82 NATURAL SCIENCE. a,^„, 



London itself is provided with water only for present needs, and 

 it is necessary to be prepared for the further growth of its vast 

 population. It is well-known that the amounts of water that can be 

 drawn from the Thames and Lea, and from various wells, have 

 nearly reached their maximum. The average daily amount taken 

 from the Thames above Teddington Weir is about loo million 

 gallons; the minimum daily discharge of water over the Weir is 

 sometimes no more than 153 millions of gallons, although the 

 maximum discharge may exceed 3,000 million gallons, even in the 

 month of August, and is sometimes more than double this amount. 

 The daily maximum amount of water taken from the Thames 

 by the several water companies should not exceed 130 million 

 gallons ; for if more were abstracted, the navigation might be 

 impeded, while the sewage in the lower Thames would not, in dry 

 seasons, be adequately carried away. The Lea is even more seriously 

 drawn upon than the Thames. 



The Chalk under London can no longer be looked upon as a 

 source of great additional supplies of water. This is already utilised 

 by upwards of 200 wells, and while at the commencement of the 

 century the water, when tapped, rose in many places to the surface, 

 it stands now at a level of about forty feet below Trinity high-water 

 mark. It is considered that the rate of depression now varies from 

 one to two feet per annum. 



The effect of the continuous pumping of water from the Chalk 

 has thus been to lower the plane of saturation, whereby the flow of 

 distant springs and streams has been more or less seriously affected. 

 Practically, the amount of water pumped from the Chalk under 

 London is so much taken from the streams that are fed by the 

 natural overflow from that formation. 



Various schemes have been propounded- to supplant and 

 supplement the present sources of water supply for London. It has 

 been suggested that a number of reservoirs be constructed in the 

 upper Thames Valley to retain much of the surplus water in flood 

 seasons, so that it might be sent down, as occasion required, during 

 periods of drought. There has also been a proposal to obtain water 

 at a distance, by means of lakes or reservoirs among the Cumberland 

 or Welsh mountains, or on Dartmoor. 



There is no question but that the present supplies of water for 

 London must be maintained, for their quality is good, and no distant 

 sources could be considered satisfactory in times of disturbance. 

 Additional water will, however, ere long be urgently needed, and it 

 is very important to consider the remote sources that might be 

 available, as Birmingham and other large towns and cities are selecting 

 sites for supplies from our mountain regions. 



Birmingham has been provided with water from wells in the 

 New Red Sandstone, and from surface-water stored in reservoirs. 

 It is now proposed to construct five reservoirs along the rivers Elan 



