Title

The Influence of Ice on Channel Morphology of the Kuparuk River, Alaska

Publication Date

12-2002

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Geophysics

Department

Geosciences

Major Advisor

James P. McNamara

Abstract

An F-test on hydraulic geometry data from the Kuparuk River shows that bankfull channel cross-sectional area (Axsec) increases with contributing drainage area (Ada) by one power function at low values of Ada; a "shift" then separates a second power function which best fits the data at larger Ada. Bedload grain-size distributions and downstream hydraulic geometry analysis show changes spatially consistent with the "shift" in Axsec. Basic river controls such as geology and topography do not exhibit obvious controls on Kuparuk River along this critical reach. I investigate the "shift" in Axsec as an erosional affect of in-channel ice types (bed and cap ice) during annual snowmelt. Bed ice occurs in solidly frozen river reaches. During snowmelt bed ice prevents contact between river flows and channel materials, suppressing erosion. Cap ice occurs in deeper sections of the river as a surface layer of ice. Cap ice exposes channel material to snowmelt flows and causes bank scour as it is carried downstream. Using ground-penetrating radar (GPR) and degree-day ice modeling, I determine the location of the transition from bed to cap ice along the Kuparuk River. This transition occurs along the critical reach showing changes in Axsec, bedload grain-size distributions, and downstream river adjustment. The lack of apparent geologic and topographic influences along this reach indicates that ice is causing the anomalous channel morphology of the Kuparuk River.

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