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20 foot for the passage of smaller vessels, which was also furnished with a pair of gatespointing to Landward ; this cross-wall had three draw-gates, through which the watercould pass for the purpose of scouring out the b:isin.
This upper reservoir is called the Pent, and here the fresh water river which springsfrom the chalk hills north of Dover empties itself, and makes its way through both sets ofgates through all the three harbours, and lastly through the pier heads into the sea.
Smeaton observed that no arrangement could be more judicious, and that it correspondedwith what had been done so effectually at Cherbourg, where immense sums of money hadbeen expended, which was in a most perfect state before it was destroyed by the English .
When there are hard gales of wind and seas from the south-western quarter, a quantityof beach is brought round the western head, and lodges itself between the heads ; the basinand pent are then filled, partly by taking in the sea water, and partly by fresh water affordedby the river, and there retained until low water.
The draw-gates of the sluices in the cross-wall are then opened with all expedition, andthe body of water contained in the basin or pent, by making its way through the pier-heads, cuts down and removes the bar of the beach, which at the time of spring tides isdone with great effect, and at two tides the mouth is effectually cleared.
When there arc hard gales from the south-western quarter, and at the same time shortor low neap tides, such a quantity of beacli is accumulated, that it is with difficulty anentry can be made into the harbour.
The natural direction of the entry is east-south-east by the true meridian, and by themagnetic meridian, when Smeaton took his observations, it was south-east.
The western head was carried out in the natural direction of the harbours entry, forabout 30 feet in a line at or about south-south-east, when it suddenly turned to south-south-west, in which direction, after being carried 60 or 70 feet, it terminated by a salientangle, pointing to the same quarter. The line of direction of this flank of the pier beingcontinued in an opposite direction, cut within the eastern pier-head about 60 feet, so thatall the winds betwixt south-south-west and cast-south-east occasioned the sea to strikeobliquely, and, acting in the manner of a tunnel, bring the seas, when the wind is south orsouth-south-west, and the beach into the harbour’s mouth; the south-eastern seas are soshort, that they do not much affect it, but by the pier turning so much to the west, itgreatly facilitates the beach, after it has passed round this salient point, to get along itsHank, whose line of direction being overlapped by the eastern head is thereby caught andretained when the wind is more to the west than the south-south-west direction of thisHank.
To lessen as much as possible the quantity of beach from getting round and lodgingbetween the pier-heads, Smeaton recommended that the first mentioned line of head shouldhe prolonged in its direction, south-south-east, until it was advanced sufficiently far to comeinto a south-south-west direction with the extremity of the east head, which would requirean addition of about 90 feet. This additional work would form a sort of triangle, the baseof which would be the south-west flank, whose projection forwards towards the south-east,in a line perpendicular to the base, would be but little above 60 feet further out.
By the elongation of these piers, it was not thought that the beach would be effectuallyprevented from entering the harbour’s mouth, but that it would be lessened in quantity, andmore readily removed.
The outer harbour at present contains 7J acres, the inner basin 6j acres, and the pent1 U acres ; a wet dock of l j acres opens into the western side of the outer harbour, whichagain communicates with a graving-dock.
Tlie entrance between the picr-lieads, now formed of stone and brick, faced with timberpiles, is 110 feet in width, and opens to the south-south-east. The rise of average springtides is from 18 to 19 feet, and of neaps from 12 to 13 feet; but the depth of high waterin the harbour at spring tides is only 17 or 18 feet, in the basin from 16 to 17 feet, andabout 3 feet less during neaps. The harbour therefore is left dry at low water.
Vessels on entering, when the south-westerly gales prevail, find great difficulty, as thereis then a heavy sea at the harbour’s mouth, from the bar of shingle which is thrown up, andwhich renders it inaccessible for several weeks together. In addition to three sluices orculverts connected with the inner basin by means of a pipe, there is in the western pier abrick reservoir, communicating by means of a tunnel 30 feet in width, and 16 high, withthe inner basin and pent. From this reservoir five new sluices, 7 feet in diameter, lead tothe extremity of the pier-head, and from the powerful volume of water thus discharged,and the impetus acquired by the proximity of the reservoir, it has been found sufficient,with the assistance of the sluices in the cross-wall between the basin and the outerharbour, to remove the shingle from the pier-head, and keep the channel clear to a levelbelow the bottom of the harbour; but this shingle again returns or is thrown up withparticular .winds.
The tide flows from the south-west, at the rate of four miles per hour.
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