A Treatise On The Principles And Practice Of Harbour Engineering

HARBOUR DESIGN 25 to a bar, a spit or horn (fig. 20), through which the river, in times of flood, may break, but which generally reforms. In either case the shoaling is Fis. 19.—Harbour of Ceara. Effect of breakwater. detrimental, and various means have been tried to remove it. The most generally accepted methods are by means of projecting jetties, or training walls, and dredging. Unless the former are extended into very deep water, they are not likely of themselves to pruve completely efficacious. Accretion takes place as shown in fig. 22, and matters readjust themselves a little further out much to the same effect as before. Fig. 20. The history of Dunkirk, Calais, and other French ports, proves this, the jetties constructed at chose places having to be prolonged from time to time, as shoaling has accrued. The works at the mouth of the Mississippi (where there is, of course, some Fig. 21.—Entranee to Christchurch Harbour. Formation of spit. difference in the tidal conditions)1 are of the same nature, being designed for the removal of a bar; but the jetties are of considerable length, and, being 1 The tidal range in the Gulf of Mexico is very small.