Date of Award

1993

Degree Type

Thesis

Degree Name

M.Sc.

Department

Civil and Environmental Engineering

First Advisor

Thomas, R.,

Keywords

Geophysics.

Rights

CC BY-NC-ND 4.0

Abstract

The St. Clair River delta, the largest in the Great Lakes, is located astride the border between Michigan, U.S.A. and Ontario, Canada. It resembles a classic river-dominated delta system, with a typical 'bird's foot' morphology. Sediment deposition occurs in levee deposits adjacent to the main channels and in flood deposits via crevasse splays in the interdistributary regions. Anomalous features, such as distributary channels of greater depth than the receiving lake basin, suggest that the origin and growth of the delta do not conform to traditional depositional models. An acoustic array was used to map the subsurface structure of the delta and identify related landforms. The array consisted of side-scan sonar, coupled to a depth sounder and a global positioning receiver. Chenal Ecarte, Bassett and Johnston Channels were surveyed on the Canadian side of the delta, along 48 traverses run both parallel and transverse to the flow direction. The data suggests a model for the evolution of the delta and its progradation into Lake St. Clair, that is termed the 'burrowing-delta' model. Critical to the model is the temperature differential existing between the waters of the St. Clair River from deep Lake Huron and of shallow Lake St. Clair. The river water is cooler and denser than the warmer lake water. At the channel-lake interface, the cross-sectional area of the channel is progressively restricted, thus cooler water is forced to move upslope to lake bed level at an increasing velocity and a dense, fast-flowing underflow current is formed on the lake bed. The current then erodes the lake bed, and a narrow underflow notch is progressively etched across the lake sediments. Downward and lateral erosion of the lake bed continues until a stable channel depth is reached while the notch is extended further into Lake St. Clair. The traction bedload is carried up to the lake bed and then laterally to lengthen and expand the pre-existing levee deposits. The eroded clays of the lake bed are carried into the lake with the distributary outflow, where they are circulated by wind-induced lake currents. Delta progradation is determined by the propagation direction of the underflow notch channel.Dept. of Geology and Geological Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1993 .C44. Source: Masters Abstracts International, Volume: 32-06, page: 1611. Advisers: R. Thomas; D. Symons. Thesis (M.Sc.)--University of Windsor (Canada), 1993.

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