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of the canyon, but the bottom is covered with bowlders and sand. It seems probable that it is at least 20 to 25 feet to solid rock, but no borings have been made to test this locality.
PROPOSED CURRIER DAM.
The dam at this point as designed is to be of the rock-fill type. The location of the dam and spillway are shown in fig. 20. It is necessary either to excavate a spillway or to build a long wing wall to prevent the flood water from flowing around the end of the dam and over the cliff onto the lower slope. It was decided to excavate a spillway and use the rock in the dam. The dam will have a maximum height of 135 feet above the surface of the stream and will probably extend 20 to 25 feet below to bed rock, as shown in fig. 21. The upstream slope is to be 14 horizontal tol vertical, and the downstream
FIG. 20.—Currier dam site and spillway on Arroyo Seco. slope 14 horizontal to 1 vertical. The top width is to be 20 feet. The extreme length of the dam will be 1,460 feet, but, only the upper 20 feet of the dam will have this length, the balance being less than 500 feet long. The crest of the dam is to be 15 feet above the level of the spillway. In the future, if observations show that it is advisable, the level of the spillway can be easily raised. If raised 5 feet it would increase the capacity of the reservoir about 3,000 acre-feet. The dam is to be made water-tight by a 1:-foot layer of asphaltic concrete, laid on the upstream slope of the dam. This concrete is to be covered with 3.feet of hand-laid rubble to protect it from the heat of the sun and weathering, and is to be of the same composition as that described on page 63 for use at the Foster dam. A cut-off wall of Portlandcement concrete is to be carried down to bed rock at the upstream toe of the dam. The asphaltic concrete is to join this wall, making the entire upstream slope of the dam water-tight.
The proposed spillway will have a breadth of 250 feet and ample capacity to handle any flood. It will discharge on a broad terrace several hundred feet from the edge of the cliff, and even if the shale does wear somewhat it is believed that the spillway will be permanent over the terrace. It is proposed to pave the spillway with asphal
tic concrete for 300 feet below the crest on account of the folded and fractured condition of the shale.
The outlet from the reservoir is to be through a tower and tunnel near the north end of the dam, as shown in fig. 22. The tower is to be of concrete, is circular in plan, and will contain the valves for controlling the flow from the reservoirs. Five intake pipes 3 feet in diameter will be placed in this tower. The valves will be the ordinary disks
or covers, which will be lifted by a rod and geared wheels. The outlet gates from the tower are to be ordinary slide gates on rollers, with a clear opening of 2 by 4 feet. They will be operated by means of a rod and geared wheels, like the inlet valves. These outlet valves will normally remain open, but may be closed or partly closed in case the inlet valves should fail to close or break. They will also serve to regulate the pressure in the tower in case it is difficult to operate the inlet valves. As the water will be used solely for irrigation, the
valves were placed near the bottom of the tower. If desirable, howerer, others can be placed at different levels at any time. The outlet tunnel is to be driven through shale rock and lined with concrete. As at the Foster site, the location of the spillway and dam is favorable for cheap and rapid handling of rock by means of two overhead cableways. The rock when blasted will doubtless shatter into sizes easily handled, probably into sizes small enough to be loaded into skips with a steam shovel.
The following is a summary of the estimated cost of the dam and reservoir:
Estimated cost of ('urrier dam and reserroir. Loose rock fill in dain
$184,130 Asphaltic concrete
69, 191 Hand-laid rubble
19, 9:36 Cut-off wall
36,016 Wing wall north of spillway Pavement on spillway
6, 415 Outlet tunnel
11, 895 Outlet tower
11,610 Inlet valves
4, 3.30) Outlet valves
3, 900 Tower house and footbridge
500 Engineering and contingencies, 5 per cent
17,809 Reservoir and dam site
The estimated cost of storage at this locality is $1.5.47 per acre-foot if the reservoir is filled once during the winter, or $7.74 per acre-foot if filled twice, as described on page 85.
As the discharge of this stream is always sufficient to fill both the Foster and Currier reservoirs at least twice during the wet season, the outlet gates and tunnels were designed to discharge the contents of the reservoirs in thirty days. This amount of water can easily be handled in the valley below for winter irrigation. The impounded water can be released in the stream channel below the Currier dam and picked up by the existing and proposed canals at the month of the canyon, as shown on Pl. II.
SAN LORENZO CREEK.
The only stream of any importance entering the Salinas from the east, except Estrella Creek, is San Lorenzo Creek. (See Pls. I and II.) This stream leaves the Mount Diablo Range about 15 miles above its junction with the Salinas. Its easterly tributary, Lewis Creek, rises in the most elevated portion of the Mount Diablo Range, in Priest Valley, and flows northwestward in a deep valley in this range to within about 5 miles of its junction with Peachtree Creek, a stream that drains the southwestern slope of the long, narrow ridge between Priest Valley and the low-lying mesa lands to the south west. This