| Abstract/Description or Keywords |
This report provides the Regional District of East Kootenay (RDEK) with Phase 1 of a regional flood hazard assessment and flood management plan. The ultimate goal of a regional flood management plan is to reduce flood-related damage and cost of mitigation through residual risk reduction planning. The study area spans the entire RDEK, encompassing Electoral Areas A, B, C, E, F, and G; the Districts of Elkford, Invermere and Sparwood; the Cities of Fernie, Cranbrook, and Kimberley; and the Villages of Canal Flats and Radium Hot Springs. This report provides a flood hazard study that prioritizes previously identified flood hazard areas, describes potential effects of projected climate change on flood hazards, and outlines a framework to implement a regional flood management plan. Flood hazard information previously compiled by the provincial government includes 214 separate hazard areas (polygons) totalling 222 km2. This list of hazard areas is likely not exhaustive. Elements at risk inventoried within these areas include property parcels containing buildings, critical facilities (fire stations, police stations, hospitals, and schools), roads, highways, utility systems (railways, pipelines, transmission lines), presence of First Nations reserves, and sensitive habitat (fish bearing streams, known locations of rare species and endangered ecosystems). Approximately $2.4 billion of building infrastructure, or about 36% of the total assessed value of improvements within the RDEK, is located on parcels within or intersecting the inventoried flood hazard areas. This value can be interpreted as an approximation of potential total loss for all flood scenarios within the RDEK. However, it is not an estimate of direct building damage costs to parcel improvements during any particular flood scenario. Given uncertainties associated with hazard area extents, water depths and building locations and that every flood hazard area in the RDEK will not be inundated during a single event, the actual value of specific buildings exposed to flood hazard and the damage sustained during a particular flood event will necessarily be lower. BGC ranked the relative priority of each hazard area using priority scores ranging from 0 to 110 (110 being highest priority). Table E-1 summarizes the number of flood hazard areas categorized at each priority level, organized by Electoral Area. Table E-2 is identical but is organized by community. These results can form the basis to select hazard areas for further analyses and flood management planning at future project phases. Climate Change Impacts on Flood Regimes: Global and regional climates are now changing on time scales commensurate with the design life of many engineering and land use projects. An important aspect of the Phase 1 study was to determine potential impacts of climate change on flood hazards. Climate change will impact flood hazards both directly and indirectly through complex feedback mechanisms. This makes it challenging to reliably estimate future flood hazards for the entire spectrum of flood processes, and spatial and temporal scales. In qualitative terms, potential direct impacts of changing flow regimes, due to climate change, on flood hazards depend on the respective watersheds’ hydrological regime and include: _ For nival-dominated hybrid regimes (i.e. spring snowmelt dominates the annual runoff hydrograph, but autumn rain also contributes): extended flood hazard season (later autumn floods and earlier spring floods); increased secondary peak/autumn flow events; increase in number of high flow events through increased frequency of rain-on-snow events (a driving factor); decreasing snow component and increasing rain component resulting in a “flashier” (steeper hydrograph) response to precipitation events (decreased snow storage); _ For nival regimes (i.e. snowmelt dominates the annual hydrograph, and winter flows are minimized): extended spring flood hazard season; decreasing snow component and increasing rain component resulting in a “flashier” (steeper hydrograph) response to rain events (decreased snow storage); development of secondary peak/autumn flow events. _ For glacial regimes (i.e. ice melt dominates the annual hydrograph): less changes to flood hazard in the early stages of warming, but longer term decreased risk of summer flood hazard; increasing likelihood of spring flood hazard, greater inter-annual variability. Potential direct impacts to debris flows could include a higher frequency of occurrence, though not necessarily an increase in magnitude, as a result of increased precipitation intensity. Potential indirect impacts of projected climatic warming on flood hazards could include, but are not limited to: _ Increased debris flow, debris flood and flood activity as a result of increased watershed runoff, erosion, and sediment availability, attributable to: increased frequency of forest fires resulting from longer and warmer summer seasons; late spring snow melt combined with an intensification of localized convective storms that are particularly prevalent at a time where high temperature differences are found between valley bottoms and high alpine areas; or permafrost degradation as a result of increasing mean annual temperatures. _ Increased peak discharge associated with: higher rainfall amounts and rates; more widespread insect infestations and the resulting tree mortality and canopy loss; increased landslide activity; and, the alteration of channel pattern and stability in rivers associated with increased sediment supply from reduced slope stability. _ Reduced effectiveness of existing dikes and flood infrastructure from changes in the geomorphology of creeks and rivers, as a result of changes to streamflow and sediment discharge. Inherent in discussions of climate change is a projection of future conditions. Human factors not necessarily related to climate change, such as watershed development and river management, are dynamic in time and space and can also impact flood hazards. Many of these indirect consequences have been poorly quantified, if at all, and are highly location specific. They should be viewed as general possible effects rather than prescribed forecasts. Going Forward: Flood Management Plan BGC describes a regional flood management plan based on multi-factor management practices where ecological, social and cultural values are considered parallel to economic values. The proposed approach is consistent with provincial best-practice guidelines for flood risk assessments. The flood management plan contains action items that can be implemented in phases by the RDEK, and includes tasks to complete the following work: _ Risk Assessment Site Selection: Selection of specific flood hazard areas for further assessment, based on the results of the analysis in this report. _ Risk Assessment: Analysis of flood risk and estimation of losses for specific flood hazard scenarios (modeled flood inundation events for different return periods) with consideration of climate change (e.g. supplement the use of historical flood records with projections of climate change effects). _ Risk Evaluation and Risk Reduction Planning: Identification of areas where flood risks are not considered tolerable by stakeholders, based on the results of detailed risk assessment, and development of flood risk reduction options. Also provided are recommendations for additional data collection required to complete the remaining project phases, as well as measures to organize and disseminate geospatial data associated with flood risk management. |
