Research Document - 2014/029

Hydrological factors affecting spatial and temporal fate of sediment in association with stream crossings of the Mackenzie Gas Pipeline

By L. Burge, R. Guthrie, and L. Chaput Desrochers

Abstract

This paper provides a review of processes involved in the transport and deposition of river sediment as the foundation for the development of a sedimentation algorithm to be incorporated into the Fisheries Risk Assessment Tool (FRAT). The FRAT contains algorithms for sediment entering stream channels due to natural processes and pipeline construction activities. The fate of sediment once it enters stream channels is not part of the current version of the FRAT. Sedimentation may be investigated in one of two ways: a forward physical approach or an inverse morphological approach. The first involves using known physics to predict sedimentation. The second is an inverse approach that uses the observed properties of the stream channel to infer sediment transport and depositional processes. This paper first reviews the forward physical approach through the introduction of the energy terms that are known to drive sediment transport and the terms that resist entrainment. Sediment in rivers is transported in two modes: as bedload and as suspended load. Bedload is coarse material and is defined as the material that moves in contact with the bed. No universally applied bedload transport function exists after more than one hundred years of research. However, a number of approaches to bedload transport have been investigated and are introduced. Suspended sediment is defined as the material that is transported within the water column. Fundamentally, deposition of suspended sediment occurs when the fall velocity of the sediment is greater than the turbulent eddies suspending the sediment within the water column. The inverse approach, using channel morphology to provide information on the antecedent condition of the channel is discussed along with a description of channel patterns. Literature on sedimentation related to pipeline construction and the fate of sediment introduced to northern rivers are introduced. The final section discusses measurable variables for the development of a sedimentation algorithm.

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