Browsing by Author "Carriere, Patrick E."
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Item Evaluation of Storage Reallocation and Related Strategies for Optimizing Reservoir System Operations(Texas Water Resources Institute, 1988-08) Carriere, Patrick E.; Wurbs, Ralph A.Statement of the Problem Rapid population and economic growth combined with depleting groundwater reserves are resulting in ever increasing demands on surface water resources in Texas, as well as elsewhere. The climate of the state is characterized by extremes of floods and droughts. Reservoirs are necessary to control and utilize the highly variable streamflow. Due to a number of economic, environmental, institutional, and political considerations, construction of new reservoir projects is much more difficult now than in the past. Consequently, optimizing the beneficial use of existing reservoirs is becoming increasingly more important. Reservoir operation is based on the conflicting objectives of maximizing the amount of water available for conservation purposes and maximizing the amount of empty space available for storing future flood waters to reduce downstream damages. Common practice is to operate a reservoir for either flood control only, conservation only, or a combination of flood control and conservation with separate pools designated for each. The conservation and flood control pools, or vertical zones, in a multipurpose project are fixed by a designated top of conservation (bottom of flood control) pool elevation. Conservation pools may be shared by various purposes, such as water supply, hydroelectric power, and recreation, which involve both complementary and conflicting interactions. Public needs and objectives and numerous factors affecting reservoir operation change over time. An increasing necessity to use limited storage capacity as effectively as possible warrants periodic re-evaluations of operating policies. Reallocation of storage capacity between purposes represents a general strategy for optimizing the beneficial use of limited storage capacity in response to changing needs and conditions. A storage reallocation between flood control and conservation purposes typically involves a permanent or seasonal change in the designated top of conservation pool elevation. Reallocations between conservation purposes can be achieved by various modifications of operating policies. Although given relatively little consideration in the past, storage reallocations will likely be proposed more frequently as demands on limited resources increase. Scope of Study This report documents an investigation of: (1) the potential of storage capacity reallocation and other related modifications in operating policies as management strategies for optimizing the beneficial use of existing reservoirs in Texas and (2) modeling capabilities for formulating and evaluating such changes to operating policies. In general, storage reallocations can involve a variety of types of reservoir use. The present study focused primarily on flood control and water supply. Multiple purpose reservoir operations involving hydroelectric power were also investigated. Both permanent conversion of storage capacity between purposes and seasonal rule curve operations were addressed. Buffer pool operations were also considered. Multiple reservoir system operation was a major emphasis of the study. The literature was reviewed and several reservoir management agencies contacted to (1) identify experiences in studying and/or implementing storage reallocations and (2) evaluate the state-of-the-art of associated modeling and analysis capabilities. The feasibility of seasonal rule curve operation depends upon the seasonal characteristics of the various factors affecting reservoir operation. Precipitation, streamflow, reservoir evaporation, water demands, and reservoir storage content data for Texas were analyzed to identify seasonal characteristics. A 12-reservoir system operated by the U.S. Army Corps of Engineers and Brazos River Authority provided a case study for evaluating the potential for storage reallocations and related operating strategies. This system, located in the Brazos River Basin, is considered representative of major reservoirs in Texas. The existing operating policies and possible modifications were investigated. The case study includes (1) flood control storage frequency and conservation drawdown frequency analyses based on the results of monthly hydrologic period-of-record simulations of reservoir system operations and (2) firm yield and reliability analyses. The generalized computer programs HEC-3, HEC-5, STATS, and MOSS-IV, and several utility software packages were used in the modeling study. Simulation of reservoir system operations was based on an 85-year sequence of monthly hydrologic data. The case study provides a preliminary assessment of the viability of permanent storage conversions and/or adoption of seasonal rule curve operations as potential reservoir management strategies. The objective is to evaluate storage reallocation potentialities in general, not develop detailed reallocation plans. The case study is basically a reconnaissance-level hydrologic analysis of reservoir operations. The monthly period-of-record simulations provide a reasonably precise analysis of water supply considerations. However, the daily hydrologic data required for detailed analysis of flood control operations were not included in the study. Reallocation of reservoir storage capacity involves complex institutional, financial, economic, legal, political, and technical considerations not addressed in the case study. However, the hydrologic analyses provide a good starting point for determining what types of reallocation strategies and modeling approaches might be potentially effective and whether more detailed studies are worthwhile. Organization of the Report Chapter 2 is a general discussion of reservoir operation and institutional and technical aspects of storage reallocation and a review of reallocations which have been implemented or proposed throughout the nation. Chapter 3 addresses the seasonality of the hydrologic factors pertinent to seasonal rule curve operation in Texas. Chapter 4 reviews state-of-the-art modeling capabilities and describes the computer models adopted for use in the case study. The Brazos River Basin case study is presented in chapters 5 through 8. Study results are summarized, and conclusions are presented in chapter 9.Item Hydrologic and Institutional Water Availability in the Brazos River Basin(Texas Water Resources Institute, 1988-08) Walls, W. Brian; Carriere, Patrick E.; Bergman, Carla E.; Wurbs, Ralph A.Statement of the Problem Effective management of its surface water resources is essential to the continued growth and prosperity of the state of Texas. Rapid population and economic growth combined with depleting ground water reserves are resulting in ever-increasing demands being placed upon the surface water resources. The climate of the state is characterized by extremes of floods and droughts. Reservoirs are necessary to control and utilize the highly variable streamflow. Numerous reservoirs have been constructed to facilitate management of the water resources of the various river basins of the state. Effective control and utilization of the water resource supplied by a stream/reservoir system requires an understanding of the amount of water which can be provided under various conditions. Estimates of reservoir yield are a key element in practically all studies and decisions involving development and management of surface water supplies. Yield is defined as the amount of water which can be supplied by an unregulated stream, reservoir, or multiple reservoir system during a specified period of time. The stochastic nature of streamflow must be reflected in methods for quantifying yield. The approaches for expressing yield which traditionally have been used in water supply planning and management are firm yield and, to a lesser extent, reliability. Firm yield is the estimated maximum release or withdrawal rate which can be maintained continuously during a repetition of the hydrologic period-of-record. A number of definitions of reliability are cited in the technical literature. A common definition is that reliability is the percentage of time that a stream/reservoir system is able to meet a specified demand. Precise textbook definitions of firm yield and reliability can be formulated for a simple river basin with one reservoir and one water user. However, in actual practice, for a complex multiple reservoir, multiple user system, firm yield and reliability must be defined in terms of the basic assumptions and approaches used in handling various complicating factors. Water supply planning and management involves complex institutional, environmental, hydrologic, and physical systems. Streamflow, reservoir sedimentation, evaporation, water demands, and other variables pertinent to yield determinations are highly stochastic. Measured historical data is limited in extent and accuracy. The future is always uncertain. Mathematical models only approximate the complexities of reality. Consequently, reservoir yield studies necessarily involve uncertainties and approximations. The availability of water to particular users depends upon legal rights and contractual commitments as well as physical facilities and hydrologic conditions. Reservoir yield is subject to institutional as well as hydrologic constraints. Evaluation of the relationships between water rights and reservoir yield is particularly important at this time in Texas with the recent completion of the water rights adjudication process. Scope of the Study The objective of the study documented by this report was to evaluate and improve state-of-the-art capabilities for estimating reservoir yield. Institutional as well as hydrologic aspects of water availability were investigated. Evaluation of increases in yield achieved by multiple reservoir system operation, rather than separate operation of individual reservoirs, was a major emphasis of the study. The river basin was viewed as an integrated system. The hydrologic and institutional availability of water was investigated for a case study reservoir system. However, the study approach and computer programs used are generally applicable to any reservoir system. Study findings have pertinent implications for water resources management throughout Texas and elsewhere as well as for the specific river basin studied. Water availability is dependent upon institutional constraints and capabilities. The study included a review of water law and other institutional aspects of surface water management in Texas. A literature review was made assessing modeling capabilities for estimating reservoir yield. The reservoir system simulation models HEC-3 and HEC-5 were adopted for use in the case study. These generalized computer programs provide comprehensive capabilities for analyzing the hydrologic aspects of reservoir system operations, but lack the capability to simulate water rights priorities. Consequently, a generalized water rights simulation computer program was developed in conjunction with the study. Other computer programs were used for developing input data and analyzing output from the HEC3, HEC-5, and water rights models. A system of twelve reservoirs in the Brazos River Basin provided a case study. Nine multiple purpose flood control and conservation reservoirs are owned and operated by the Fort Worth District (FWD) of the U.S. Army Corps of Engineers (USACE). The Brazos River Authority (BRA) has contracted for most of the water supply storage capacity of the nine federal projects. The BRA owns and operates three other conservation reservoirs. In addition to the 12-reservoir USACE/BRA system, Hubbard Creek Reservoir, owned by the West Central Texas Municipal Water District, was modeled in detail because of its relatively large storage capacity. The numerous other smaller reservoirs in the basin were considered primarily from the perspective of approximating their impacts on the 12 USACE/BRA reservoirs. Individual reservoir and system firm yields were computed based on alternative conditions of reservoir sedimentation and alternative assumptions regarding multiple reservoir and multiple user interactions. The sensitivity of firm yield estimates to these and other factors was evaluated. A series of yield analyses were made from a strictly hydrologic perspective, without consideration of water rights. Yield analyses were then repeated incorporating water rights constraints. In addition to the firm yield simulations, a basinwide water rights analysis simulation study was performed. The simulations were based on monthly historical period-of-record hydrologic data. The modeling studies provided a basis for evaluating the hydrologic and institutional availability of water in the Brazos River Basin. Organization of the Report An overview of water law and institutions in Texas, from the perspective of surface water Management, is presented in Chapter 2. Surface water Management in the Brazos River Basin is described in Chapter 3. Chapter 4 is 8 discussion of reservoir system yield analysis models in general and the models used in the present study in particular. The Brazos River Basin simulation studies are documented by Chapters 5 through 9. Chapter 5 describes the compilation of basic data used in the study. A detailed hydrologic yield study is documented by Chapter 6. The analyses outlined in Chapter 6 were performed with HEC-3 and HEC-5 and are from a strictly hydrologic perspective, without consideration of water rights. The water rights analyses, utilizing the TAMU Water Rights Analysis Progra , are presented in Chapters 7 and 8. Chapter 7 discusses the results of a simulation of hydrologic and water rights aspects of surface water management in the basin. Firm yields constrained by senior water rights are documented in Chapter 8. Chapter 9 provides a critical evaluation, including sensitivity analyses, of the key factors affecting firm yield estimates. The study summary and conclusions are presented as Chapter 10.