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HISTORY OF ENGINEERING.

Book I.

Sarultcich Haven was a flourishing sca-port at the time the Isle of Thanet was surroundedwith navigable water. Great changes have occurred by the silting up of the channels,which have been caused by the deposit of mud from the sea water, which is suspendedin the water as long as it is agitated ami kept in motion, but immediately it becomes atrest in an arm of the sea, or within shore, it subsides and is deposited.

Wherever the quantity and agitation of the water is too little, or the mud too great to hekept in motion, then its natural tendency is to rest. “ Every creek, inlet, or bay,” saysSmeaton , “that has not a sufficiency of fresh water to keep it open, by being dischargedthrough it, has a tendency to become land. While such a creek or bay remains deep,a quantity of tide water flowing in and out twice a day, tends to keep the mud inagitation and from settling; but as the tide of ebb is naturally weaker than the flood,the ebb will not carry out all that the flood lias brought in ; and when the depositionis so far advanced as to contract the breadth of the water, and render it to a certaindegree shallow, the quantity of water flowing in and out being lessened, its power isweakened."

The natural means whereby an inlet is kept open is the discharge of a freshwater riverthrough it, which opposing the influx of the tide, and adding to the force of its ebb, willalways maintain a certain channel, in proportion to the quantity of land water that requiresto be discharged. The tendency of nature is to contract the channel to such a size thatthe power of the stream can just maintain it, and in this state the wide extended arm ofthe sea, anciently flowing by Sandwich, and up the general valleys, as now called, seemsto have been at the period that the new cut at Stonar was projected and executed.The Stour was never adequate to keep open so large an arm of the sea as that throughwhich it flowed, and the force of its current was impaired by its meandering course. Thedeclivity of its bed in time becoming less, and the drainage of the lands more imperfect,they turned the river through the narrow neck of land at Stonar, where in the space ofg of a mile there was a fall of a fathom.

'The land floods, after heavy rains, are the clearers of the channels of rivers to sea, andthis is chiefly effected when the tide is out, and most of all when they happen at the lowebb of a spring tide ; at such a time more is done in a few hours than in months where thereflow is leisurely and moderate; one tears away all deposit with violence, the other grindsaway but small particles of mud or sand, and a gentle reflow does not disturb a particle;but, on the contrary, if the preceding tide of flood has brought any silt with it, such areflow will allow it to be deposited, and where nothing is done towards its removal in onetide, no number of repetitions will effect it. As long as the top waters are drawn offthrough the flood-gates of Stonar and the dribbling of the floods, and the ordinary current ofthe river left to go quietly round by Sandwich, no improvement can take place in theharbour.

John Smeaton , who made his report in the year 1789, observes fully upon the greatinjury sustained by the harbour, in consequence of the changes made for the sole purposeof draining the land, and improving its condition; he professes himself as great a friend todrainage as to navigation, and observes that the flooding of low grounds in the valleys ofrivers is an advantage, provided it is done at suitable seasons of the year, and that the soiland manure brought down from the high lands and deposited on the surface of the lowlands greatly improve their fertility ; that the lands are not injured by the height or depthof water which remains upon them for a short time, but the contrary: the damage arisesfrom the continuance of a small depth of water, which must be entirely removed from thesoil before its fertilising powers can be called forth.

For the improvement of this harbour, he suggested that during the winter months,instead of drawing the gates when the water was just above the mark, after a dry season,they should remain shut for a few days, that the water might be permitted to overflow themeadows, and run again in its ancient course ; and that as much of the top waters as couldbe made to pass Sandwich Bridge should be directed or allured that way in order that thewhole channel of the Stour should be kept open.

A scouring power, acting by intervals, through Sandwich Harbour, together with theaid of the hedge-hog and spade in some particular places, might keep it clear.

The harbour has, however, grown both narrower and shallower, and the contractionof its section is a natural consequence of the loss of the force of the top waters of the landfloods

Whenever a fresh water river makes its way to the sea through the loose sand and siltthat the sea has deposited, its course is continually varying ; and when curved, the water,acting on the side, tends to increase its departure from a straight line; to alter this by thespade is a useless and endless work, and jetties are inefficient, as they will make freshcurves where there were none before.

Ramsgate Harbour _As early as the reign of Edward VI . an attempt was made to form

an harbour from Sandwich into the Downs, and traces of a canal may be seen between