388

HISTORY OF ENGINEERING.

Rook I.

the whole became silted up. Before this, the harl>our was sufficiently capacious and deepto shelter large vessels at low water; the sea being suffered at every tide to overflow whatare now extensive marshes in the neighbourhood, by which means a vast body of water wascollected, which, draining off, opened and maintained a spacious channel. In all similarsituations, where the land has been walled in and converted to the purposes of agriculture,the tidal waters, from being confined and lessened in quantity, have lost their power ofcleansing, and wherever there is not a sufficient quantity of land or flood waters to supplythe purpose of scouring, the tendency must be to silt up. Besides this, a quantity ofshingle or beach, derived probably from the constant wearing away of the chalk cliffs onthis coast, was thrown up to the westward, which, being driven on the shore, was thencarried by the currents in a direction nearly west-south-west and east-north-east; the windat any point between south and south-west, now causes the sea to strike the shore ob-liquely, and to heap up greater quantities of beach, and drive it along the shore in thedirection of east-north-east to the lx>ttom of the bay or mouth of the harbour.

Thus, by the silting within, and the throwing up the shingle at the mouth, a surface ofseveral hundred acres of land is formed, and the harbour has lost its value. As earlyas the year 1698, a report was drawn up, which states the harbour to be entirely lost, andin no condition to be preserved for any purpose of navigation. In the year 1719 theAdmiralty Board, under whose direction the former report was made, sent down threecompetent gentlemen to make another survey, after which a new harbour was projected,which was partly carried into effect by Captain Perry, who had previously executed manyconsiderable engineering works in Russia .

The mouth of the new harbour was put 2 miles westward of the old one, where thecoast for several miles extends itself in a straight line, its entrance is nearly at right angleswith the coast, and points south-south-east, or rather south-east by south.

In the year 1763, Mr. John Smeaton reported upon its then condition, and found thatthere was no increase of beach in the harbour; and at the foot of the beach, which is lowwater mark at neap tides, there was a fine firm sand, regularly inclined towards low water,which at spring tides was about 257 yards from the foot of the beach ; and from thenceinclined by very regular and gradual soundings, so as to make 20 feet at low water springtides, and about 23 feet at low water neap tides, at the distance of 1 mile right out of theharbour’s mouth ; these soundings gradually increasing further out, where the bay formedexcellent anchorage ground.

The tides here he found to have the greatest rise of any along this coast, for the commonspring rose above low water mark 23 feet, and neap tides about 14 feet, viz. 17 feet abovelow water mark spring tides.

The direction of the tides was nearly along shore, and very gentle in consequence oftheir distance from the main channel tide, which was of great importance to the harbour.

The design of the new harbour was that of an extended canal ; it had two stone piersprojecting into the sea, as far as the foot of the beach, and the distance between them, whichformed the mouth, was 120 feet; but a quantity of beach having collected at the back ofthe west head, it was prolonged by constructions in timber and stone, until it overlaid theeast pier 210 feet.

From the pier head the harbour enlarged to a width of 200 feet, and at the distance of730 yards within the pier is a large stone sluice. Between the pier head and the sluice,the harbour is formed into the arch of a circle of about 45°; so that no part of the mouthcan be seen from the sluice, nor any part of the sluice from the mouth of the harbour.

The sluice was built of Portland stone, and consisted of two openings, one of 40 feet, shutby folding gates pointing to landward, the other had 30 feet clear water-way, shut by 5draw-gates of 6 feet wide each.

By this contrivance the tide received into the canal above the sluice was shut in, andkept the vessels afloat during the whole time of tide, or was let off at low water by meansof the draw-gates, for the purpose of scouring out the harbour. The length of the canalabove the sluice is about £ mile, and at the surface had a mean width of 150 feet, at thebottom 70 feet, which was the level of the sill of the sluice.

The canal, exclusive of the harbour, would contain about 200 sail of vessels, but not asufficiency of water to answer all the purposes of keeping the outer harbour clean ; it wasconstantly receiving deposits of mud from the Rother and its branches, which brought thewaters from upwards of 100,000 acres of land.

When Smeaton examined the harbour, he found that the bottom of the channel, betweenthe pier-heads, was about 6 feet above low water mark at spring tides, and about 3 feetabove the sill of the sluice, and that in the course of a few years, as the scouring force wasinefficient, the whole would be filled up, if some effectual means were not adopted to preventit. He therefore advised that the Winchelsea channel should be widened and others made,the Rother dammed across, and new sluices built upon it, and that the tidal waters shouldbe suffered to pass the great sluice into all these proposed new channels, and whichwere calculated to contain five times as much water as the original canal above the sluice.