The Lower Fraser River 2D Flood Model projects the extent, depth, and velocity of water in the Lower Fraser River channel and on the floodplain (which is normally dry land) for floods of different sizes. The model covers a 170 km stretch of the Fraser River from Hope to the Salish Sea (Strait of Georgia). The model can also be used to show dike breach scenarios and the impact of possible flood mitigation options.
For this project in Phase 2 of the LMFMS, 27 flood scenarios were produced. Three simplified maps were developed, and 24 scenarios were simulated by the flood model: 14 base run scenarios (2 with simplified maps only); 8 dike breach scenarios; and 5 scenarios on the effects of different flood mitigation options (four of the five options were modelled).
Some of the model findings include:
- Many areas not currently protected by dikes will be flooded by even a relatively small flood event, and the potential extent and depth of flooding in these areas increases with climate change.
- The total area of floodplain flooded, and number of dikes overtopped increases significantly as the freshet flood scenarios become more severe.
- Setting back new dikes from their current location to create more “room for the river” in flood events may also reduce flood levels in some locations.
- The river channel will undergo substantial change over time as it adjusts to the new, climate change-driven flow regime. There is uncertainty in projecting specific flood water levels, but flood water levels are expected to increase substantially in the future.
- Due to sea level rise, the “transition point” between coastal- and river-dominated flooding will likely shift upstream.
One of the primary objectives of the LMFMS flood modelling and mapping project was to support planning and decision-making related to various flood mitigation options. By simulating mitigation options in the model, their effectiveness can be assessed, and promising options selected for further investigation. Flood mapping information and data will be used to determine a community’s (and region’s) vulnerabilities to multiple flooding scenarios, which can in turn, inform a roadmap for action, including specific mitigation projects. The flood model and maps provide evidence on the nature, extent and distribution of flood hazards and risks across the region, as well as a compelling rationale to take action.