| Abstract/Description or Keywords |
Mess Creek is a large, remote watershed located approximately 140 km southwest of Dease Lake in northwestern British Columbia. The watershed drains 2,306 km2 of the Coast Mountains and Stikine Plateau before joining the Stikine River. Glaciers and glacial outwash channels dominate many of the high-elevation, mountainous headwater reaches of the watershed and these deliver relatively large volumes of sediment to the mainstem channel. Mess Creek is laterally unstable along some channel reaches and often flows in an irregular wandering or anastomosing channel pattern. Avulsions are common along the floodplain, and the channel has experienced major flow path changes. Mess Creek hosts a variety of fish species and thus the whole river and its floodplain are considered fish habitat as per the Fisheries Act. Copper Fox Metals Inc. (Copper Fox) has proposed construction of a haul-road (including a causeway and bridge crossings) along the upper 30-35 km of Mess Creek (above Mess Lake). Selecting the most stable location along the river and floodplain for the causeway and bridges will help minimize any potential disturbance to fish habitat and allow the river to naturally change course over time (in less stable areas). This will also minimize future maintenance costs by reducing potential erosion of the causeway following lateral river migration and adjustment. The morphological character, stability and associated erosion hazard of upper Mess Creek was assessed from both historical airphoto and field investigations. The assessment included approximately 40 km of mainstem river channel extending from the outlet of the study area to the headwater reaches of the watershed and adjacent to the proposed haul-road. An overview airphoto assessment was undertaken for the entire mainstem length of channel, while the channel migration hazard was mapped for two separate 5 km sections of river (10 km in total), each centered near one of two proposed channel crossings. In general, the two proposed channel crossings investigated in this report occur over relatively stable channel types. However, channel change and lateral adjustment is expected in these reaches, and the channel migration hazard has been mapped in the vicinity of the proposed crossings. The channel migration hazard was based on separate assessments of the bank erosion hazard and the avulsion hazard. The bank erosion hazard was assessed by measuring both the rate and spatial distribution of bank erosion across the floodplain or valley bottom, while the avulsion hazard was assessed by delineating the width of the meander belt and considering the past location(s) of a given channel on the floodplain. |
