460 



Tides in Estuaries 



for the spring tide of 19 September, 1876. The high water line rises slowly 

 but continuously from the mouth to the tide mark by somewhat more than 

 2 m, i.e. there is a rise of 2 m over a distance of 150 km, which must probably 



18 



23 22 21 20 19 18 17 16 15 14 13 Noon II 10 9 8 7 6 5 4 3 2 I hr 



30 

 ft 



25 



20 

 15 

 10 

 5 



23 22 21 20 19 18 17 16 15 14 13 Noon II 10 9 8 7 6 5 4 3 2 I hr 



Fig. 194. Tide curves of Father Point and Quebec at the St. Lawrence River from 



6-9 October, 1896. 



be attributed to the slope of the river water (head water). For other French 

 rivers (see Table 76) this slope is not so well developed and, over some dis- 

 tance, its direction is reversed. The variations, however, are very small. 



According to Franzius, the same applies for the Elbe and the Weser, as 

 is shown in Table 77 for tides with an average range. The difference in level 

 between the mouth and tide mark is at high water for the Elbe + 1 -28, for 

 the Weser +1-68 m, so not very large. 



On the contrary, the level of the low water (low-water line) deviates con- 

 siderably from the horizontal and shows everywhere a strong slope down- 

 stream (for the Elbe +4- 14, for the Weser +5 06 m). A difference between 

 spring and neap tide is very obvious, as Table 75 shows for the Gironde- 

 Garonne. The low-water line in the lower section of the tide zone lies deeper 

 at spring tide than at neap tide, and in the upper section it is higher at spring 



