METROPOLITAN DRAINAGE.
1 Adam Street, Adelphe, 7th November 1853. Sts,—The streams and rivers of a country being the natural drains where- by surplus fluids are conveyed from the highest levels to the sea, they are the most obvious channels for carrying away all refuse capable of floating in water, and apparently useless to man. As population thickens, the streams become unwholesome ; in tidal rivers an accumulation of fceeal matter is constantly going on, and it becomes needful to provide channels for the sewage distinct from the tidal channels. But in doing this, we cannot de- part from the principles established by Nature, and our most economical course is to follow the tracks she has laid down.
Vaporized water thickening into drops becomes rain ; when it falls on high levels, it seeks the lower by the action of gravity, falling into natural chan- nels. If the channel be of rock, the softer substances accumulated by the torrent are pushed before it and fill the inequalities. If the channel be of clay, the water ploughs it out. If alluvial soil, the same thing takes place so long as the channel is surmounted by sufficiently high banks. If the channel be through a broad alluvial plain or wide valley, the course is con- tinually altering, by the tendency of the stream to carry forward matter which impedes its own passage, and causes it to make detours to right and left and form a zigzag instead of a straight line. This process also by di- minishing the speed of the current increases the deposit in the channel, till the river, overtopping its banks, carves out another and another channel, reaching the sea by many mouths, according as space will permit.
This tendency of rivers incessantly to raise their own beds, produces swamps in level uninhabited countries. In populous districts the river is confined by artificial banks, constantly increased in height as the bed rises; and thus danger of inundation is incurred, as in the Po and Mississippi, 12y the occasional bursting of the banks or &vie. The low grounds of Surrey, Kent, and Essex, being below the level of the tide at flow, would be over- flowed were the banks to burst ; and if remaining so would become marshes, unless' their level could be artificially raised, or means could be taken arti- ficially to raise the water to the level of the river-bed. And supposing the overflow or filtration of the river provided against by a sufficiently deep, wide, and impermeable bed, artificial means must be provided to get rid of the rain-water.
It is clear that the channel of the Thames has sufficient inclination from its source to the sea, notwithstanding its numerous bends, to serve as a sufficient surface drain ; and that if it could be prevented from choking and rairing"ibi bed, it would supply sufficient surface drainage for all ground or sewers above the level of its bed ; and if means were provided for pumping up the fluids from the lower grounds, the arrangement would be complete, save in the pollution of the river and the waste of the manure. If, then, it were a practicable thing to sink a cast-iron sewer or pipe of 501-
dent dimensions just below the level of the mid-channel in the river itself, with communicating-pipes from either hand, the river would be saved from pollution, and the manure might be conveyed to the desired location below by a sub-channel following the course of the upper and unpolluted one. But as it would be inconvenient to lay or get access to pipes laid in mid- stream, the next best course would be to sink a sufficiently large cast-iron pipe at high-water-mark on each side of the river, at a sufficient depth to river ver water into them when required, with entrances at intervals for ex- amination. In this mode the lowest general level would be secured. Pro- vision being made to receive the fluids from below the river-bed levels by pumping, and also for air-shafts to ventilate the pipes, the distribution of the sewage could be effected at any distant spot. The advantages of such a system oser brick sewers would be— Non-interference with the streets ; Great facility of laying down and facility of access; Greater rapidity of execution ; Greater smoothness of internal surface ; Security against the burrowing of vermin; Hardness of surface and security against damage ; Facility of duplicating the pipe! at any lime. As nearly every bed of a watercourse is the lowest ground of the locality, this system of drainage might be applied along all the natural channels, and the application of ventilating-shafts for burning the gases rendered very easy. The power of flushing at will by the river-water at any desired spot is very important. In this mode the river would remain as now, the great conduit for drain- age, with the difference that the polluted fluids would be separated from the water of the river, and also from the atmosphere, by an impervious channel.In using the word pipe, it does not follow that an exact imitation of the or- dinary water-pipes is to be used. The iron channel can be built up of parts connected together in any desired form ; and it would lie safely in any foundation either of mud or other substance, without any tendency to crack or break up for want of a firm support. The material for such a metallic channel would cost about 12,0001. per mile run ; but the cost of laying down would be considerably less than that of digging out and forming deep brick sewers through populous districts. The distance from Twickenham to Barking Creek is somewhere about thirty miles, or sixty miles taking both sides of the river. This would re- quire about 110,000 tons of metal ; and supposing the whole work to be accomplished for 20,0001. per mile run—or the cost of a railway—it would be a cheap mode of purifying the air and water of London and its environs, and of giving additional value to some thousands of acres at any desirable point along the course of the pipes.
The cost of the underground railway to connect Paddington with King's Cross is estimated at 130,0001. per mile run. If it be worth while to do this to connect together two railway termini—for an omnibus traffic is very problematic, underground—it would not surely be difficult to find private capitalists to undertake the work of Metropolitan sewerage along a line of- fering no apparent obstacle. Or the surplus City revenue might supply the funds.
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