TRANSACTIONS OF THE SECTIONS. #07 



Interception of Rainfall from Sewers. Bu Baldwin Latham, G.E., 

 M.Inst. C.E., F.G.S., F.MS., $c. 



The author observed that the admission of large and uncertain volumes of _ rain- 

 fall into sewers at uncertain periods was attended with considerable difficulties in 

 many districts in which purification of the sewage had to be effected. In the 

 majority of towns the rainfall was admitted into the sewers, the excess of rainfall 

 and sewage being discharged by storm- water overflows, to the great detriment of 

 the streams which received the discharge from such overflows. The complete 

 separation of rainfall from sewers had been advocated ; but considerable difficulties 

 arose from such separation in crowded towns, as in times of rainfall the water 

 flowing from the streets to the sewers was found to be quite as impure as the 

 sewage proper. Moreover, the admittance of rainfall into the sewers necessitated 

 an increase of capacity in the sewers— as, for example, London, where two thirds of 

 the total capacity of the sewers was required for carrying away the moderate 

 quantity of a quarter of an inch of rainfall in twenty-four hours. The author had 

 carried out a complete system of sewerage in the Borough of Longton and in the conti- 

 guous district of the East Vale Local Board, the combined districts containing a popu- 

 lation of about 25,000. The sewage was taken under an arrangement with His Grace 

 the Duke of Sutherland, the adjoining landed proprietor, and used for irrigating land. 

 A duplicate system of sewers had been carried out, a connexion being made 

 between the rainfall-sewers and the sewers proper, and what was termed an "inter- 

 ceptor" was provided at the point of junction between the two systems of sewers. 

 The interceptors consisted of a leaping weir so arranged that when there was a 

 small quantity of water flowing down the rainfall-sewers, and the liquid as a 

 natural consequeneo was very polluted, it passed through an adjustable opening 

 into the sewer proper ; but in time of rainfall, when the volume and velocity of the 

 stream in the rainfall-sewers was increased and the water was comparatively pure, it 

 leaped over the opening into the sewer and passed to the natural streams of the 

 district. The cost of such interceptors was about £31 each, twenty-two of them 

 being used in the district of Longton and East Vale, and their employment gave 

 the most perfect satisfaction to the authorities. 



Indications of the Movement of Subterranean Water in the Chalk Formation. 

 By Baldwin Latham, C.E., M.Inst.C.E., F.G.S., F.M.S., #c 



[Plate V.] 



It is a matter of considerable importance to the engineer that he should be able 

 to determine with accuracy the direction of the flow of underground water, as both 

 the volume and quality of the water to be procured at a particular spot in well- 

 sinking depend upon knowing the extent of the contributing area and the direction 

 of the flow of the water. 



A very large number of observations have been made by different persons on the 

 relative height at which the water stands in wells in the Chalk formation. The 

 Rev. James Clutterbuck, Mr. John Evans, F.R.S., Mr-. J. Lucas, F.G.S., the author, 

 and others have shown by direct measurement that the water in the chalk and 

 other geological formations does not stand at what is termed a " water-level ;" and 

 what is known as the " water-level " of subterranean water is usually a line having 

 a considerable declivity. The very fact of water standing at such a declivity is 

 clear evidence of movement ; and the observed declivity is called the angle-friction, 

 or the measurement of the resistance of the water in moving through the strata, 

 just the same as the fall in the surface of an open stream is the measurement of 

 the resistance the water meets with in its passage down the channel of the stream. 

 ' It was pointed out by Professor Prestwich, some years ago, that subterranean 

 water is governed in its movement by the same laws as regulate surface-streams. 

 The more the question of movement of subterranean water is Investigated this is 

 found to be the case. The greatest elevation of the subterranean water is usually 

 found under the highest lands, and the least elevation under the lands having the 

 lowest level. The flow of water laterally is from the hills to the valleys, and 



