Document Type


Publication Date

January 1975


The Colorado River Bain contains the most diverse environment setting of any American river. High mountainous elevations (>14,000 feet) are ultimately succeeded by sea level plains and low valleys. Geological structures and formations include deep, intricately carved river canyons, high mountain slopes, large saline shale structures, and long verdant irrigated river valleys. Fir forests are succeeded by arid rangelands. The river produces the lowest outflow per unit area (60 acre feet per square mile) of any river basin in the United States. It contains the largest number of unique and endangered species in the United States. Finally, it is the most utilized, most managed, and probably most politicized river in the United States. These characteristics all provide severe constraints on water quality in the river, water uses by society, availability of water and in the possible benefits and other impacts of the Federal Water Pollution Control Act Amendments of 1972 (PL 92-500) on the Colorado River Basin ecosystem. Salinity is the major water quality factor in the basin and it has interactions which overweigh all other considerations except the availability of the water resource. Man’s uses and control of the water affect salinity as well as flow in the streams. However, it was not possible to demonstrate deleterious effects of salinity in 100-1000 mg/1 range of TDS typically found in the river proper; literature searches have shown effects causing species dominance changes, etc., in higher salinity (>1000 mg/1) in brackish waters and estuarine waters. Also it was not possible to isolate salinity effects from field experience; disappearances of species, productivity changes, etc., could not be related to salinity increases because of confounding by instabilities in flow and substrate, sedimentation effects, flow pattern changes, flow variations, time lag in biological response, and introduced species. Consequently, it was necessary to limit studies to the effects of PL 92-500 in changing the impacts of wastewater treatment plant effluents on water quality parameters, the stream ecosystem, and the basin ecology. The basin is marked by large area and a low population (three persons per square mile) excepting the three metropolitan areas of Phoenix, Tucson, and Las Vegas. Industry and large communities are sparse as is the water supply. The development of energy resources may have significant impacts on population, hence waste discharges. To analyze PL 92-500 impacts on the Colorado River it was necessary to isolate a study area which typified the major problems but did not represent necessarily the entire basin, i.e. low population, high salinity, and high potential energy for development. The area chosen was called the Green River Reach Study area and extended from Jensen, Utah to Green River City, Utah, and all the tributaries to that reach. It was assumed that as a result of the existence of PL 92-500 and its goals that industry and especially the energy industry will attempt to prevent any flow discharge to minimize the effects of flow discharge requirement changes with changing technology. A stream model was used to assess loadings from six major communities (the largest was Price at 6218 population) in the study area under projected population increase with no energy development (OBERS E) and with high energy development for four time periods and treatments, 1977, 1983, 1985, 200, and BPT (Best Practicable Technology), BAT (Best Available Technology), and EOD (Elimination of Discharge, “zero discharge”). The results of analyzing loadings effects on DO (Dissolved Oxygen), BOD (Biochemical Oxygen Demand), coliform, and suspended solids in the streams indicated that minimal effects of PL 92-500 on water quality can be expected. Diffuse sources of pollutants and minimal stream flows are more significant. It is reasonable to expect that this is true throughout the greater portion of the Colorado River Basin.