Agriculture and Irrigation - Request for Proposal - Bens Lake Diversion Structure Assessment and Hydraulic Study

Background The Bens Lake diversion structure was built in 1978 in conjunction with the Vermillion River flood control works and is located in NW 21-54-13-W4, Central Alberta, west of Two Hills. The main purposes of the structure are to reduce the adverse effects of flooding on agricultural land and provide water level control for the development of more suitable habitat for waterfowl. Diversion Structure The structure acts as a low-level crossing and provides lake level control for Bens Lake and to reduce flood impacts downstream in the Vermilion River by utilizing Bens Lake as off-stream storage capacity during a flood. The structure is located on the Vermillion River immediately downstream of the confluence with the Bens Lake outlet. The structure consists of a 16m steel sheet pile weir with concrete capped gabions. The structure measures approximately 10m in length and 20m in width. Inspections by the operations staff indicate that the structure is in poor condition, AGI requires an assessment of the structure to confirm its condition. The sheet piles in the structure have experienced heaving in the past. The concrete capping on the structure is also cracked, settling and heaving. Water has been observed flowing under the downstream apron and through the gabion baskets. In the winter of 2020, it was noted that the concrete condition had worsened compared to past years. The structure is located on the Vermillion River (53.679857, -111.861293), as such the hydrological impact of removal of the structure compared to replacement needs to be assessed along with the ecological and environmental impact. The surrounding area serves as a habitat for a wide variety of wildlife in the area. The study area should be at minimum upstream of the structure on Vermillion River, including Ben’s Lake and channel, Watts Lake and channel and, and as far upstream as the structure impacts. The study area should also go downstream of the structure on the Vermilion River including impacts on Lake. A previous study was conducted in 2018 where a one-dimensional unsteady hydraulic HEC-RAS model was created to determine the impact of the Morecambe structure on the vermillion river system. AGI is interested in the impact of the Bens Lake structure on Morecambe structure operations. Options for replacement or removal of the structure need to be developed and the impact of the removal of the structure needs to be assessed.