190 



Long Waves in Canals and Standing Waves in Closed Basins 



ference of the amplitudes of the tides was the main cause of the Euripus cur- 

 rents. The maximum differences of 1 m in the northern harbour and of 20 cm 

 in the southern harbour changes its sign every 6 h and, consequently, causes 

 these strong currents. The "reversal of the high waters" in Khalkis was 

 previously considered a peculiarity; it describes the fact that the times of 

 the high and low water on the 9th lunar day are just interchanged from 

 those of the 6th lunar day. The same is true for the 23rd in comparison with 

 the 21st lunar day. It is a phenomenon which necessarily results from the 

 tidal constants and which is somewhat strengthened by the fact that the 

 ratio of S 2 : M 2 for Khalkis is 64, which is considerably higher than the 

 normal value of 0-46. 



The narrows of Khalkis can be considered as a wall which almost com- 

 pletely closes the Evoikos and Evrippon Euripus, because, as a consequence 

 of its small cross-section, there can hardly be any exchange of the water- 

 masses through it. Therefore, the tides of both the northern and the southern 

 canal will be a co-oscillation with the tides of the Aegean Sea at the respective 

 openings of the canal. Sterneck has computed these co-oscillating tides for 

 the two canals, taking fully into account their bottom configuration, and he 

 obtained the range of the tide along the longitudinal axis of these canals 

 up to the narrows of Khalkis, as represented in Fig. 81. Despite the nearly 



I i 



Oreos ! Trikeri 

 Con I Con. 



I I 



100 80 



South 



60 40 



20 



20 



km 



40 60 



80 



100 120 140 

 North 



Fig. 81. Range of the semi-diurnal tide in the Euripus Channel co-oscillating with the 

 Aegean Sea in the north and in the south. 



equal amplitude of the semi-diurnal tide at both the north and south opening 

 of the channel in the Aegean Sea, the amplitude of the tide in the northern 

 canal rises first rapidly and then slower to 79 cm in the northern harbor of 

 Khalkis. In the southern harbour, on the contrary, the rise is very small and 

 the amplitude only attains 23 cm. These theoretical values show a very good 

 agreement with the observations of Miaulis. They also explain fully the an- 

 normal value of the ratio S 2 : M 2 for the penetrating tides and the small 

 value of the diurnal tides. They also explain the reversal of the high water 

 hours, which is linked with the reversal of the regular current before and 



