Glen Canyon Dam and Powerplant

sources of leakage or discharge to the plant drainage sump for collection and evacuation to the tailrace. Water collected in the sump is automatically pumped to the tailrace by two 1,000-g.p.m. deep-well turbine pumps under float control. Principal water sources considered in the design of the system were leakage from submerged powerplant walls, foundation drains, and mandoors; cooling water discharge from turbine packing boxes and air compressors; blowoff from fire lines, compressed air lines, strainers, and relief valves; oil room sink drain; discharge from sprinkler systems; and backwash drain from possible future domestic water filters. Special features include gravel-filled chilling basins for oil room drains to extinguish possible burning oil, and open discharge from the generator pit drains for visual detection of leakage. Four 24-inch-diameter emergency drainage openings with shutoff and flap valves are provided in the downstream wall of the powerplant to limit flooding to the lower levels in event of a serious plant flooding condition.

The drainage sump is provided with a manually controlled, water-operated eductor for complete evacuation of the sump to facilitate sump cleaning and equipment maintenance. The drainage and unwatering sumps share a common vent to the outside for maintaining atmospheric pressure in the sumps.

(c) Unwatering System.-The purpose of the unwatering system is to drain the draft tube and residual water in the spiral case and horizontal portion of the penstock for inspection or repair of the turbine. The penstock and spiral case will be drained down to tailwater level through the turbine before the unwatering system is used. Pipelines from the spiral case and draft tube conduct the water to the unwatering sump, where it is pumped to the tailrace by two 5,000-g.p.m. deep-well turbine pumps. The design objective is to accomplish the unwatering promptly and with minimum hazard of flooding through misoperation. Principal factors affecting design are tailwater level to be used, volume of the draft tube, volume of the spiral case and penstock below the tailwater level, sump elevations and volume, pump capacity, pipeline size, time to unwater, gate leakage, and conditions existing if the spiral case drain valve is opened by mistake with the penstock under full pressure. The spiral case drain valve should never be opened with the penstock under pressure.

The adopted design provides for unwatering of a unit from tailwater level with the bulkhead gates properly seated and normal leakage occurring. The spiral case drain header is normally closed to the sump