The Elements of economic geology

Bibliographic data

Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part IV. Engineering geology

Collection:: Economics Books

WATER SUPPLY 227 \/ . J conditions similar to that in the pipes. The block of sand- stone would behave as a continuous chain of piezometers. If there were no outlet the water would saturate the block to the level of the water in the tank; the water-table would coincide with the hydrostatic surface. If there be a free outlet the water-table would be the hydraulic gradient from the water-level in the tank to the outlet, and would vary with the porosity of the sandstone. If the sandstone were re- placed by a block composed of layers of sand and clay the water-table would be an irregular surface; the water would rise to different heights according to the permeability of the material; the greatest possible height would be that of the water-level in the tank. If part of the block were heated by a lamp, then the water near it might be raised above the hydrostatic surface by gas-pressure. The resistance to the underground flow of water by friction limits the yield of wells. If a well be over-pumped a conical area around it is drained of water and the well fails until the * cone of exhaustion ” is again filled from the surrounding bed. Wells on the seashore often yield fresh water, as they drain land water flowing to the sea; but if such a well be over-pumped sea-water enters the cone of exhaustion and the well becomes brackish. The cone of exhaustion was used by George Stephenson in the construction of the Kilsby Tunnel near Northampton. It was feared that the tunnel could not be made until the whole of a water-logged bed had been pumped dry. Stephen- son realized that by pumping a continuous series of cones of exhaustion the tunnel could be constructed although a sloping bank of water rose above it on both sides. Tre Yierp oF WELLs—WATER - StoraAGE—The water- level in wells depends on the local hydraulic gradient. The yield of a well depends on the capacity of the adjacent beds or rocks as regards storage, permeability, and imbibition. The water-storage depends on the total amount of pores in a material, and varies with the uniformity of the grains. If a box be filled with shot of uniform size the total inter- space between them is the same whether the shot be large or small. With a mixture of large and small shot, as the small shot occupy the spaces between the larger, the total interspace is reduced. Similarly in rocks: the amount of

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