S8 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[March, 



obtain at the junction of their district with yours ;— your answer was, " the 

 greatest depth that can be obtained." In lowering their outlets, the city 

 have accordingly afforded the greatest depth they could ; the Tower Hamlets 

 express their intention to do the same. The covered portion of the Holbom 

 and Finsbury divisions appears to be greater than any other district north of 

 the Thames, the return of houses rated to the sewer rate in 1833, as made to 

 the House of Commons, showing an excess of 723 houses above the "West- 

 minster district. 



In the Holbom and Finsbury divisions there are about 98i miles of covered 

 sewers for house drainage, exclusive of several miles in length built by indi- 

 viduals, previous to the present regulations being made ; there is also about 

 IS* miles of sewage for the surface drainage, and about 10 miles of open 

 sewers. 



In a large proportion of the covered sewers from various causes, accumu- 

 lations of foul deposit obtain. These accumulations existing beneath the 

 streets in a state of ferment for many years, were a cause of much disagree- 

 able and unhealthy effluvia, and were a further annoyance to the public by 

 choking up the private drains when they attained to any considerable quan- 

 tity. The remedy for the evil, when complained of, was only to be had by 

 raising the noisome substance in pails to the level of the street, and carting 

 it away ; a process which, in itself, was subject to many manifest objections, 

 and made the breaking up of the pavement and roads, and the consequent 

 obstruction of public thoroughfares, unavoidable. 



On a general examination into the causes of deposit, one thing that ar- 

 rested attention was this, viz. that in sewers of the same form and with the 

 same fall or inclination, a different degree of accumulation was found to exist. 

 In some instances this difference was occasioned by the common run of 

 water being greater in quantity in one sewer than another. In other sewers 

 the current of water coming in, where old sewers improperly met at right 

 angles, was found to cause, at thejunction of the two streams, an obstruction 

 to the flow along the main line, and here deposit accumulated; and where 

 the collateral sewers were connected with the main line at right angles and 

 at different levels, the obstruction was still greater ; for example, in one in- 

 stance where the collateral sewer was 3 feet above the level of the main line, 

 a deposit was formed of a foot in depth, extending in a shoal up the stream 

 to the length of several hundred feet from the point of junction, while below 

 that point the sewer was perfectly clear. It was also observed, that where a 

 gully neck delivered the surface water of the street or road into the sewer 

 through the crown of the arch, an obstruction was caused in the sewer and 

 deposit accumulated largely on the up-stream side. The whole of these ob- 

 structions tended to lessen the capacity of the main line of sewer. The ine- 

 quality of the bottom of many sewers, and the little fall in others, were 

 causes of accumulation of deposit, and the common run of water in many 

 sewers was found to be insufficient to carry the deposit away. 



To remove accumulations from the sewers in a way less offensive than the 

 prevalent mode, to construct the sewers on such principles as were likely to 

 lessen the cause of the formation of deposit, became subjects of consideration. 

 Levels were taken through the Holbom and Finsbury divisions, to ascertain 

 the practicability and expense of remodelling the sewers and rebuilding them 

 at the lowest level which the outlets would afford ; but it was found that the 

 level was such as would not give that fall to the sewers as would secure the 

 passing off of the foul matter with the common run of water, and that the 

 utmost that could be obtained would be the natural cleansing of one-half of 

 the sewers, while the remaining portion would still require artificial aid. The 

 cost of lowering the sewers to obtain this partial relief would be, as before 

 Stated, nearly a quarter of a million sterling. 



This result the surveyor communicated to Mr. Donaldson, the chairman of 

 the Westminster Commission, who, on examining in July 1840, the flushing 

 apparatus now in use, agreed that it would do well for old sewers, but ex- 

 pressed a desire that all new sewers should have such a fall as not to need 

 flushing. 



There being a current of water of greater or less quantity in all sewers, in 

 some constant, in others periodical, the idea presented itself of turning this 

 ordinary current to advantage in preventing the accumulation of deposit ; 

 and to do so, the use of dams at certain distances asunder, to collect heads of 

 water, was thought of. 



A series of experiments was commenced in order to ascertain what ve- 

 locity could be obtained, and how far such flushes of water would maintain 

 Telocity sufficient for the purpose required. These experiments were made 

 with board dams fixed in the sewers, and the results led to the conviction 

 that the deposit might be removed at less expense by this than by the pre- 

 valent method. In making experiments it was observed that the effect was 

 the greatest when the dam was removed the quickest. Sufficient data having 

 been acquired, the matter was laid before you, and a great number of open- 

 ings were directed by t^e Board to be made in various sewers having different 

 degrees of accumulation, that you might personally see the effect of the plan 

 on an extended scale. / The result proving satisfactory, you encouraged the 

 idea, and several of your body made very valuable suggestions upon the 

 •various methods of appli &tj on which were brought before you ; and a report 



was directed to be made upon the system of Hushing, and on other suggested 

 improvements which you were pleased to adopt. In that report it was stated 

 that the average yearly cost of cleansing was about 900/. per annum. To 

 this there would in future have to be added the cost of cleansing such sewers 

 as had not then been cleansed, but in which deposit was accumulating, and 

 in time would need removal. An example of this class of sewers may be seen 

 in the extensive sewage on the Whiskin estate. Clerkenwell. These sewers 

 have been built about twenty years, and have not required cleansing until 

 this winter. The different degrees of accumulation in these sewers show 

 also many of the causes of accumulation where sewers are well built and 

 have a good fall in them. For instance, the sewer in Meredith Street having 

 a constant flow of water turned through it from St. John Street Road is kept 

 free from deposit, whilst in the sewers in Whiskin Street, Skinner Street, 

 Coburg Street, and the upper part of Gloster Street, the common run of 

 water being too small to keep them clear, deposit accumulates ; and in the 

 lower part of Gloster Street, where the junction with Meredith Street was at 

 right angles, the deposit had accumulated to nearly twice the depth that it 

 had done in the other sewers. Of this class of sewers that would gradually 

 come under the necessity of cleansing, there is about 97.498 feet, which, esti- 

 mated at the quantity of deposit contained in the above named sew ers, would, 

 by the old method of cleansing, involve an expense of 244/. per annum, in 

 addition to the sum before named. 



In the Report before named, it was stated that if the average sum which 

 the cleansing then cost was applied for seven years, and the cleansing done 

 by flushing, the apparatus and side entrances might be fixed to the sewers 

 without any extra charge whatever, and the public would, at the end of that 

 period, derive the benefit of a saving of nearly 800/. per annum, besides se- 

 curing, during those years and for the future, a saving of 300/. •per annum in 

 the item of cleansing, which the Commissioners had effected under their then 

 existing contracts. The flushing system being adopted by you, the method 

 of carrying it out was ordered to be as follows, viz. that when a sewer was 

 complained of and required cleansing, the foul deposit should be flushed 

 away, and apparatus fixed to enable it to be kept free from accumulations of 

 deposit in future. The result to this time is as follows. Since the com- 

 mencement of the system of flushing, the foul deposit has been washed away 

 from about 16 miles in length of old sewers, on which have been placed 59 

 side entrances and 67 flushing gates. After deducting from the cost of 

 removing this deposit by the old method, the expense of all the side en- 

 trances and flushing gates, there remains a saving of 445/. 13s. 6</„ and the 

 side entrances and apparatus are furnished for future use. These sewers are 

 about 2-7ths of those that appear to have deposit accumulate in them ; and 

 2-7ths of the average annual cost of cleansing by the old method would be 

 326/. 17s, The annual cost for men to work these gates is 106/., forming a 

 saving of 220/. per annum on these 2-7ths of the sewers. The total cost of 

 flushing apparatus to these 2-7ths of the length of the sewers has been 434/. 

 thus whenever that apparatus should require renewing, the amount of two 

 years' saving will renew the whole. It is not likely they will require renew- 

 ing for between 30 and 40 years, if then. It is very probable that the 

 interest of the saving will keep the apparatus renewed. There is also the 

 saving to individuals of the cost of cleansing [private drains, which, by the 

 system of flushing, can never become choked by accumulations in the sewers 

 as heretofore ; and when it is considered that many sewers required cleansing 

 every fifth year, the amount of expense and annoyance must have been con- 

 siderable. Another benefit has been the avoidance of breaking up the pave- 

 ment and roads, the cost of replacing which for holes that must have been 

 made to cleanse the sewers that have been flushed, would have been 370/. 

 The raising large quantities of foul deposit to the surface, to the annoyance 

 of the inhabitants and passengers, has been prevented. And the side en- 

 trances and flushing where they occur have afforded facilities for the men to 

 rake the deposit from old gullyholes into the sewers, from whence it is 

 washed away, thus preventing the breaking up the paving round the gully- 

 holes, and a saving in the article of cartage of the deposit. In one year and 

 a half the saving from this cause in the amount paid for reinstating paving 

 round the gullyholes alone has been 101/. 8s. id. A misconception appears 

 to exist that each flushing gate requires a man to look after it ; it may not 

 therefore be irrelevant in this place to state that one man will be able to look 

 after and manage all the flushing gates that may be placed in a district con- 

 taining 15 miles of sewer. 



With respect to private drains, the flushing gates are placed on such a 

 principle that, if the whole of them were shut for twelve months together, 

 the houses draining into the sewers would not be at all affected by the water 

 in the sewers ; but these gates are never shut except periodically to collect a 

 head of water, and after the head is let off the gate is fastened back, so that 

 no obstruction whatever is caused any where by the application of the sys- 

 tem of flushing. At present, as above stated, the flushing gates are placed 

 in such a manner that if kept shut for months together, the water would not 

 enter the private drains ; but the result of experiments made upon this point 

 was such as induces the surveyor to state.it as a matter worthy future con- 

 sideration.! 



