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pickup of salts within the channel as flows rise and fall. w w w <::> These issues represent some of the more important which must be reviewed in assessing the state-of-the-art of hydrosalinity mod- eling before applying it to evaluate any specific management strategy. Purpose The hydrosalinity models available in the literature vary in the degree of complex- ity used to represent the chemical reactions that occur within the soil-water system. Some models such as those descrihed by Dutt et a1. (1972) are detailed dynamic models which attempt to portray many complex phenomena that occur within the soil-water system including nitrogen transformations. At the other extreme of soil-water-salinity modeling are the steady state TDS models based on the conservation of mass principle formulated by many rese'archers including Terkeltoub and Bahcock (1971). The complex hydrosalinity models need an enormous amount of data, much of which is usually not available in the real world, and large amounts of computer time. The simple models, based on steady-state conditions, require less data but provide less detail. For a particular application, a model must be chosen from an appropriate point within this range. The key issues in the selection are: 1) The reliability, in terms of the de- sired use, of the simpler steady- state models. 2) The additional reliability achieved for the desired use with the complex hydrosalinity models. 3) The possibilities for upgrading a relatively simple hydrosalinity model to predict the impact of management practices on the salin- ity of return flows without having to collect dat~ for the other features models. capable of data. of the more complex This model should be utilizing minimum field The purpose of this research was to assess the state-of-the-art of hydrosalinity modeling in representing the salt pickup process within the soil-groundwater system. The assessment is geared to developing a practical management tool for predicting how the salt outflow from irrigated agriculture is affected by various farm water management practices. Scope In order to achieve the purpose of the study, the research was directed to the following tasks. 1) A review of pertinent hydrosalinity models, soil-water system models, and groundwater models with particu- lar reference to the model capabili- ties in representing the various processes controlling salt and water flows in an irrigation water supply system, assumptions in the models, and modeling gaps, if any. 2) An inventory and analysis of field data from selected irrigated areas so as to have information available for verifying quantitative relation- ships proposed to depict salt pickup mechanisms. 3) The development of a relatively sim- ple hydrosslinity model and a demon- stration application based on cali- bration with field data from se- lected irrigated areas. 4) Demonstrative application of the model to examine the effects of al- ternat i ve i rr igat ion water manage- ment policies on return flows and salt loadings. 2