Principles of training Rivers through Tidal Estuaries. 507 



more or less different conditions. The following description is there- 

 fore given of the results of investigations, carried on at intervals 

 during more than two years, with reference to the proposed extensions 

 of the training works in the Seine estuary, which appear to afford a 

 fair assurance that a similar method, applied to any estuary, would 

 indicate the effect of any scheme of training works, provided the 

 special conditions of the estuary were known. 



Investigations about the Seine Estuary. 



The training works in the lower portion of the tidal Seine, com- 

 menced in 1848, had reached Berville in 1870, when the works were 

 stopped, in the interests of the port of Havre, on account of the large 

 unexpected accretions which were taking place behind the training 

 walls, and at the sides of the wide estuary below them.* The original 

 scheme, proposed in 1845 by M. Bouniceau,f comprised the extension 

 of the trained channel to Honfleur on the southern side of the estuary, 

 and the prolongation of one or both of the training walls towards 

 Havre at the north-western extremity of the estuary, as in any 

 scheme, the interests of both these ports, on opposite sides of the 

 estuary, have to be considered. The works are acknowledged to be 

 incomplete ; and great interest has been evinced, particularly within 

 the last few years, in the question of their extension, so that the 

 shifting channel between Berville and the sea may be trained and 

 deepened, and the access to Honfleur improved, without endangering 

 the approaches to Havre. The objects desired are distinctly denned ; 

 but the means for attaining them have formed the subject of such a 

 variety of schemes, that hardly any part of the estuary below Berville 

 has not been traversed by some proposed trained channel, except the 

 portion lying north of a line between Hoc and Tancarville points, 

 which is too far removed from Honfleur to be admissible lor any 

 scheme. Altogether, including distinct modifications, fourteen schemes 

 have been published in France within my knowledge, seven of them 

 having appeared within the last five years. The schemes also exhibit 

 great varieties in their general design J (Plate 2, figs. 1 and 3 ; Plate 3, 

 figs. 1 and 2 ; and Plate 4, fig. 1), illustrating very forcibly the great 

 uncertainty which exists, even in a special case where the conditions 

 have been long studied, as to the principles which should be followed in 

 designing training works. It is evident that no reasoning from analogy 

 could prevail amongst such very conflicting views ; and having had the 

 subject under consideration for a long time, the idea occurred to me in 

 August, 1886, of attempting the solution of this very difficult problem 

 by an experimental method, which might also throw light upon general 



* ' Instit. Civ. Engin. Proc.,' vol. 84, p. 241, and Plates 4 and 5. 



t ' Etude sur la Navigation des Rivieres a Marees,' M. Bomuceau, p. 152, Plate 2. 



I ' lustit. Civ. Engin. Proc.,' vol. 84, p. 2^7, and Plate 4, fig. 9. 



