The Elements of economic geology

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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

236 ECONOMIC GEOLOGY 3-18 per cent. In the Queensland wells the decrease is from 3 to 3% per cent. per annum. This decrease in yield has been accompanied in some areas by an increase in the cor- rosive quality of the water, and in some cases by a rise of temperature, in one well amounting to 10° F. in two years. Hence in some parts of the basin the proportion of the plutonic water has increased, showing that some of it is still rising into the water-bearing beds. Town SuppLiEs AND SETTLEMENT—Early settlements are usually limited to areas where there is an available supply of water either from a river or lake or from shallow wells in sand or gravel. Clay in thick beds is only available for residence after a water supply is provided by pipes or aque- duct. London, for example, drew its water from the Thames nearby, until the supply became too impure for domestic use. The suburbs were limited to areas of gravel, for wells in London Clay had to go through it into the underlying sands and chalk, and were too deep and costly for single dwellings. Cities depend for their water either on deep wells or on supplies brought from outside either from rivers or lakes. London now draws its main supply from the Thames above the area affected by the tide. In summer the flow of the Thames over the lowest lock at T eddington is often only 200 million gallons a day, and has been as low as 154 million (August, 1887). Hence as London needs an average from the Thames of 230 million gallons a day, it would require sometimes more than the total flow; and the flow in the Thames must not be reduced by ‘withdrawal to less than 100 million gallons a day. Hence if London depended on a supply drawn daily from the Thames it would often be thirsty. Winter floods discharge as much as 7500 million gallons a day. Supplies are then collected in immense storage reservoirs, which are available for use throughout the year. This system has the advantage that the water is improved and purified by storage; noxious germs are de- stroyed, and the water is rendered innocuous. Cities near mountainous country draw supplies from lakes or artificial reservoirs, for the rainfall is usually high and the run-off carries a high proportion into the reservoirs. Glasgow was the pioneer of this system by, in 1859, drawing its supply from Loch Katrine: Manchester obtains its water

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