Morphology and genesis of deep scour holes in the Mackenzie Delta

Abstract

A unique feature that has been detected in the course of past morphological studies of Mackenzie delta channels, and which is of particular concern to the design of pipeline crossings, is the frequent occurrence of very deep scour holes. A recent survey along East Channel revealed many additional holes, with maximum depths ranging from 13 to 37 m. Using the results of recent and past surveys, an inventory of known scour holes and associated morphological parameters is developed. Most holes occur near bends, and often next to recesses in the channel boundaries, known as scour bays. It is shown that presence of scour bays indicates deeper-than-expected holes while repeat surveys of three holes indicate stability. Previously postulated formative mechanisms of bay-associated holes are critically examined; scour under ice jams is eliminated while lake capture is considered likely. Practical implications of the present findings are discussed and research needs outlined.