An assessment of optimal waste load allocation and assimilation characteristics in the Arroyo Colorado River watershed, TX along the US–Mexico border

Effective water quality management requires careful consideration of pollutant fate and transport, proper estimation of non-point source loadings, and maximum allowable allocation of point source discharges. A decision support system (DSS) that addresses all these issues is developed in this study by embedding mass-balance expressions, GIS, and a remote-sensing-based non-point source loading scheme into a hybrid goal-programming approach and is applied to the rapidly growing Arroyo Colorado River watershed along the US–Mexico border. The model components were favorably evaluated against field data and previous studies. The DSS was used to evaluate the carrying capacity of the river, defined based on the water quality standards for biochemical oxygen demand, dissolved oxygen, and minimum in-stream flow requirements. The results indicated that on a macro-scale, the current stresses utilize about 40 % of the maximum carrying capacity. However, the most upstream and downstream sub-watersh