Water Intake Improvements
Fort Providence, NWT
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Ice opening over intake end location. Drill line is stretched out along the intakes before they are installed. |
| Client: | Department of Municipal and Community Affairs |
| Consultant Contractor: | Dillon Consulting Ltd., Yellowknife |
| General Contractors: | Stan Dean & Sons Ltd., Hay River |
| PWS Project Officer: | Philip Kienholz |
| Construction Cost: | $518,000 |
| Scheduled Completion: | March 2004 |
The old water intake to the treatment plant was through a gravity-fed wet well on the shore of the Mackenzie River. It had problems with low water, silt accumulation, ice damage, and ice build-up preventing access to pumps in winter. The river there has a ten-knot current, and ice jams and pile-ups can force ice down to gouge the river bottom.
Fire-fighting water requirements were predicted to exceed the plant's storage capacity before the plant was to be replaced. A planning study showed it was cheaper to install two intake lines, one for process water and one for fire-fighting water, than to build more storage capacity. The two lines could also act as back-ups for each other.
Design studies mapped the river bottom, evaluated costs and risks of low water and ice thickness, and determined the location for the new intakes. The contractor proposed directional drilling for installation. He drilled from right next to the plant located on top of the river bank, down the bank to a depth of 20' under the river bed, then poked up into the river. This saved $76,000 from the cost of a below-water trench, which would have required steel shielding to protect against ice gouging down to the 2' deep pipe installation. The ends of the intakes have steel sections to resist ice damage, and each intake has double stainless steel screens with a breakaway function. A major ice strike would only break away the first screen, and not tear out a section of the line. The second screen would still be in place.
The work was done during winter. After the drilling was done, the new lines were fabricated on the ice surface, attached to the end of the drill, and the drill pulled the new lines back through the drill holes to the plant.