OWRT Project No. A-069-ARIZ / Agreement No. 14-34-0001-6003 / Project dates: July 1975-September 1977 / Acknowledgement: The work upon which this report is based was supported by funds provided by the United States Department of the Interior, Office of Water Research and Technology, as authorized under the Water Resources Research Act of 1978. / A water resources management study for the Sonoita Creek watershed was conducted in order to develop a usable water resources management plan for the area and to resolve possible conflict among the different water demands in the basin. These water demands are classified as municipal and domestic, recreation and agriculture. Six potential water resources management alternatives are developed and compared using the standardized cost -effectiveness methodology. This approach enables thorough and efficient comparison of the alternatives with respect to both quantifiable and unquantifiable criteria. Each alternative considers developing either the ground water or the surface water resources of the watershed. Also, each alternative considers some method of treated sewage effluent disposal. The algorithm ELECTRE I is used to select the most suitable plan for the watershed. This procedure is used because of its simplicity and its proven usefulness in analyzing multiobjective decision problems. With the available information on the ground and surface water resources of the watershed, the choice of alternatives is reduced to one, namely, construction of a small reservoir at Redrock Canyon. Evaporation control measures are needed in order to reduce evaporation losses from the reservoir. The reservoir would serve as a supplemental source of water for the town of Patagonia and for the Sonoita Creek Sanctuary. v