EXPERIENCE WITH SELF-DREDGING HARBOUR ENTRANCES

P. Donnelly, I. MacInnis

Abstract


About 7 years ago, the Department of Public Works of Canada requested the assistance of the National Research Council to devise a means of reducing sediment deposition in the entrance to a small harbour at Dmgwall, Nova Scotia. Siltation of this harbour entrance, which opens to the Atlantic, was so severe that on occasions it was completely blocked by sand at low tides. The desired objective was to devise a layout of structures which would maintain an entrance depth of 12 feet at low tide. Model studies were carried out and a breakwater configuration was evolved which appeared to have some "selfdredging" characteristics. The recommended structures were built in 1962 and to date have been successful in maintaining minimum depths of 5 feet at low tide which is adequate for the fishing fleet using the harbour. While falling somewhat short of the original objective this performance has been very satisfactory when compared with the conditions which existed before construction. Similar installations have since been built at two other locations in Nova Scotia Which are on the Gulf of St. Lawrence. Indications so far are that similarly satisfactory results have been obtained. This paper describes the installations, makes some tentative suggestions concerning the mechanisms involved m their operation and provides data on their performance.

Keywords


self dredging; harbor entrances

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