Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Civil and Environmental Engineering


Jagath J. Kaluarachchi


Increasing demand on limited water resources calls for more efficient and improved approaches to maximize the benefits of water use. Typically, agricultural water use has the largest share among all water use sectors. Therefore, finding the best agricultural water management alternatives to maximize profit and reduce financial and other related risks under limited water availability is essential. Treated wastewater is an important alternative source of agricultural water which has the potential to reduce the stress on freshwater sources from urban and industrial sectors. Thus, further research on optimal agricultural water management is needed to find the best management alternatives that address profitability and reduce stress on freshwater supplies, and related risks, by considering the potential use of treated wastewater when available. The overall goal of this work is to address this research need through an integrated methodology that uses irrigation, economics, and environmental and public health principles. This dissertation consists of three parts. The analysis in the first part determines the optimal crop pattern that maximizes profit under limited water supply that can be applied at regional scale farming operations. The goal is to find different alternatives of land and crop patterns that increase profit and reduce financial risk of not achieving a given revenue target. The second part extends the work of the first part to include the use of treated wastewater to reduce the stress on freshwater sources while maximizing profitability and minimizing public health and environmental concerns. The third part evaluates the economic benefits and limitations of using treated wastewater for agriculture on the urban and industrial sectors. This part also discusses other alternatives such as desalination that increase the net economic benefits, reduce the price of water, and assesses the needs in the institutional setting to encourage the use of treated wastewater in agriculture. The Bear River Valley of Utah was used as the study area for the first part of the work. The results showed that crop rotation leads to larger risk decrease more than crop monoculture and diversification cropping systems. Thus, alfalfa-wheat rotation has significant risk advantages over monoculture production and diversification cropping because of enhanced yield and price offsetting ability. The second part of the study used data and information from the Gaza Strip, Palestine, to demonstrate the potential use of treated wastewater given the severe water shortage facing this region. The tradeoff analysis from this work showed that profitability and economic efficiency of water use can be increased significantly compared to the existing conditions through the use of treated wastewater. Groundwater extraction in Gaza can be reduced from 57 to 36 million m3 allowing the corresponding areas of groundwater table below mean sea level to decrease from 76 km2 to 32 km2 as a result of using treated wastewater, indicating significant aquifer recovery. The final part of the analysis also used the Gaza Strip as the case study. The results showed that the benefits of using treated wastewater increase over time as demands increase and water becomes scarce, but the economic value of water does not fall below the seawater desalination cost of $0.60/m3. The urban and industrial water prices reduced significantly when wastewater is used for agriculture. Net benefits from treating and using wastewater far exceed the institutional change costs borne by the corresponding institutions. The work conducted by this dissertation clearly showed that new methods of integrated analysis using the concepts of water allocation, irrigation principles, economics, environmental concerns, and public health risk can be successfully conducted to improve existing agricultural water allocation and management practices in water deficit regions. Also such analyses will provide valuable information and insight leading to better management of valuable water resources that increase profitability in agricultural production while reducing stress on freshwater supplies through the use of alternative sources of water.