Multi-objective risk assessment of freshwater inflow on ecosystem sustainability in San Antonio Bay, Texas



N. B. Chang; G. Parvathinathan;B. Dyson


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Abbreviated Journal Title

Water Int.


environmental flow; ecological systems; systems analysis; multi-objective programming; risk assessment; water resources management; ESTUARIES; OPTIMIZATION; NEEDS; Engineering, Civil; Water Resources


San Antonio Bay is located on the coast of Texas between Galveston Bay and Corpus Christi Bay and is the primary bay in the Guadalupe Estuary. Three rivers feed San Antonio Bay from two river basins, including the Blanco and Guadalupe Rivers in the Guadalupe River Basin and the San Antonio River in the San Antonio River Basin. The Canyon Reservoir regulates the flow of fresh water in the middle and lower reaches of the Guadalupe River These inflows are a primary regulator of salinity and, thus,,the productivity of commercially important estuarine species. Increasing demand for water has prompted plans for an increased diversion of 49.3 million m(3) (40, 000 acre-feet) from the reservoir An additional amount of 61.6 million m(3) (50,000 acre-feet) from the mouth of the river is to be pumped back to, San Antonio to relieve over-pumping of the Edwards Aquifer. Because the Guadalupe River Basin contributes 58.1 percent of the freshwater inflow to the estuary, it is not known what the impact of these actions will have on the ecological integrity of the San Antonio Bay. Water resource management in the San Antonio Basin consists of decision making under risk and uncertainty related to randomness in the critical parameters such as the salinity in the bay, biological productivity, and total flow into the bay. The aim of this study is to investigate the trade-offs between the competing objectives of maximizing biological,productivity in the bay and minimizing flow using Stochastic Compromise Programming (SCP). The SCP model solves a multi-objective function subject to constraints that must be maintained at three different Prescribed levels of probability providing a global set of solutions for the water resource management problem under input uncertainty. The SCP model provides information on the trade-offs among the objective function value, tolerance values of the constraint at the prescribed levels of probability, which could be valuable to policy makers in risk assessment. Solutions were found using three distance functions. Model outputs may suggest the minimum amount of freshwater needed to maximize biological productivity of the bay at specified risk level for assessing the impact of upcoming diversion program. Results indicate that current flows in the Guadalupe River are of sufficient volume to satisfy harvest requirements.

Journal Title

Water International





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