104 IMPROVED FISHERY HARBOUR ACCOMMODA TION 



Hence detritus and silt that would be left in the basin, 

 were there no such current, are carried out again into the 

 open sea." 



During a gale of wind the writer particularly observed a 

 strong surging current setting out past a harbour entrance 

 in a bay, with apparently as strong a stream as out of a 

 river harbour. 



" That the quantity of water so brought in cannot be 

 very small may be judged from the fact that, during a gale 

 in the Irish Sea in 1842, there were counted 9*6 waves per 

 minute, so that about 14,000 waves broke on the shore 

 during 24 hours. Although each wave injected but a small 

 portion of its contents into a harbour, it is quite conceivable 

 that water, returning seaward, should prove efficient as a 

 scouring power, or at least in preventing the entrance of silt 

 near the bottom." It has been recommended in some cases 

 that an opening should be left in addition to the entrance, 

 and such an entrance was left at St. Ives in Cornwall by 

 Smeaton at the harbour. This has since been closed, and 

 an accumulation of much sand having taken place, it has 

 been proposed to re-open it. 



EFFICIENCY OF BACK WATER SCOURING. 



On this subject Mr.T. Stevenson observes: " The profession 

 may be said to be divided into two great classes one indeed 

 placing a very high estimate on the efficacy of back water in 

 preserving the depth of our tidal harbours ; the other on the 

 due regulation of the currents. The one preserves, with the 

 utmost jealousy, every sidelake or bay as being the recipients 

 of what they regard as the grand vis viva of navigations ; 

 and the other are willing to convert indentations, as well as 

 even the wider parts of the estuary, into solid land, by the 



