SEW

416

SEW

the sewage matter, and convey it by the shortest route to thenearest river, into which it was to discharge ; this done,their object was attained ; the matter was left to removeitself, or deposit on the banks or bed of the river, as bestit might. This method is now generally allowed to havebeen based upon false principles ; but it must at the sametime be confessed, that to a certain degree it did follow outthe course suggested by nature. That the drainage shouldbe carried towards the river, is not to be objected to ; for itamounts to nothing more than conveying it to the lowestlevel of the district; it is the very course which natureadopts, for rivers and streams are indeed the drains laid outby nature ; the only mistake consists in polluting thesewaters with matters which are prejudicial to health ; had weonly to deal with surface-drains, the system would be rationalenough. Some persons, because this method has been abused,have thought it right to discard it altogether ; we cannotfollow them thus far ; if the area to be drained presentsthroughout one general slope towards the river, we areinclined to think that this would be the most suitable methodof drainage, having the outlet or outlets at the lowest level.If the sewage is to be supplied in its liquid state to tbesurrounding country, it may be advisable to intercept a por-tion ere it reaches this point, but this the circumstances ofeach case must decide ; by such means we should of coursebe better able to irrigate the higher lands, and should alsoeffect a saving in the size of our sewers, for the lower brancheswill not have so large a quantity to discharge.

If again the levels of the main be greatly diversified, orespecially if it consist of basins surrounded by higher ground,it would appear advisable, under any of the above conditions,to provide a separate drainage for each level, so as to avoidthe great depth of excavation which would be necessitated,were the drainage of the higher levels to be connected with amain which had already received that of a lower level. Thebetter plan would be to convey this line through the lowerlevels to its outlet, and to form a separate system for thehigher grounds. Whether it would be advisable to drain allthe low levels together by one trunk-line, and all the highlevels by another, or to drain each level separately, must bedetermined by the circumstances of each special case ; as wesaid before, no fixed rules can be laid down, we can only pro-pose useful hints to be applied as the nature of each casesuggests.

Having disposed of these general matters, we now come toconsider the subject more in detail; but before doing so, letus clearly understand, and determine what we have to do,and what class of subjects we have to deal with. Our gene-ral object is to convey to a distance the refuse, or a certainportion of the refuse, of the town, or other area to be drained,and what does this consist of; it is mainly of two descrip-tions, viz., that which may be particularized as house-drain-age, consisting of the excrements of the inhabitants, and allrefuse matters connected with household economy; and thatwhich is distinguished as surface-drainage, which has espe-cial reference to rainfall and storm-waters. Formerly it wasthe custom to make no distinction between these two descrip-tions ; but of late, we have begun to consider them as sepa-rate items, and a grand question has been raised as to whetherit is correct to provide for them both by the same system ofdrains. In the one case, the supply is, or might be, madetolerably uniform ; in the other, it is periodical and uncertain,nor can it be made otherwise ; it therefore becomes a ques-tion, whether the two can be advantageously combined, butas the inquiry is so mixed up with the determination of thesize and shape of sewers, it will be better to consider it underthat head. We have made no allusion to subsoil drainage,

for it is indeed very rarely required ; if the siirfaee^.^ge,perly drained, there will be no necessity for subsoil c ° n 'except in cases where springs exist, or where the s ff [,etl ie jtain water, and, even in such cases, it is questionab carr it;"the water might not be usefully employed, rather th. r t otaway at a considerable expense. We shall leave t ^ ^ nC e tothe subject therefore out of the question, and turn *the consideration of the sizes and forms of sewei 3.

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Until the last few years, it was the custom ^sewers of a very large size, varying in sectional5 to 100 feet, the former being allotted to coll"ter a ^ e m 9 '' 1in courts, alleys, and side-streets, and the latter to jin*5®outlets into the Thames, the average area lor n ‘being about 12 feet. Now, tbe fact is, that these se^ gtl . e a'"seldom, if ever, fully charged,Ihe sectional area ot ^ ^usually flowing through them, averaging not more oft" 11part of the area of the sewer, and the flow " thescarcely perceptible. In continuous wet weathe , #9

of sewage was greatly increased ; and also on sU fo""fresh water was supplied to the houses; in neither ae n&’ever, was the sectional area equal to £ that "eanl^Jand the only occasion on which the seweis vie ^, 8 uc>

like full, was the occurrence of some very heavy ^ ^ t;V el ve ”perhaps as does not appear once in the course pro"?month. Now, it appeared to those who have recen c j) sn’ a ^fjforward this subject for investigation, that a j e cid ea ,,size would answer the purpose much better, and ;,jipi' eS ^much more economical in construction. Under jjetroP 0 ^* 8 "sion, several experiments were made under ^ ie u ft apP elllVSewage Commission, to test the fact, and the i

to have been decidedly favourable to the new t ,e J . &dg e_• i: _ • tt _noni-se-s 11 ee ’ rruiS 3

In a main line of sewer in Upper Georg® ^ware-road, which communicates directly w’ } nScholars’ pond sewer, and which is 5 leet G ( ^ jnch®^

the larger sewer, and a head-wallsewer, for the purpose of preventing

depth of several inches, so that the stream ^

clnarricVi nn A bp.insr damme j

the

comparatively sluggish, and being damme'* water

‘ ' i the flow ^ieh

the pipe" XT*"* i " fluence onforms the heii If !” vert of the original sewer,

hitirig, an( j „ 0 , t ie pipe, deposit was constantly ^ ^

The superffeinl on . T Partially kept under by repeated jjythree, C^nd 11°™? ° f the ™ter in the pipec,t 7 which ohto-fi f Umes Skater than thesopeiB c ‘. tflCoriginal sewer ln< f , un der the same circumstances, ,° sewer, and the velocity of the whole mass ot

Jvi»S‘in l> e '£ 1 ’

vert o’t

tte r

by 3 feet 6 inches wide, an earthenware P'P e j D ,-

diameter was inserted, laid immediately upon it in 11

built up 111,0 #

any sewa B f t hi3

passing out by a different channel. The tota ve

pipe measured 560 feet, and the whole area r ‘ te & to 119it amounted to about 44 acres. The results are ‘- n the P’fbeen as follows :—“ The velocity of the stie" t ]je vcl oC 'has been observed to be 4^ times greater t 0 ld se "j jU t

of the same amount of water on the bed o jgposib ,jy

The pipe has not been found to contain <l‘ st '!'f e( l,

during heavy rains the stones have been 1 -nearly t0

rattling through the pipe. When the P’P e ^ e gu ffici e11 t \ t ethe velocity and concentration of the water • into ^

clear away any matter which may have ^ een atte r, it ’'v pip"pipe from the large sewers, much of which g ,, 8 tem 01 K 0 fpresumed, would never enter a well-regula e ^ t [ie et>

sewers ; also the force of the water issuing ^ of . jjs-

the pipe, is sufficiently great to keep the ° n j tin" gsewer perfectly clean for 12 feet in length , in" n d

tance, a few bricks and stones are deposi. e ’ ase s. fliein quantity as the distance from the pip® in os ;ts, occ u ’ a" 1 *a certain distance, mud, sand, and other ^P ( | iere ; s ""

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