8o IMPROVED FISHERY HARBOUR ACCOMMODATION 



at pier-heads ; these the writer proposes to term centres of 

 disturbance. 



The accompanying diagram sketch (Fig. 2) represents a 

 compound harbour in an exposed position, although pos- 

 sessed of some amount of protection from certain points. 

 It consists of an inside harbour, an outer or stilling basin, 

 and a kanted pier or breakwater, extending beyond as the 

 most seaward portion of the work. 



There are here three centres of disturbance, the first at 

 the kanted breakwater head, the second between the piers 

 of the outer or stilling basin, the third at the entrance of 

 the inner harbour. 



For the sake of example we will suppose the harbour to 

 look towards the north, and E the point of maximum 

 exposure. The harbour is situated in a bay, the shore 

 rocky, but running first west, then north, and latterly 

 east ; the bottom sand at the position of the harbour, a 

 stratum of clay beneath, overlying rock. 



From the point of maximum exposure, the drift 200 

 miles, from the northward across the bay length of drift 

 five miles, in the direction of the kanted head of the break- 

 water greatest drift four miles, in a westerly direction 

 greatest drift three miles. To use the words of Mr. T. 

 Stevenson, a wave from the point of maxirnutn exposure 

 from the east strikes the breakwater at A, and a portion 

 is reflected seawards ; the portion not so reflected passes 

 onwards, and a part spreads behind the breakwater, which 

 has a free end, running along the inner side, and much 

 diminished in height as it approaches the end of the 

 kanted pier, near the entrance of the stilling or outer basin. 

 A portion of the force of the wave from the pier-head, 

 radiating in its progress, accompanies the first-named wave 

 and joins it in diminishing strength atB, between the piers 



