344

HISTORY OF ENGINEERING.

Book I.

water, full 14 feet; but at ordinary spring tides there was the same depth upon the bar athigh water, and at low water it was left with only the run of the river over it. The neaptides usually made 10 feet water upon the bar. Outside this bar the water graduallydeepened, and ships rode conveniently at low water, protected from all winds, except thenorth-easterly and easterly, which blew into the harbour’s mouth.

The bar, according to Smeaton , was thus formed; the whole coast, which stretches awaynortherly, is for miles a flat and sandy shore, and the north-east wind acting obliquely uponit brings the sand and gravel intermixed coastwise towards the south; and as the coast,from the south side of the entry, stretches away nearly east for $ mile, these sands wouldbe deposited in the angle of the coast formed at the harbour’s mouth, if the waters of theDee did not force its way through them, which they do, and maintain more or less an openchannel; a hard gale of wind at north-east, bringing the sand and gravel coastwise south-ward, puts also in agitation that which has been previously lodged on the bank on thenorth side of the mouth of the harbour, and at the same time forces it into the entry, andif at that time it happens to be spring tides, and little fresh water in the river, a strong

Fig. 341.

PLAN OP BEARING AND SHEETING PILES,

tide of flood is the consequence; this, together with the wind, carries the gravel and sandinto the channel of the river, and the fresh water being short at the time, the reflux willbe languid, and, impeded by the impetus of the sea, and it cannot return.

I \ 1 I —1—1—L

Fig. 342.

SECTION OF PIEK.

A continuance of land floods, either at spring or neaps, when the wind is moderate fromthe north-east, scours the sand and gravei away from the mouth of the harbour, and carries

11ITO

PLAN OF THE PLATFORM.

it into the roadway, from whence it gets round the point of Girdleness; and if there is witha strong land fresh low spring ebbs, which give the current the greatest fall to sea. and atthe same time run bare over the bar, with a moderate wind to the north-east, the stony