. Water Supply and Irrigation Papers of the United States Geological Survey . ,1. VIEW LOOKING UP THE PACOIMA WASH FROM THE SITE OF THESUBSURFACE 11 VltW OF 50-FOOT SECTION OF SUBSURFACE DAM ON THE PACOIMA WASHSHOWING EXCAVATION AND LAGGING. BLICHTER.] COLLECTING GALLERIES AND 8UBCANALS. (b gravity works are impracticable where the groundwater is at grealdepths or where there is an insignificant slope to the water table. The effect of the removal of ground water from thesoil by means ofan infiltration gallery is, of course, the lowering of the water tabic inthe immediate vicinity of the
. Water Supply and Irrigation Papers of the United States Geological Survey . ,1. VIEW LOOKING UP THE PACOIMA WASH FROM THE SITE OF THESUBSURFACE 11 VltW OF 50-FOOT SECTION OF SUBSURFACE DAM ON THE PACOIMA WASHSHOWING EXCAVATION AND LAGGING. BLICHTER.] COLLECTING GALLERIES AND 8UBCANALS. (b gravity works are impracticable where the groundwater is at grealdepths or where there is an insignificant slope to the water table. The effect of the removal of ground water from thesoil by means ofan infiltration gallery is, of course, the lowering of the water tabic inthe immediate vicinity of the excavation. The curved form assumedby the water table is approximately that shown in figs. 8 (p. 2!)) ami-iiI (p. 73), and is similar to the form of the water table in the neighbor- ^4 O oooo©o©60o 0 ]» CATHERING GALLERIES o o(3) Fig. 42.—Plan of infiltration galleries proposed by Willard D. Johnson. hood of a well. If the infiltration gallery is constructed in close prox-imity to the bank of the river, and if the water collected is used fora city water supply, it is important to know under what circumstancespollution may take place by seep
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