A delta plain sheet sand in the Fraser River delta, British Columbia, Canada

Abstract

Borehole data in the Fraser River delta demonstrate that a nearly continuous sand unit, generally 8 to 20 m thick, underlies the surficial silts and sands of most of the delta plain. The sand unit consists of one or more sharp-based fining-upward sequences and is interpreted to be a complex of distributary channel deposits. Distributary channel migration and the resulting accumulation of channel sands has occurred primarily in a tidal flat environment, due to the interaction of tidal and fluvial processes and the high proportion of sand in the sediment load. This sand unit thus provides a model for sand-rich, river and tide dominated delta plains. Jetties now maintain the position of the Main Channel of the Fraser River where it crosses the tidal flats, and prevent channel migration and further storage of sand in the lower delta plain. As a result, more of the available sand is being transported directly to the river mouth, where failures transport the sand downslope. Consequently, these structures contribute to instability at the river mouth.