Tides in Estuaries 



469 



tides estuaries and have also obtained good results; Hansen's method is a 

 purely numerical one and is a special case of the common two-dimensional case 

 given on page 362. It goes without saying that these methods are of great 

 practical importance. 



3. Bores 



In a large number of rivers the wave profile of the tide wave travelling 

 up the river changes into what is called a "bore" (in French: mascaret). 

 A wall of water with a steep front over the entire width of the river gushes 

 upstream. This phenomenon is characteristic of most funnel-shaped estuaries 

 with shallow depths at low water. In the larger German rivers there is no 

 bore; it is said that there was one in the Ems before its regulation. It is 



Fig. 198. Bore on the Chien-tang-kiang. 



generally found in the French river estuaries and it is particularly well de- 

 veloped in the Seine, where Partiot (1861, p. 71) has made the most thorough 

 study of it, farther in the Orne near Caen, in the Couesnon (designated as 

 Barre, Bay of St. Malo), in the Vilaine and Charente, in the Gironde, but 

 not in the Loire and in the Adour. Of the English rivers which have a bore 

 we will mention the Severn, which was described by Airy and, subsequently 

 by Cornish (1900, p. 44); (1934, p. 101). Furthermore, for the bore of the 

 Trent, Champion and Corkan. (1936, p. 158) have published an exhaustive 

 survey; the bore occurs regularly when the River Trent flows into the Humber, 

 past Torksey and appears in the peculiar form of numerous short waves 

 up to 2 m high, it is called here the eager. In U.S.A. the bore is known to 

 exist in the Petitcodiac River at the northern end of the Bay of Fundy, and 

 Bell Dawson (1899, p. 22) has given an excellent description of it; further, 

 on the mouth of the Colorado River into the Gulf of California. In South 



