Date of Award:

5-2022

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

L. Niel Allen

Committee

L. Niel Allen

Committee

Jeffery S. Horsburgh

Committee

David K. Stevens

Abstract

Utah is, on average, one of the driest states in the United States, second only to Nevada, and drier conditions are projected. Irrigation is the largest water user in the state, representing about 80% of the total freshwater withdrawn each year. Withdrawals are obtained from sources like reservoirs or streams, or underground water from wells and springs, and supplied for use. The United States Geological Survey, a reputable federal science agency, has provided irrigation freshwater withdrawal estimates every five years since 1950. Understanding what factors affect irrigation withdrawals can better inform water resource planning to reduce withdrawals and conserve surface and groundwater in Utah. Prior studies have found total irrigated acreages, irrigation system technology, and freshwater availability as potential driving factors of these irrigation withdrawal estimates. This study sought to bring these findings up to date specifically in Utah for statewide, sub-state, and county areas. Relationships were assessed using a simple yet robust statistical approach. Statewide results indicate that irrigation withdrawals are not connected with the number of acres that are irrigated, nor with what type of irrigation system is used. This could mean that some practices like fallowing fields, or conversion to sprinkler irrigation systems, may not be sustainable irrigation withdrawal reduction practices. Other significant results, like between annual irrigation withdrawals and May air temperatures, could aid in projecting future irrigation withdrawals in the state. Water year freshwater availability key indicator correlation analyses with annual irrigation freshwater withdrawals showed relatively few significant correlations, suggesting that historical irrigation practices and infrastructure have been adequate at overcoming year-to-year freshwater availability fluctuations. This includes utilizing groundwater stores to sustain irrigation freshwater withdrawals through dry periods, which may be an unsustainable practice if projected drier conditions are realized. Limitations in the analyses were discovered that make it difficult to draw hard conclusions from these findings. There were a wide variety of county results, showcasing the importance and opportunities of localized plans and decision making for sustainable irrigation practices to reduce irrigation withdrawals in Utah.

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