358 



Tides and Tidal Currents in the Proximity of Land 



An example of this can be found in the western part of the North Sea, off the coast between 

 Forth and Humber. Here high water occurs at the time of the maximum of the current, which 

 runs parallel to the coast, so that the co-tidal lines are perpendicular, the co-range lines parallel 

 to the coast. It shows clearly that where the coast is convex to the sea, s of M 2 tide varies rapidly, 

 whereas this value varies slowly if the coast is concave to the sea. This can be observed particu- 

 larly well at Flamborough Head between Whitby and Brindlington. Further examples can be found 

 at the south-east coast of Ireland (described by Taylor, 1919, p. 32). At Wicklow Head there is 

 a considerable retardation in the progress of the tide wave. In Wicklow, a few miles north of the 

 cape, high water occurs at 10 h 53 m, which is 2 h 30 m later than in Arklow, 1 1 miles south of 

 the cape. There is another example at Greenore Point (south-east corner of Ireland). The time 

 of high water at Saltees, about 10 miles south-west of Carnsore Point, is 6 h 6 m, at Carnsore 

 Point (4 miles south of Greenore Point) at 6 h 25 m, however at Tuskar Rock (4 miles off Greenore 

 Point) at 6 h 10 m, and in Wexford South Bay, on the northern side of the cape, at 6 h 5 m. 

 The disturbance north of the cape in the Wexford Bay is apparently so great that here the co-tidal 

 lines run for a short distance in the opposite direction. 



Fig. 149. Tide wave travelling from the right to the left, diffracting on a small island. 

 , co-tidal lines , co-range lines. 



Proudman has also studied how different coastal configurations influence 

 the tide waves. In this case one deals with diffraction of the waves at these 

 irregularities of the coast, whereby the ocean depth is supposed to be constant 

 (vertical shores). Although in nature these conditions apply only approxi- 

 mately, yet one gets an idea as to how the co-tidal and co-range lines are 

 changed by such orographical coast disturbances. The corresponding mathe- 



