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reservoir, by means of which the amount of water stored for any height can be ascertained. The area of the watershed tributary to this reservoir is 235 square miles. The table on page 71 shows the estimated monthly discharge from tbis stream at the dam site, and the table on page 43 shows the rainfall in the upper portion of the
18 Acre-feet in thousands. FIG. 3.-Capacity curve of proposed Mathews reservoir, showing capacity in thousands of
acre-feet with the water surface at various levels.
drainage basin in Priest Valley. The reservoir is a portion of the canyon of San Lorenzo Creek, where it has cut down through the soft sedimentary formation of the mesa into the granite below. Pl. XI, A, shows the character of this canyon at the dam site. At the dam site the canyon has a width of 120 feet at the level of the stream and 590 feet at the top of the dam.
PROPOSED MATHEWS DAM.
The dam at this point as designed is to be an earth fill. The positions of the dam and spillway are shown in fig. 26. The dam will have a maximum height of 110 feet above the bed of the stream on
the axis of the dam, as shown in fig. 27. The upstream slope is to be 24 horizontal to 1 vertical, and the downstream slope is to be 2 horizontal to 1 vertical. The top width will be 20 feet and the extreme length about 590 feet. The crest of the dam is to be 10 feet above the
level of the spillway. The dam will be made water-tight by a layer of natural bituminous sandstone embedded in the dam, as shown in fig. 27. This bituminous rock can be obtained at the Mylar mine, 6} miles upstream. It is of excellent quality and can be had in large
quantities. A cut-off wall of concrete is to be carried down to bed rock at the upstream toe of the bituminous layer. The depth to bed rock was estimated at 20 feet, but no test borings have been made here. The upstream slope of the dam will be protected from wave action by a 2-foot thick pavement of bowlders and coarse gravel.
The spillway will be excavated through a low saddle northeast of the dam site, as shown in fig. 26. It is to be 200 feet wide and 10 feet deep, lined with concrete for a short distance below the crest, if necessary. This spillway will discharge into a lateral canyon which reaches the main stream 500 feet below the dam site.
The outlet from the reservoir is to be through a tunnel in the granite bed rock and two 36-inch cast-iron pipes, as shown in fig. 28. The flow from the reservoir will be controlled by ordinary straight waygates or valves in this pipe, as shown in figs. 29 and 30. The flow will ordinarily be controlled by the lower gate; the other will be normally open, but can be closed in case of accident to the lower gates, or for repairs. The shaft is to give easy access to the gates. As the water will be used solely for irrigation, the outlet pipe was placed near the bottom of the reservoir, and no provision has been made for drawing off water at different levels.
Earth for the coustruction of a dam lies above the granite bed rock to the west of the dam. It can be delivered at the dam site either by a tramway or by overhead cableways.
FIG. 28.-Profile of outlet tunnel and shaft of Mathews reservoir,
The following is a summary of the estimated cost of the dam and reservoir :
Chalone Creek, which enters Salinas River near Metz (Pl. I), is a torrential stream flowing from the southeastern slopes of the Gabilan Range and Chalone Peak, draining an area of 128 square miles. It also has cut a deep canyon across the mesa lands. The discharge of this stream is large at times, as shown by the character of the channel. There are no reservoir sites in this watershed, and it is of small importance for irrigation purposes.
All the streams along the east side of Salinas River which rise in the mesa region, being without mountain drainage areas, are dry gulches during the dry season and flow but a few hours after storms. in the wet season.
CARMEL RIVER. Carmel River, although not a tributary of the Salinas, is one of the important streams of the region and merits a short description. It rises in a very rough mountain country on the northeastern slopes of the Santa Lucia Range and on the northwestern slopes of the Sierra de Salinas and flows northwestward, reaching Carmel Bay at the northwest extremity of the Santa Lucia Range (Pl. I). The valley is wide between the bounding hills and mountains for 10 miles from the coast, above which the stream flows in a canyon similar to that on the middle section of Arroyo Seco. Above Tularcitos Creek the stream flows in a canyon that reaches far back into the mountain region. Nothing very definite is known about the altitudes in this drainage area, but the average must be between 3,000 and 3,500 feet. The divide between Carmel River and Arroyo Seco is at an altitude of 2,500 feet where it is crossed by the trail. This portion of the Santa Lucia Range is covered with a very thick growth of brush and some areas are well forested by pines.
The Pacific Improvement Company diverts water from this stream by pipe system to reservoirs near Pacific Grove. The diversion dam is 15 miles from the mouth of the stream, at an elevation of 428 feet above sea level. The water is used for domestic supply at Pacific Grove and Monterey, and also for a small amount of irrigation.
The total area of the drainage basin of Carmel River is 275 square miles.
CROPS IRRIGATED. Only a comparatively small portion of the fertile lands of the Salinas Valley is now irrigated. The residents of this region have apparently not until lately realized the need of irrigation, but have placed entire dependence on the rainfall, while vast floods annually