Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Engineering and Technology Education


Gary P. Merkley


Two computational models, including several calculation and analysis submodels, were developed to create a tool for assessing the impact of different treated wastewater reuse options on irrigated agriculture. The models consider various aspects of treated wastewater availability (past, present, and future), wastewater quality, agricultural water demand, and the economics of conveying wastewater from treatment plants to farms. The two models were implemented using Visual BASIC.NET in a GIS environment to facilitate visualization of some of the features of an area under study, and to provide a convenient interface for user application. One of the models is for treated wastewater availability calculations, and the other is for wastewater reuse. The water availability model has sub-models including urban population predictions, agricultural land use changes, residential water demand, agricultural water demand (evapotranspiration) for over 40 crop types, and treated wastewater analysis. The water reuse model is composed of three sub-models, including soil water and salt balance calculations, nutrient calculations, and pumping and conveyance costs calculations. The nutrient calculationssub-model is based on an existing model, but was completely rewritten and modified in some parts to accommodate the needs and features of the water reuse model presented herein. A sample application of the models is presented for Cache Valley, Utah. The results show a comparison of treated wastewater reuse schemes for the study area, highlighting how irrigated agriculture would best benefit from the total or partial use of treated wastewater. Two wastewater reuse scenarios were considered. The water availability model shows good agreement with other sources of information in terms of population forecast and calculation of future residential and agricultural water demand. However, according to the results from the model, the rate of increase of the urban area was much higher than the rate of decrease of the agricultural areas between the years 1992 and 2001.The future population growth and water demand increases for urban areas was calculated and validated for Logan City. Also, in the case study the model was shown to be a good tool for wastewater influent analysis for Logan City.

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