ESTUARY HARBOURS, ETC. i$9 



It will sometimes be found beneficial to extend the end of the 

 weather pier by which I mean the one on the side of the channel 

 or harbour from which the heaviest seas come slightly beyond 

 that of the lee pier; the object of such overlap being to partially 

 shut out heavy seas from the harbour, to afford some shelter to 

 vessels before coming abreast of the lee pier in entering, and to 

 give them a better " loose " in leaving the port. 



The passage of drift if it should, as is usually the case, 

 proceed from the direction of the heaviest prevailing seas is 

 also aided in this way; and the outgoing current, with its 

 detritus in suspension, is enabled to trend away to leeward, clear of 

 the entrance, while yet deriving some shelter from the weather pier. 



The extent, if any, to which this overlapping ought to be 

 carried can generally be best decided as the works advance, and 

 it is seen how the entrance works (Fig. 22, p. 156). If the 

 overlapping be carried too far, it is apt to create an eddy, and 

 cause a deposit of drift under lee of the weather pier. It is also 

 objectionable in causing vessels, when entering, to encounter 

 more or less of a beam sea. 



Care should be taken not to give a pier such a direction as to 

 admit of its leading waves up to an entrance. Advantage should 

 be taken of any physical conditions tending to mitigate the force 

 and dangerous character of waves at an entrance. Thus, with 

 the view of preventing their breaking, as well as of affording 

 other facilities, an entrance should be placed in the deepest water 

 possible, it being borne in mind that every additional foot of 

 water at an entrance greatly enhances the value of a harbour. 



A strong current across an entrance should, when possible, 

 be avoided, it being remembered, as stated in a former chapter, 

 that the projection of close piers across a coast current will 

 inevitably increase its strength past the pier- heads. 



The width of an entrance should be regulated (a) by the 

 class of shipping frequenting a port ; (6) by the area of the 

 harbour and the capacity of the tidal compartment; (c) by 

 the quantity of upland water to be discharged ; (d) by the strength 

 of the current running past it ; and (e) by the extent, keeping 

 these considerations in view, to which it is possible to shut out 

 heavy seas. 



The narrower the entrance, within reasonable limits, the 

 more will the action of the ebb and flood currents be concen- 

 trated, and the more effective will they be in maintaining an 



