Colloque

The stability and erodibility of sub-littoral sediments from Manitounuk Sound

Carl L. Amos

T.F. Sutherland

Membre a labase

Carl L. Amos

Résumé du colloque

A series of fifteen Sea Carousel deployments were undertaken along the length of Manitounuk Sound, Hudson Bay. The results of these deployments show that seabed measurements can be subdivided into three groups on the basis of their response to an applied bedload shear stress: (1) high erosion rates and low resistance to erosion, and (2) low erosion rates and high resistance to erosion. The two groups segregate into distinct morphological regions. Group 1 is found in the inner and central Sound, whereas group 2 is diagnostic of glaciolacustrine and glaciomarine sediments that crop out at the flanks of the Sound. These differences notwithstanding, the erosion threshold and friction angle show a systematic increase seawards along the length of the Sound. This trend is commensurate with a decreasing sedimentation rate, evident from the thickness of the Holocene sequence seen in seismic section. Measured erosion rates show two major types: Type I - a surface phenomenon; erosion is greatest for the first 60 seconds of stress onset and thereafter decreases; and Type II - episodically decaying fashion over a 5-minute period; and type III erosion - continuous erosion. Peak erosion rate shows no relationship to applied bed shear stress. This relationship is valid and consistent for all stations and all erosion types. The tests of this study provide data on three important parameters in the evaluation of seabed erodibility by fluid stresses: (1) the surface critical shear stress for the onset of erosion; (2) the distribution of the critical shear stress with depth below the mudline; and (3) the erosion rate once critical shear stress has been exceeded.