A method of determining runoff from ungaged semi‐arid unit watersheds is presented. The method consists of using the realistic rotating disk rainfall simulator (Rotadisk Rainulator) to measure the infiltration rate combined with data from recording raingages. The infiltration rate is expressed mathematically as a function of rainfall volume and soil parameters by a modified Horton‐type equation. A runoff depth for the unit area is then calculated using a computer program which essentially subtracts the infiltration and surface storage from the rainfall as measured by existing recording rainfall records. The method was tested using four 1‐ac gaged watersheds on the Atterbury Experimental Watershed on the valley floor east of Tucson, Arizona. In general, the measured and calculated runoff were in good correlation, while the standard deviation of the differences between them was between 1 and 3 mm over a 3‐year period for the four unit watersheds tested.

In 1974 and 1975, experiments were conducted near Buckeye, Arizona to study the influence of municipal waste water on the growth and yield of cotton (Gossypium hirsutum L.). Two sources of irrigation water were used: (i) pump water from local wells (control treatment) and (ii) municipal waste water and pump water in a 50:50 mixture.Cotton irrigated with the waste water and pump water mixture grew taller with more vegetative growth than did cotton that was irrigated with pump water alone. When cotton was irrigated with the waste water and pump water mixture, the yields of seed cotton and lint cotton were higher than the yields from cotton irrigated with pump water. Cotton irrigated with waste water and pump water produced lint of the same quality as did cotton irrigated with only pump water.Municipal waste water can be used effectively as a source of irrigation water and plant nutrients in the commercial production of cotton in Arizona and, possibly, in similar environments throughout the world. When municipal waste water is mixed with pump water that is high in total soluble salts, the salt content of the mixture is lowered and the quality of the irrigation water in the study area is improved.

Water utilities, especially smaller ones, are having increasing difficulties proving increased treatment requirements required in the United States for the removal of chemical and microbial contaminates in drinking water. This project sought to evaluate the virus removal potential of combined slow sand filtration and nanofiltration by a pilot plant for application to a small utility which uses a surface water supply. Nanofiltration is a relatively new water treatment technology which has become available since 1986. It is similar to reverse osmosis but has a higher molecular weight cut-off and is less costly to operate. The bacteriophages MS-2 (28 nm) and PRD-1 (65 nm) were seeded into surface water entering a pilot plant and samples collected after sand filtration, nanofiltration, and of the nanofilter reject water. These phages were selected for study because of their small size and poor adsorption to surfaces. The slow sand filter removed 99% of the MS-2 and 99.9% of the PRD-1. There was between a 4 to 6 log reduction of the phages by the nanofilters. PRD-1 was removed to a greater extent than MS-2 by both the sand filter and the nanofilters.

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The influence of municipal waste water on the growth and yield of alfalfa (Medicago sativa L.) was studied in field experiments near Buckeye, Ariz., in 1974 and 1975. The crop was planted in October of each year at a seeding rate of 22.4 kg/ha (20 lb/acre). Approximately 150 cm (60 in) of irrigation water were applied in flood irrigations each year. The response of alfalfa to two irrigation treatments: (i) pump water from local wells (control) and (ii) municipal waste water from Phoenix and pump water in a 50:50 mixture was compared by sampling the first harvest in selected fields. The hay was harvested when 10% of the alfalfa stems had one or more flowers. Alfalfa irrigated with the waste‐water and pump‐water mixture produced taller plants and higher yields of hay than did alfalfa grown with pump water alone. Total protein in the hay and in vitro dry matter disappearance (IVDMD) of the hay was the same for alfalfa grown with both sources of irrigation water. When municipal waste water was mixed with pump water high in total soluble salts, the salt content of the mixture was reduced and the quality of the irrigation water was improved. The higher hay yields obtained when alfalfa was irrigated with the waste‐water and pump‐water mixture than when grown with pump water alone probably resulted from lower concentrations of soluble salts in the water mixture than in the pump water.