Reservoir/River System Reliability Considering Water Rights and Water Quality

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Texas Water Resources Institute

Effective management of the highly variable water resources of a river basin requires an understanding of the amount of suitable quality water that can be provided under various conditions within institutional constraints. Although much research has been reported in the published literature regarding modeling reservoir system operations and evaluating water supply reliabilities, relatively little work has addressed integration of water rights and salinity considerations in comprehensive water availability studies. However, from a practical water management perspective, these are the controlling factors in many river basins in Texas and elsewhere. The study documented by this report provides expanded capabilities for modeling and analysis of reservoir/river system reliability, with a focus on institutional (water rights) and water quality (salinity) considerations.

Population and economic growth combined with depleting ground water reserves are resulting in ever increasing demands on the surface water resources of Texas. Water rights and salinity represent two particularly important considerations in management and utilization of the surface water resources of the state. With the recent implementation of a prior appropriation permit system, water rights have become a key aspect of reservoir/river system management. Natural salt pollution is also a controlling constraint in utilization of the waters of a number of major river basins in Texas and neighboring states.

Surface water law in Texas developed historically over several centuries. Claims have been recognized to water rights granted under Spanish, Mexican, Republic of Texas, and United States, as well as State of Texas, laws. Early water rights were granted based on various versions of the riparian doctrine. A prior appropriation system was later adopted and then modified. An essentially unmanageable system evolved, with various types of water rights existing simultaneously and with many rights being unrecorded. The Water Rights Adjudication Act of 1967 merged the riparian water rights into the prior appropriation system. The allocation of surface water now has been consolidated into a unified permit system. The water rights adjudication process required for transition to the permit system was initiated in 1968 and was completed in the late 1980s. About 7,700 active permits are now in effect for use of the waters of the 15 major river basins and eight coastal basins of the state. Applications for additional new permits or modifications to existing permits can be submitted to the Texas Natural Resource Conservation Commission at any time. Applications are approved only if unappropriated water is available, existing rights are not impaired, a beneficial use is contemplated, water conservation will be practiced, and the water use is not detrimental to the public welfare.

Water quality in several major river basins in the Southwestern United States is seriously degraded by natural salt contamination. The salt, which consists largely of sodium chloride, originates from geologic formations underlying portions of the upper watersheds of the Arkansas, Canadian, Red, Brazos, Colorado, and Pecos Rivers in the states of Kansas, Colorado, Oklahoma, New Mexico, and Texas. Millions of years ago, this region was covered by a shallow inland sea. The salt-bearing geologic formations were formed by salts precipitated from evaporating sea water. Salt springs and seeps and salt flats in the upper portions of the river basins now contribute large salt loads to the rivers. The natural salt pollution significantly impacts water resources development and management.

The Brazos River Basin provides a case study for the research. A water supply reliability study was performed for a system of 12 reservoirs owned and operated by the Brazos River Authority and U.S. Army Corps of Engineers. The evaluation of the water supply capabilities of the 12-reservoir system reflects the facts that: (1) over a thousand entities, owning about six hundred reservoirs, hold permits to use the waters of the Brazos River and its tributaries and (2) much of the streamflow is unsuitable for most beneficial uses much of the time due to excessively high salt concentrations.

The Brazos River Basin illustrates a general situation which is characteristic of other major river basins as well. A significant need exists for improving modeling and analysis capabilities for performing comprehensive water availability studies. Reservoir/river system reliability analyses support planning studies and management decisions regarding (1) improvements in reservoir system operating policies, water rights allocations, and water supply contracts, (2) facility expansions and construction of new water supply projects, and (3) projects and strategies for dealing with salinity. Formulation and implementation of innovative management strategies for operating reservoir systems, allocating water between multiple uses and users, and minimizing the adverse impacts of natural salt pollution require that a river basin be treated as an integrated system.