474 Tides in Estuaries 



the possibility of the progress of a wall of water on the water surface. All 

 these circumstances are of the same nature for both phenomena, only the 

 dimensions differ correspondingly. 



Phenomena like that of the bore are not limited to estuaries and rivers. 

 Schumacher and Thorade (1923, p. 48) have shown that bore-like rises 

 of the water level occur at low tide in the Prielen (sea shore-rills) of the shallow 

 seashore waters of the German North coasts (Watten meere) (see Fig. 202). 

 Bores appear also in shallow straits, when different types of tides at the mouths 

 can cause similar phenomena, as for instance the remarkable currents and 

 eddies in the Strait of Messina (see p. 395). 



