Operating Guidelines

Operating Objectives

The Portage Diversion will be operated to meet these objectives:

  1. To provide maximum benefits to the City of Winnipeg and areas along the Assiniboine River downstream of Portage la Prairie.
  2. To minimize ice jams forming along the Lower Assiniboine River.
  3. Not to increase the water level in Lake Manitoba beyond the maximum regulated level of 247.763 m (812.87 feet) (247.76m), if possible.
  4. Prevent overtopping of the failsafe section in the Portage Diversion, if possible.

Operation Guidelines

  1. Except as provided under Guideline 8, the Portage Diversion shall be utilized to its maximum capability to keep water levels in Winnipeg below 5.18 m (17.0 ft), James Avenue Datum.
  2. The flow in the Diversion shall not be allowed to exceed 708 cms (25,000 cfs).
  3. If flow forecasts indicate that the peak inflow into the reservoir to be 566 cms (20,000 cfs) or more, the Diversion will be put into use as soon as possible to flush out snow blockages and in situ ice.
  4. During the period that there is ice on the reservoir, the water level of the reservoir will not be allowed to exceed 263.65 m (865.0 ft) to provide room for releases from breaching of upstream ice jams.
  5. The conduits of the Spillway structure shall be closed while there is water going over the bascule gates.
  6. While there is ice on the Assiniboine River downstream of Portage la Prairie it is desirable to limit flows to approximately 142 cms (5,000 cfs) in the River if possible. Flows of this magnitude appear to be optimum flows required to assist in flushing the ice down river without causing major ice jams or flooding to adjacent farm lands through local drainage inlets. This procedure provides additional capacity, if required, on the River downstream of Portage la Prairie when the second peak arrives. The level of Lake Manitoba should not be taken into account while there is ice on the Assiniboine River, as the period during which there is ice on the River during spring runoff is only a few days, and diverted flows for this short a period of time have a negligible effect on the level of Lake Manitoba.
  7. After the ice has gone from the Assiniboine River downstream of Portage la Prairie, it is desirable to maintain flows less than 283 cms (10,000 cfs) in the River if possible. Flows greater than 283 cms(10,000 cfs) are above the natural bank stage of the River, and backup of local streams which outlet into the Assiniboine may occur at this level. There also may be seepage problems through the dike, leakage under the dike through gated culverts, and flooding of cultivated land between the dikes.
  8. For flows of up to 850 cms (30,000 cfs) under open water conditions, the failsafe section of the west dike of the Portage Diversion should not be breached if the peak stage in Winnipeg will not exceed 5.49 m (18.0 ft).