IX. 



THE CHADWELL SPRING AND TEE HERTFORDSHIRE 



BOURNE. 



Bv John HorKixsox, F.L.S., F.G.S., F.R.Met.Soc, Assoc. Inst.C.E. 



Jiead at JFat/ord, loth November, l8dS. .^**' Zoology *\ 



y C (\ ^ :^ PLATE I. '^ JUL 20 iy42 ' 



The Chadwell Spring. X ^ b h aj o^ 



For nearly three centuries has water been conveyed to London 

 from the Chadwell Spring, and up to the autumn of the present 

 year there is no recorded instance of the failure of this spring. 

 About the beginning of last September it was noticed that instead 

 of water flowing out of the basin of the spring, there was a 

 considerable flow into it, the cuiTent in the cut which connects the 

 spring with the New River being reversed. A dam was then 

 erected across the cut, and the water of the River Lea thus being 

 prevented from flowing into the basin of the spring, the level of 

 the water in it sank several feet — nine feet it was reported, but it 

 was scarcely seven feet below the outlet when I visited it, with 

 our President, Mr. Whitaker, on the 24th of September. 



The first question which should be considered is perhaps the 

 reason why the water fell to this extent. 



It is evident that when it was noticed that the current of the 

 water was reversed, the spring, or group of springs, was acting as 

 a "swallow-hole." Springs such as this are natural openings 

 through which the water in our underground reservoir of saturated 

 chalk readily finds its way to the sui-face. The term " reservoir" 

 may perhaps convey a false impression which should be dispelled. 

 Chalk is a substance which will absorb and retain in its interstices 

 a considerable quantity of water — in fact one-third of its bulk — 

 which, except where there are fissures in the chalk, will only 

 gradually ooze through it : the water cannot freely flow until it 

 finds an open channel. And the plane of saturation in the Chalk 

 is not a well-defined surface as is the surface of a sheet of water. 

 In dry weather, when no water is percolating into it, the Chalk is 

 nearly dry at the surface, and gradually — imperceptibly — it 

 becomes damp, until at last it is so wet that if a piece were cut out 

 and brought to the surface we should see the water slowly ooze out 

 of it. But wherever water runs out of the Chalk, as in springs 

 and wells, it brings away some chalk with it, and so forms 

 channels near the opening and makes it more porous further away, 

 enabling it to hold more water than it does in its original state, 

 and that water to flow more freely. 



Water will not flow out of a spring unless there is water at 

 a higher level than the outlet of that spring ; it is the weight of 

 the water above which causes the spring to rise ; and that water 



VOL. X. — PART III. 6 



