Natural Salt Pollution and Water Supply Reliability in the Brazos River Basin

The Brazos River Basin is representative of several major river basins in the Southwestern United States in regard to natural salt pollution. Geologic formations underlying portions of the upper watersheds of the Brazos, Colorado, Pecos, Canadian, Red, and Arkansas Rivers, in the states of Texas, Oklahoma, New Mexico, Kansas, and Colorado, are sources of salt emissions to the rivers. 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 upstream areas of the basins now contribute large salt loads to the rivers. The natural salt contamination significantly impacts water resources development and management.

Water quality in the Brazos River is seriously degraded by natural contamination by salts consisting largely of sodium chloride with moderate amounts of calcium sulfate and other dissolved solids. The primary source of the salinity is groundwater emissions in an area of the upper basin consisting of the Salt Fork Brazos River watershed and portions of the adjacent Double Mountain Fork Brazos River and North Croton Creek watersheds. High salt concentrations significantly affect water management and utilization. Water in the three main stream reservoirs is unsuitable for municipal use without costly desalinization processes. The quality of the river improves significantly in the lower basin with dilution from good quality tributaries.

Population and economic growth combined with depleting groundwater reserves are resulting in ever-increasing demands on the surface water resources of Texas and the Brazos River Basin. Effective management of the highly stochastic water resources of a river basin requires an understanding of the amount of suitable quality water which can be provided under various conditions. Reservoir 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 salt pollution. Consideration of water quality as well as quantity is important in evaluating reservoir system reliability in the Brazos River Basin.