An emergency spillway with a capacity of 1840 m3/s has been built to increase the spillway capacity of the 30-year-old Bearspaw Development so that it can safely pass the probable maximum flood. A unique aspect of the free-overflow, side-channel emergency spillway is the weir. This consists of an earthfill dyke with a cap and downstream facing of reinforced concrete. Comprehensive hydraulic model testing was undertaken to provide detailed design data and optimize the design of the emergency spillway. The overflow weir substructure is a zoned earthfill dyke with a 2 mm thick polyethylene membrane at the top of the impervious core to prevent frost heave of the concrete lining. The reinforced concrete lining of the spillway is required for erosion protection and is designed to withstand the hydrodynamic drag and uplift forces caused by flowing water as well as piezometric uplift pressures due to seepage. An extensive underdrainage system was installed to reduce uplift pressures under the lining. An unlined return channel excavated through overburden and rock conducts spill way discharges back to the river. This paper describes the model testing, design, and construction of the emergency spillway. Key words: spillway, overflow, weir, erosion, drainage, hydrodynamic, frost heave, membrane, revetment, model testing.
The design and construction of water impounding plugs using sprayed concrete