Dam breach and inundation mapping studies for Minnewanka and Bighorn dams were undertaken to:
- Re-implement, update and verify numeric modelling and hydraulic flood routing for a fair weather breach,
- Develop digital flood inundation mapping illustrating modeled extents of inundation,
- Assess implications of using digital mapping data and processes compared with previous modelling and mapping results.
The studies were undertaken with a view to the development and refinement of modelling and mapping procedures that could be utilized to assess breach and inundation conditions for other TransAlta structures, or for the same system with newer or more accurate topographic information.
Minnewanka Dam, located north of the Town of Banff is a 35 m high earthfill dam that impounds Minnewanka Lake and forms part of the Cascade Hydroelectric Development operated by TransAlta.
Bighorn Main Dam, located about 30 kilometres southwest of Nordegg, Alberta, is a 90 m high earthfill dam that impounds Abraham Lake and forms part of the Bighorn Hydroelectric Development operated by TransAlta.
Due to the significant outflow hydrographs plausible for a breach of Minnewanka Dam and Bighorn Dam, the entire 740 km and 704 km long river reaches downstream of the structures to the Saskatchewan border were included within the study reach.
The floodway for Minnewanka Dam included the Cascade River below the dam, the Bow River below Banff and reaches of the Oldman and South Saskatchewan Rivers downstream. Mapping included river reaches through Banff, Canmore and Calgary.
Modelling for Minnewanka Dam included the cascading failure effects of six significant dams within the study reach that would be impacted by the breach outflow, as well as the bifurcation of flow into separate floodways along Whiskey Creek and the Cascade River near Banff.
There are no major structures downstream of Bighorn Main Dam to the Saskatchewan border that affected the routing. Mapping included the river reach through Edmonton.
Hydraulic routing and water levels were based on one-dimensional finite difference solutions of the energy, momentum and continuity equations, with fixed bed and banks within the BOSS International DAMBRK software.