| Citation |
Jordan, P., Gluns, D., Covert, A., Curran, M. (2007) Sitkum Creek Fire, 2007, N70347 Post-Wildfire Risk Analysis, BC Ministry of Forests and Range. Prepared for BC Ministry of Forests and Range: Southeast Fire Centre, Southern Interior Forest Region, and Kootenay Lake Forest District. |
| Abstract/Description or Keywords |
The Sitkum Creek fire burned an extensive area in the upper portion of the Sitkum Creek drainage. The fire perimeter totals 39% of the watershed; areas of high and moderate vegetation burn severity cover 10 and 11% of the watershed respectively. High soil burn severity and water repellency are widespread in some areas, although not as abundant as in some other fires. Some small tributary drainages have high vegetation burn severity in up to 50% of their drainage area. The most likely hazards to occur in the first 3 to 5 years following the fire are: increased streamflow from the burned area, especially during high-intensity summer rainstorms and longduration fall rainstorms; soil erosion from the burned area; and debris flows in tributary streams. Possible debris flows in tributaries T1 and T2 have the potential to cause a debris flood in the main channel of Sitkum Creek, if they were to occur during a time of peak discharge, or temporarily block the flow of the main creek. Sitkum Creek is a community watershed, and its fan is heavily developed. There are high risks to houses and the highway from flooding, debris floods, and possible avulsion of the creek channel. The risk of water quality impacts due to sedimentation of the creek is also high. The following recommendations are made: 1. Information on the post-wildfire hazards and risks should be communicated to stakeholders, including local residents, landowners, and owners of the mine. 2. The 1990 study on alluvial fan hazards should be updated, to reflect changed hydrologic conditions in the watershed, as recommended by the authors. This should include further study and recommendations (if appropriate) on the return periods of floods on the Sitkum Creek fan, the capacity of the present channel and highway bridge to pass these floods and the associated debris, investigation of possible protective works or other improvement on the fan, and flood preparedness. 3. Mitigation treatments, such as aerial mulching, should be considered in the tributary watersheds of T1 and T2, to reduce the debris flow hazard in these drainages. 4. Deactivation of the Sitkum-Alpine road, from the bridge to the mine, should take place, to reduce the hazard of stream sedimentation due to debris flow or erosion events. (It is our understanding that deactivation prescriptions have been completed, and that work will begin soon.) 5. Reforestation should be considered as a treatment to promote hydrologic recovery in the burned areas. 6. A comprehensive watershed risk mitigation and restoration plan should be developed, including a communications plan, to ensure coordination of activities. 7. Consideration should be given to applying hydrologic models to assess the post-wildfire hydrologic changes to Sitkum Creek, and to produce better estimates of probable streamflow. 8. Streamflow and water quality on Sitkum Creek should be monitored for several years, or until substantial recovery of hydrologic processes in the watershed have occurred. Real-time monitoring of discharge should be considered, to assist in forecasting the occurrence of damaging floods. 9. The mill site and mine waste should be inspected for possible sources of contamination that might be affected by the fire or by post-wildfire flooding. 10. Burn severity mapping based on pre- and post-wildfire Landsat imagery should be completed. (This is now underway.) 11. Acquisition of high-resolution satellite imagery, or aerial photography, should be considered, to facilitate planning of reforestation or other rehabilitation activities in the watershed, and to facilitate monitoring of post-wildfire erosion events and recovery. 12. Rainfall, erosion events, revegetation, and the effectiveness of any mitigation treatments in the burned area should be monitored for several years, to assist with assessment or risks on the fan, and to improve our understanding of post-wildfire hydrologic processes. |
