Date of Award:

2007

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geology

Advisor/Chair:

Thomas E. Lachmar

Abstract

Discharge monitoring and water sampling of springs in the southeastern portion of Cache Valley, Utah was performed in order to determine recharge sources and the cause of decreasing flows for some springs. The discharges of 43 springs were measured monthly from May or June of 2005 through March of 2006. Water samples from 36 of these springs plus an additional 10 were analyzed for major ions and trace metals. Twenty-one of the springs were analyzed for deuterium and oxygen-18 and 10 of these were analyzed for tritium. The springs were divided into groups based on when they had their peak discharge. Peak discharges in the summer months suggest recharge from excess irrigation water and/or canal water, whereas peak discharges in winter months suggest recharge from rivers, and peak discharges in spring months suggest recharge by precipitation and/or river water recharge. Multiple discharge peaks suggest multiple recharge sources. The chemical data collected in the study were compared with data from previous investigations to determine potential spring sources, including: shallow ground water, deep ground water, irrigation (river/canal) water, and precipitation. Spring water is characterized by calcium, magnesium, and bicarbonate, similar to deep ground water and river water. However, most of the 21 springs analyzed for deuterium and oxygen-18 displayed an evaporative signature; thus, chemically, the shallow, unconfined aquifer that recharges these springs appears to be recharged in part by excess irrigation water and/or canal water. Several of the springs have high chloride levels indicating the shallow, unconfined aquifer recharging those springs has surface runoff infiltrating into it. Because of the evaporative signature in the stable isotopes, the similarity of major ion and trace metal values, and the discharge trends observed throughout the year, it seems unlikely that the springs are directly connected hydraulically with the deep, confined aquifer, from which most of the wells in the valley withdraw their water. Thus, the recent drought, rather than increased pumping, probably has been responsible for decreases in spring discharges.

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