monthly flows. The penalty functions vary monthly to reflect seasonal characteristics. The objective is to minimize total system costs. Basin hydrology is represented by gaged monthly streamflows for the period of 1928 to 1978, adjusted to represent 1980 conditions of basin development. Various alternative system operation scenarios were evaluated.

The HEC applied the HEC-PRM at the request of the USACE Jacksonville District and South Florida Water Management District to the Central and Southern Florida Project (Watkins et al. 2004). This system completed in the mid-1969's includes about 1,000 miles of levees, 150 water control structures, and 16 major pump stations. The project provides flood control, water supply for agricultural and urban uses, prevention of salt water intrusion, water supply for Everglades National Park, and protection of other fish and wildlife resources. The objective of the restudy supported by HEC-PRM was to develop a plan for improving environmental quality and urban and agricultural water supply reliability. The generalized network flow model was used to evaluate several proposed storage and conveyance plans.

Draper et al. (2003) and Jenkins et al. (2004) describe an optimization model of California's major water systems that was performed at the University of California at Davis under the sponsorship of several agencies. The model called CALVIN consists of HEC-PRM, datasets for California, and supporting utility programs. The model covers water use by 92% of California's