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r I L I I ~ r ~ I , I'll __ i_ .Lv'oJ I DISTRIHUTION SYSTEM 41 destination the water required by Santa Monica. The Arroyo Seco spillway safeguards the line from Eagle Rock to the Hollywood tunnel against pressures greater than provided for in the design, and a spillway at the south portal of the Hollywood tunnel similarly protects the pipe line from that point to its terminus at Santa Monica. Supplcmental protection against possible surges due to valve operation is afforded by pressure-relief valves. Water reaching the Eagle Rock control tower in excess of that being withdrawn from the Santa Monica feeder flows into the Palos V crdes feeder and is conveyed to the cities served thereby, either directly or after temporary storage in the Palos Verdes reservoir. This reservoir varies in water snrface elevation from a maximum of 320 to a minimum of 270, and its backflow is available to areas served by the Palos Verdes feeder south of 108th Street. In order to deliver water to service areas in the increasingly higher terrain north of 108th Street, four pressure zones at progressivcly greater elevations have been established. The necessary pressure for the lower two of these zones is created by automatic pressure-sustain- ing or throttling valves, one battery of such valves being installed at the Los Angeles River valve station near Butte Street, and an- other at the Compton Creek valve station near 108th Street. The upper two pressure zones are established by the elevation of the pipe line where it passes in tunnel through two ranges of hills. One of these areas of elevated terrain lies adjacent to the Ascot reser- voir of the Los Angeles city water system, and the other is just south of Monterey Road in the City of South Pasadena. The Palos Verdes and Santa Monica feeders are provided with manually operated shut-off valves for sectionalizing the line at in- tervals approximating five miles, so that in the event of damage to the pipe line, any sections remaining unaffected may be isolated for continued partial service. Wherever pressures exceeding those pro- vided for in the pipe design could develop due to faulty operation of automatic or manual valves in the line, pressure relief valves have been installed. As a precaution against accidental loss of water stored in Palos Verdes reservoir there has been installed, in ad- dit.ion to the control valves in the reservoir outlet tower, an auto- matic-check valve at a point in the Palos Verdes feeder a short dis- tance north of the reservoir. In the event of outflow at a rate greater than that normal to operating requirements the check valve will close automatically, preventing further flow of water from the reservoir.