Morphology of the 8-Mile Channel Lake Winnipeg Regulation Project

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Gill, David George
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The Lake Winnipeg Regulation Project calls for the dredging of the 8-Mile Channel, a large diversion channel at the north end of Lake Winnipeg. The entrance of this channel passes through a high sand ridge, which may present difficulties in precise assessment of future hydraulic performance. The prediction of the depth-discharge relationship is difficult to ascertain, and this aspect is studied in some detail. Active fluvial processes produce changes in channel morphology and possible increases in channel roughness values. Most reasonable depths for expected flow conditions are obtained. This aspect was studied by utilizing accepted depth-discharge prediction techniques, and a hydraulic model. It appears that bedforms will not fully develop in the lower reaches of the channel, and from this the assumed design roughness value of n = 0.025 appears reasonable. Sand removal, and bed movement from the channel entrance were studied with the aid of a large hydraulic model; recommendations for the construction of rock-filled dykes or slope cuts to alleviate this bed material movement are present. The alignment of the channel entrance was controlled by rock outcroppings within Playgreen Lake, and this alignment was found to propogate meander tendencies in the lower reaches of the channel. This meandering will probably initiate bank carving in the downstream portion of the channel. Channelization and stabilization by rock removal and spur dyke construction were also studied with the aid of the model, and recommendations are made to control channel meander initiation resulting from the alignment of the channel.