of reinforcing steel were used. The greater part of this was in the arch, but a very considerable quantity was used in dowel pins, braces to the gate-tower crossing the surrounding space, as well as in the tower proper and about the gate-house, spillway, and thrust beams; no accurate segregation was made, as all was paid for at one price per pound, regardless of kind or place of use.

THE OUTLET SYSTEM.

The outlet system comprises an intake tunnel, a discharge tunnel, a vertical gate-tower in a shaft and carrying three balanced gates, set at the bottom of the tower and at the one-third and two-thirds points of the height, a sump or water cushion at the bottom of the gate-tower, and a hand-operated device in the gate-house for opening and closing the gates.

The concrete tower carrying the gates has an inside diameter of 6 ft.; the walls are 30 in. thick, and the outside diameter is 11 ft. This gate-tower is set in a shaft, 15 ft. in diameter, blasted out of solid rock up to about Elevation 70 and thence to the top forming a part of the north tangent. The annular space about the tower is always full of water, supplied through the intake tunnel; and, on opening a gate, discharge occurs into the 6-ft. opening in the tower, from which it drops to the sump and is discharged thence to the stream through the outlet tunnel. Leading from the reservoir to the annular space in the shaft about the gate-tower is the intake tunnel, 60 ft. long, with a crosssectional area of 33.8 sq. ft., and with its bottom at the level of the bottom of the lower gate, at Elevation 5, or 145 ft. below the top of

the dam.

The outlet tunnel is also about 60 ft. long, and has a cross-sectional area of 50.2 sq. ft. It is set at a lower elevation than the inlet, and is arranged for a water cushion in the central shaft and a water seal for preventing a draft of air through the gate-tower, thus precluding the formation of ice. This is a matter of importance in this cold place. As it is necessary to draw all water through the old outlet system when the reservoir surface is below Elevation 100, the tunnels were designed to carry only the capacity of the old outlet. It would have been better, perhaps, to have made them larger, in order to avoid excessive velocities with the larger flows possible when the water is higher than the old dam.

THE TRASH-RACK.

The old outlet had been provided with a light steel trash-rack, and, as it had given no trouble during 18 years of use, a similar rack of by 5-in. steel bars, 5 in. from center to center, was placed at the new outlet. The rack rests on four pieces of 90-lb. rails, spanning the shorter way. When the water was drawn off, in the fall of 1917, it was found that trash which had gathered on the rack had reduced the flow of water until the resulting pressure had bent the steel rail supports and bent and twisted the rack bars. It is fortunate that the rack was not stronger; had it been equal to holding the pressure, a very embarrassing situation would have resulted. No indication of the condition was visible, and it was not suspected until the water was drawn off.

The bent and twisted rack was entirely removed, and the channel between the old and new outlets, about 5 by 5 ft., with an open top, was covered with a grill of pine poles having a minimum diameter of 9 in. These poles have an average length of 16 ft., and span the channel in an inclined position, extending from the outer side of the channel to the rock wall of the cliff on the other side, with clear spaces of 6 in. between the poles. The distance covered is 70 ft. The poles are fastened in place by setting 1-in. steel pins in the rock and using ties of No. 9 galvanized wire. This arrangement has not yet been tested, but promises good results.

THE CYLINDRICAL BALANCED GATES.

Each gate works in a cast-iron ring or cylinder set in the concrete walls of the gate-tower. Each cylinder has six 2 by 2-ft. openings in its perimeter, and these are symmetrically spaced. Freely movable vertically inside of the stationary rings are the gates proper, which are cast-iron cylinders with no openings. When the gates are fully down, the openings in the outer cylinders are closed. At the tops and bottoms of the cylinders are fitted heavy rings of naval bronze; when the inclined faces of the bronze come in contact, a water-tight joint is formed.

This arrangement insures a perfect balance of water pressures. Use has demonstrated that no more force is required to operate these gates under pressure from full heads of water than when there is no pressure. Hand-wheels are all that are needed for operation; the arrangement

provided for the purpose works very easily, and with such smoothness and speed as to call for nothing better; power operation would be of no advantage.

There are two stems, of 3-in. cold-rolled steel shafting, rigidly attached to opposite sides of each gate, extending up to the operating gears and below each gate, to form guides to steady them and assist in keeping them in position. The stems of the lower gates pass through holes in the castings of the upper gates, and all are provided with bronze-lined guides every 12.5 ft. in height. The top guides have feather keys, in order to prevent turning, and the bronze linings have a clearance of in. to allow for incrustations. The upper gates, when opened, discharge through the lower gates, and the small projections of stems and guides do not interfere with the discharge.

The tops of the stems are threaded with single square threads, three to the inch, working in heavy bronze nuts with thrust ball-bearings above and below the nuts. The hoists are arranged to operate the two stems of each gate at the same time by using one hand-wheel, having a gearing of cast iron with machine-cut teeth. The stands carrying the gearing are set on a heavy cast-iron ring with brackets, in such a manner as to leave a large opening at the top of the shaft for supplying air to overcome the strong suction caused by the discharging water. The need of this is shown by the fact that, when the gates are discharging, it is very difficult to open the steel door to the gate-house against the air pressure, notwithstanding the generous supply of air through the top ventilator on the gate-house provided for that purpose.

The wisdom of making the stems much heavier than called for by their computed tensile strength is shown by the accidental lodging of a 5-ft. length of 6 by 8-in. timber in the lower gate in some unaccountable manner. An attempt to close the gate showed that something was wrong, for before one man had nearly exerted his full strength on the hand-wheel, the heavy cast-iron top ring was started from its anchorage. When the reservoir was emptied, it was found that the timber was cut at least half way through. Lighter stems could not have withstood such abuse without being damaged.

THE CONCRETE.

The Red Devil brand of cement, manufactured at Devils Slide, Utah, was used throughout. The cement passed the tests satisfactorily,