San Francisco water . ving decided todredge Islais Creek and thus open it up tonavigation, the pipe-line was cut andplugged on the north and south sides of thenew waterway. As the years passed and the district de-veloped, the desirability, particularly forfire purposes, of having the twelve-inch mainagain connected across Islais Creek at ThirdStreet, and in addition across the Channelat Fourth Street, became apparent. It was therefore decided in 1925 to con-nect the main at the above locations, but dueto the difficulty of getting the required ma-terial, the work was not undertaken untilthis ye
San Francisco water . ving decided todredge Islais Creek and thus open it up tonavigation, the pipe-line was cut andplugged on the north and south sides of thenew waterway. As the years passed and the district de-veloped, the desirability, particularly forfire purposes, of having the twelve-inch mainagain connected across Islais Creek at ThirdStreet, and in addition across the Channelat Fourth Street, became apparent. It was therefore decided in 1925 to con-nect the main at the above locations, but dueto the difficulty of getting the required ma-terial, the work was not undertaken untilthis year. The depth of the water in the Channel aswell as in Islais Creek, at the present time,is about twenty feet below mean low water,but future developments on both these water-ways contemplate a depth of thirty feet. Asships, entering or leaving, might drag theiranchors, it was decided that the pipe-lineshould be at least five feet below the mud-line after the contemplated developments July. 1926 SAN FRANCISCO WATER 11. lbmarine pipeline ready to be lowered, the end of theof derrick barges. were completed. This meant that the mainwould have to be placed at a depth of thirty-five feet below mean low water and thereforea trench would have to be excavated acrossthese waterways having a depth of sixteenfeet, and this was accomplished by means ofa clam-shell dredger. The pipe selected for these two submarinejobs was twelve-inch class B, flangedcast-iron pipe; lead-packed flexible joints tobe placed at proper intervals in the line. Allbolts used in connecting the line togetherwere of Tobin bronze and all gaskets wereof sheet lead. The flexible joints were of theball-and-socket type, with a movement often degrees from their center line. Except in minor details, the work of lay-ing the main across the Channel at FourthStreet and across Islais Creek at ThirdStreet was identical. The entire length of thepipe-line which lay horizontal was first as-sembled on pontoons along the
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