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The use of air bubblers to prevent shoaling at wharves in navigable rivers Ages, Alard Berend

Abstract

The Fraser-Surrey Wharf, situated on the left bank of the Main Arm of the Fraser River just downstream of New Westminster, B.C., has been subject to severe shoaling during annual freshets, ever since its construction in 1926. This has seriously hampered shipping and caused a loss in revenue. In the summer of 1965, Professor E. S. Pretious of the Civil Engineering Department, the University of British Columbia, was approached by the Fraser River Harbour Commissioners (owners of the wharf) to investigate the feasibility of employing air-bubblers to prevent shoaling in the approaches to the wharf. The project study was chosen as a thesis topic by the author, under the supervision of Professor Pretious. The research which was subsequently undertaken involved the theory underlying the interaction between air-bubbles and water; laboratory experiments to measure upward water velocities induced by rising air-bubbles; settling velocities of the bed-sand found in front of the wharf, and the critical tractive shear stresses for impending motion of the bed material. In the field, the hydraulic slopes of the water surface at the wharf was measured to determine if the conditions for bed-load movement existed; river current velocities were measured (surface and sub-surface); weekly, controlled, sounding surveys were carried out in addition to a number of sediment sampling surveys and float studies, to determine flow patterns. Bubbler hoses were designed and prepared in the Hydraulics Laboratory of the University of British Columbia and subsequently installed at the wharf. They were kept operating throughout the major part of the 1966 freshet (May, June, July). Recommendations for improved designs and further research are also made.

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