| Abstract/Description or Keywords |
Elk River drains a long narrow north-south oriented basin in the Rocky Mountains, with peaks up to 3,300 m in the north and 2,200 m in the south, and has a drainage area of 3,110 km2 at Fernie (Obedkoff 1998, SRK 1995 and Nichols 1988). The river, with an average slope of 0.6 percent, bisects the basin forming a valley 1 to 6 km wide with an elevation of 1,700 m at the source and 750 m at the mouth of Lake Koocanusa, 15 km south of Elko, B.C. The hydrologic regime of Elk River is dictated by snowmelt giving rise to annual maximum flows in May or June. In the study reach at City of Fernie, the river has an irregularly wandering gravel-bed channel, with mid-channel islands and gravel-bars. Historically, the channel has exhibited both lateral and vertical instability. Much of the basin is forested, with some farming in the valley bottom and coal mining, primarily on the east side of the valley. Recreation and tourism are growing industries in the area, and with this – increased development and related issues. Understandably, most easily developed lands are located on the wide floodplain areas that can be subject to potential river flooding and erosion hazards, hence the development of local floodplain management bylaws. The city, established in 1904, is located along the banks of Elk River and is partly protected by dikes constructed in 1983. Sections of the City are prone to flooding and historic flooding occurred in 1948 and more recently in 1995. Other high flow years were 1956, 1972 and 1974. In 1975, the provincial Ministry of Environment (MOE) prepared floodplain mapping for the area, covering roughly a 30 km long reach of the river, centred at Fernie. The purpose of the mapping was to delineate the limits of the 200-year floodplain and display Flood Construction Levels (FCL). Since the time of the mapping, the river and floodplain have changed from natural and anthropogenic factors. Considering the development potential of lands not currently protected by dikes and issues regarding standard and non-standard flood protection works, the City of Fernie wished to address potential flood hazards associated with the Elk River floodplain within its jurisdiction. In May 2005, northwest hydraulic consultants (nhc) was retained by City of Fernie to review the current state of dikes and Elk River flood hydraulics at Fernie. The flood hazard assessment included updating flood profiles, providing comments on existing dikes/bank protection and recommending upgrades to protect existing and potential developments within the city. The scope and terms of reference are attached as Appendix A and provide an overview of the general objectives and goals of the study. City of Fernie staff met with nhc in early June 2005 to discuss the study and provide relevant background information. On the basis of this meeting, nhc developed a detailed work plan to meet the objectives of the study. The work program was broken into the following five components: 1. Elk River hydrology was reviewed and analyzed – including previous reports and recent data – in order to confirm estimates of the design flood flows for Elk River at Fernie (as described in Chapter 2). 2. Reach and local-level geomorphic conditions were analyzed to determine long term fluvial changes that could affect flood and erosion hazard potential along the river (as described in Chapter 3). 3. A HEC-RAS hydraulic model was developed to simulate flood profiles based on survey data collected by City of Fernie in 2005 (as described in Chapter 4). 4. The riverbanks and dikes along the Elk River were inspected to provide information for hydraulic modelling, and to determine potential sites of bank erosion and localized flood hazards (as described in Chapter 5). 5. Finally, a detailed flood hazard assessment was prepared that examines risks of flooding / erosion and outlines viable mitigation options and approximate associated costs (as described in Chapter 6). Conclusions and recommendations of the study are presented in Chapter 7 and provide answers to the fundamental questions posed by City of Fernie in the study terms of reference. |
