Local Geography

Local Geography

Excerpts from The Problem with the Fraser River, Dr. Mike Church: The Fraser River drains 250 000 km2 of south-central British Columbia, mostly mountains and high plateaus that accumulate a significant winter snowpack. Consequently, there is a significant spring snowmelt freshet every year. Annual peak flood flows are of order 10 000 cubic meters per second in the lower river. In the natural, pre-development state these flows covered extensive portions of the floodplain of the river every spring in the Fraser Valley.

Important modifications have included cutting off side channels and the elimination of floodwater storage areas on the floodplain and in the former Sumas Lake (drained in 1928). This has raised floodwater levels within the remaining channel zone above their natural (unconfined) limits and potentially increased the rate of rise of the river bed because water and sediment are confined within the restricted area.

Gravel deposition and lateral movements of the river channel have created a complex of islands, bars and secondary channels in the river between Laidlaw and Sumas Mountain. These features form aquatic and riparian habitat of exceptionally high quality that supports an abundant fishery. The natural shifting of the channel renews habitat at a rate to which the river fauna successfully adapt.

Habitat renewal is an essential process for the maintenance of habitat quality. The ecological wealth of the Fraser River in the gravel reach – which contributes substantial economic value through various fisheries and is a culturally and economically significant aspect of First Nations2 society – is sustained by the gravel transport and the consequent natural shifting of the river channel.

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