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Chapter II Description of Alternatives 21 moveable to allow low level withdrawals. The intermediate section extending from elevation 3,450 to elevation 3,550 would be fixed and is not adjustable. The top section extending from elevation 3,550 to elevation 3,650 is moveable to allow high level withdrawals with varying water surface elevations. Support and restraint of the curtain is accomplished with a series of chains, cables, buoys, floatation tanks, and deadweight anchors. The dead weight of the Hypalon curtain is supported by 20-ft-long floatation tanks located at the top of the curtain, When subjected to density and flow loads, the Hypalon curtain would span horizontally to vertical chains spaced on 20- foot centers across the canyon. The vertical chains offer primary support to the curtain and are supported by submerged buoys on the top and dead weight anchors resting on the reservoir bottom. Intermediate support of the vertical chains is provided by cross canyon wire rope cables at elevations 3,450, 3,550, and 3,650. These support cables are anchored to the canyon walls at each end with wedge-type rock anchors. Dead weight lake anchors provide intermediate support to the horizontal cables and breaks them into eight spans of approximately equal lengths. The dead weight of the horizontal cables are supported by 20- ft-long floatation tanks along the entire length of the cables. The 20-ft-long floatation tanks at elevation 3,650 that support the curtain and horizontal cable are variable buoyant tanks. Air can be pumped into the tanks to raise them or the tanks can be flooded to lower them. The horizontal cable at elevation 3650 is shackled to the vertical chains so the elevation of the top of the curtain can be adj usted from elevation 3650 to elevation 3550 by raising and lowering the variable buoyant tanks. The curtain fabric is attached to the tanks by bolting between flat bars welded to the tanks and fiberglass battens enclosed in sleeves in the fabric. The primary purpose of the 20-ft-long floatation tanks at elevation 3,550 and elevation 3,450 is to facilitate construction of the curtain. Initially, these tanks would be full of air and then would be flooded to lower the curtain into position. The tanks would be partially filled with floatation foam to support the tank dead weight. The 20-ft-long floatation tanks at elevation 3,250 are variable buoyant tanks. Air can be pumped into the tanks to raise them or the tanks can be flooded to lower them. This would raise and lower the curtain between elevation 3,250 and 3,450. Half of the variable buoyant tanks would be operated by an air compressor located on the left bank of the reservoir and half of the variable buoyant tanks would be operated by an air compressor located on the right bank of the reservoir. Engine generators are required to provide power for the air compressors. One-inch air hoses would be run between the air compressors and each variable buoyant tank. The large size of the lake anchors prevents them from being installed as a single component. First, a 20-ft x 20-ft steel frame with spikes would be lowered in position; then, four 5-ft x 10-ft x 10-ft blocks of concrete would be lowered into the frames to provide the downward force required to secure the anchor. The mooring line would be wire rope with a heavy chain leader at the anchor to ensure the load is transferred horizontally to the anchor. The weight