File:Water Supply and Irrigation Papers of the United States Geological Survey (1902) (14586444498).jpg

Identifier: watersupplyirrig6571unit (find matches)
Title: Water Supply and Irrigation Papers of the United States Geological Survey
Year: 1902 (1900s)
Authors: United States Geological Survey
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Contributing Library: Clemson University Libraries
Digitizing Sponsor: LYRASIS Members and Sloan Foundation

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depth to the impervious stratum, and then filling the trench withimpervious material. If the underflow is confined within an imper-vious trough or canyon, it is obvious that such a construction mustresult in bringing it to the surface. An example of this is foundon Pacoima Creek, Los Angeles County, Cal., where a subsurfacedam was constructed in 1887-1890. It is claimed that by means ofthis dam the owners have been enabled to use the bed-rock flow ofwater for the three dry years, 1898-1900, and thereby to successfullycarry through the orange, lemon, and olive growing in FernandoValley. This dam is described in the Eighteenth Annual Report ofthe United States Geological Survey, Part IV, pages 693 to 095; alsoin Reservoirs for Irrigation, Water Power, etc., by James D. Schiller,1901, page 205. A view of the wash up the canyon from the site of the dam is shownin PI. V, A. An underflow was known to exist, as the stream had agood perennial flow back in the hills, shown in the background of
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slighter) SUBSURFACE DAMS. 77 PL V, A, which was observed to gradually sink into the deep gravelwash before reaching the plains. At the site of the dam the canyoDwalls are about GOO feet apart, and the rock floor is at irregular depths,generally from 25 to 50 feet below the surface of the gravel. In constructing the dam, a trench was excavated in successive sec-tions at right angles to the course of the wash. Each section was 50feet long and 5 feet wide, as shown in PI. V, B. The excavation?xtended to bed rock and was boarded up with 2-inch by 8-inch byS-foot timbers and lagged with 3-inch by 4-inch by 5-foot timbers, asshown in PI. V, B, and PI. YI. When bed rock was reached, a smalltrench about 12 inches deep and 10 inches wide was excavated in it,and the construction of the cement and gravel dam was begun. Thewall is about 2 feet thick, and was built up to the surface in the usualmanner, loose surface material being replaced around the dam asbuilt, completely inclosing and supporti

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