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<br /> <br />,~ r..." ~ <br />lJ.l't <br /> <br />CHAPTER 8 <br /> <br />Main A11lledllct Tnnnels <br /> <br />THE MAIN AQUEDUCT tunnels are of horseshoe section and are <br />lined with concrete of a minimum thickness of 6 inches on <br />the sides and 9 inches in the arch. All are 16 feet high and <br />16 feet wide, inside of lining, with the exception of Bernasconi and <br />Valverde, where these dimensions are IG feet 3 inches. Their de- <br />signed carrying capacity is 1,605 cubic feet per second. Except for <br />the Colorado River tunnel, which slopes upward from Intake surge <br />chamber to its outlet in Gene reservoir, the Copper Basin No.1, <br />which rises similarly from the Gene surge chamber, and Copper <br />Basin No.2, which will be under slight pressure with full level <br />in Copper Basin reservoir, all main aqueduct tunnels are designed <br />to operate as grade tunnels at all times. <br />The aqueduct route was so located as to reduce the length and <br />hazard of tunnel work to a minimum. Proceeding westerly from <br />the intake to Shaver's Summit, a distance of 134 miles, the <br />terrain rises in roughly parallel north-south steps, marked by <br />the mountain ranges which lie across the route. Beyond this sum- <br />mit a plateau-like area with ridges projecting from its north sur- <br />face extends to Thermal Canyon at mile 150. There the mountain <br />masses change to a northwesterly direction and their rugged south <br />slopes fall away precipitously into Coach ell a Valley with few open <br />areas until Fan Hill is reached. Thence approaching the upper end <br />of the valley and San Gorgonio Pass the fan surfaces are at higher <br />elevations and canyons become numerous with crossings possible at <br />aqueduct grade, but with ridges jutting far out into the detrital <br />fans. For nearly 40 miles through this portion of the Little San <br />Bernardino Mountains between Thermal and Big Morongo can- <br />yons almost continuous tunnels were necessary. <br />On the south side of San Gorgonio Pass the barrier formed <br />by the Coast Range is pierced by the aqueduct line in tunnel <br />through the north flank of the San ,Jacinto Mountains. Emerging <br />from these mountains onto a relatively high shelf forming the <br />southeastern portion of the coastal basin, two low ridges lie across <br />[146 ] <br /> <br />;1 <br /> <br />. J <br /> <br />. . <br />