Date of Award:

12-2018

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Advisor/Chair:

Patrick Belmont

Abstract

Changes in the amount of water and sediment that enter a river can change its shape and size. The way that rivers change is affected by a variety of factors, including the size of the sediment in the river, and past changes to the river. The Diamond Fork River in central Utah has been altered by water deliveredfromthe Colorado River system for over a century. Beginning in 1915, water used for irrigation was delivered through a tributary, Sixth Water Creek, with daily summer flows that were much larger than natural flows. This caused drastic change to the rivers, as they became wider and vegetation along the channel margin and floodplain was destroyed. Management changes in 1997 and 2004 reduced the amount of water and sediment added to the river. In this study, we sought to understand how Sixth Water and Diamond Fork changed in the past and what the implications are for the future.

We used data from a variety of sources to describe how and why the river changed in the past. Our results indicate that parts of the river that are not confined by valley walls became very wide during the period of elevated flows and narrowed after the change in management in 1997. Confined reaches experienced minor changes over the period of record. Areas of the channel that were most dynamic in the past are the most susceptible to future change because they have finer sediment that is more easily erodible. Areas that did not experience past changes are unlikely to change in the future without direct intervention from humans or beaver. The findings of this study improve our understanding of Sixth Water and Diamond Fork, and confirm the importance of past changes and valley confinement.

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