» About Shellmouth Dam | Agreement Objectives

The dam was constructed in the late 1960's to provide flood protection and water supply on the Assiniboine River. The dam is located about 19 kilometres northwest of Russell at the confluence of the Assiniboine and Shell Rivers.

Construction of Shellmouth Dam was completed in 1970. The dam is an earth-fill structure with a reinforced concrete overflow spillway and gated low level outlet. The low level outlet is used for controlled release of day-to-day flows. The spillway discharges major flood flows to the Assiniboine River.

The reservoir created by the dam is known as Lake of the Prairies. It is approximately 35 miles(56 kilometres) long with a storage capacity of 300,000 acre feet (370,000 dam³) at the summer target operating level of 1402.5 feet (427.5 metres). The surface area of water stored in the reservoir at summer target operating level is 13,500 acres (5,500 hectares).

» About Shellmouth Dam | Agreement Objectives

The $8 million Canada-Manitoba Shellmouth Dam Consolidation Agreement was signed in January, 2003. The Agreement objectives are to provide compensation to upstream land owners in Saskatchewan, to acquire additional upstream land in Saskatchewan, to study downstream impacts in Manitoba, and to upgrade the Shellmouth Dam (Lake of the Prairies).

Compensation is being paid upstream in Saskatchewan on lost income to farmers due to seeding delays as a result of reservoir operation. A compensation package is being implemented with respect to past damages, and land control is being obtained to preclude future claims.

Downstream impacts in Manitoba as a result of the operation of the Shellmouth Dam, particularly the reach of river from the dam to Provincial Trunk Highway (PTH) 16, will be studied in detail under this agreement, including costs for mitigation. During scoping investigations residents advised that study of downstream impacts should extend beyond PTH 16.

Water supply enhancement is not needed today on the Assiniboine River, but it is projected that, at some point in the future, demand for water may outstrip supply. For example, the needs of existing vegetable processors, plans for future potato processing plant expansion, establishment of potential ethanol production facilities and requirements for municipal water supply expansion could consume the estimated current unallocated annual water supply of 20,000 acre-feet. It is important to plan for the future to ensure that Manitoba is poised to capture economic growth in the agriculture sector, while at the same time providing flows in the river to maintain water quality and support aquatic life. Therefore, the Agreement calls for upgrading of Shellmouth Dam.

In regards to the dam itself, the proposal calls for the addition of gates to the crest of the spillway to enhance downstream water supply and flood control. Over the past several decades many options for enhancement of Assiniboine River water management have been studied, including the merits of adding gates to the dam. It initially appears that adding gates to the spillway crest of Shellmouth Dam to improve operational flexibility may be the best option. However, a detailed review of past studies and environmental issues associated with a variety of alternatives for Assiniboine River management will be undertaken to determine whether the installation of gates is the best option.

If adding gates to the spillway crest of Shellmouth Dam is selected as the best option, the reservoir would have to be operated at higher levels (possibly up to 6 feet higher for summer target levels) to improve water supply potential. As part of the study, a range of operating scenarios and potential impacts would be studied. It is possible that some existing works on the reservoir would have to be altered as a result of changes to reservoir operation.

The funding agreement calls for project to be completed by March 31, 2006.

Background information on specific issues such as reservoir operational strategies, environmental assessment, public consultation, and others is available by accessing other documents in this website, such as the Q & A, or by contacting the Project Manager directly.