TRANSACTIONS OF SECTION G. 641 



This table has been prepared from information derived from careful observa- 

 tion, and the actual run off has been determined by numerous gaugings within 

 the defined areas. The table shows the relation between population and imper- 

 meable surface under the varying conditions which obtain in Manchester, and 

 from it a useful diagram, which will be shown on the screen, has been con- 

 structed. This information was necessary in ascertaining the storm-water dis- 

 charge and time of concentration, which is in direct proportion to the area of 

 impervious surface ; the gradients, of course, also affect the result. 



The formula used in determining the flow of intended sewers has a very 

 important bearing on the results obtained. 



A diagram was displayed showing the discharge in cubic feet per minute in 

 .sewers, computed by various formulae and by actual measurement into tanks of 

 large capacity. The conditions in Manchester afford special facilities for actual 

 measurement which do not obtain in other places. The diagram shows the 

 curve derived from actual measurements and those constructed from calculation 

 by formulfe in general use. It was found that the formula of Kutter coincides 

 with the actual measurements when the value of n (the co-efficient of roughness) 

 is taken as '012 for good earthenware pipes and "015 for brickwork of average 

 construction and in good condition. 



For the purpose of determining the correct sizes of the new culverts, and to 

 prevent the possibility of their proving too small for the requirements of the 

 future, the whole of the areas served by the existing sewers were segregated, 

 and each area was then considered and dealt with separately. The dry-weather 

 flows and the quantities of storm-water resulting from rainfall of varying 

 intensity were measured, and the actual quantities correctly ascertained. These 

 observations extended over a lengthy period. A large mass of valuable in- 

 formation was thus, by many years of careful and systematic record, obtained. 

 If it had been available when the original sewers were designed they would 

 doubtless have been constructed on larger lines ; and, although the initial cost 

 would have been proportionately more, the extra outlay would have been small 

 compared with that now involved. The total capacity of the old and new 

 outfalls below the point at which the excess storm-waters are eliminated exceeds 

 60,000 cubic feet per minute. 



Under the statutory regulations of the Manchester Corporation, the dry- 

 weather flow, which is based upon the water supply, has to be diluted by the 

 addition of six times its volume of storm-water before overflow into the Ship 

 Canal and rivers is permissible. On this basis the main drainage works referred 

 to in this paper will be sufficient for a population of about two and a half 

 millions. 



When the British Association last visited this city (1887) the conservancy 

 system was in use here ; the dry system has subsequently been replaced by the 

 water-carriage system. Since the writer entered upon his duties in Manchester 

 no less than 82,874 cases have been dealt with, and in each case water-carriage 

 was substituted for the dry system, leaving only 1,533 cases yet to be converted 

 from the dry to the water-carriage system. 



The author's new scheme of main drainage was commenced in April 1912, 

 and about nineteen miles of large conduits have been completed since that date. 

 They range in diameter from 15 feet 3 inches downwards. A view of the 

 general arrangement of the main drainage of the city and the outside districts 

 contributing to the scheme will be placed upon the screen. The whole of the 

 drainage is conveyed by gravitation to the disposal works, which are situated 

 about five miles outside the city on its westerly side. The total area at present 

 contributing to the main drainage, including that arranged to be connected to 

 the system, is 39,144 acres : the largest drainage area outside the Metropolis. 

 When the new works are completed the outfalls from the city boundary to 

 the disposal works will be in duplicate. This arrangement has many advantages 

 over one outfall of larger size. In fact, it would not be practicable to con- 

 struct one conduit to convey the quantity for which provision has to be made, 

 especially in those lengths above the principal storm overflow, which i.s situated 

 about half-way between the city and the disposal works. The approximate 

 cost of the new work up to this date exceeds £600,000. 



A portion of the work was carried out by the Corporation staff without the 

 intervention of a contractor. The work so undertaken comprised conduits of 

 1915. T T 



