Principles of training Rivers through Tidal Estuaries. 521 



part their direction, as well as tlie limits of accretion. These are the 

 forces which can be reproduced in miniature in a model, as proved by 

 the close concordance in the channels obtained by experiment with 

 the actual conditions of the Mersey, and with a previous state of the 

 Seine estuary ; and this similarity of results would not have occurred 

 if the other influences noticed above were at all equally potent. 



Training walls mainly modify the direction and action of the tidal 

 ebb and flow and fresh-water discharge ; and, therefore, it is reasonable 

 to suppose that the results in a model, due to these alterations, would 

 correspond to their actual effects in an estuary, provided the important 

 element of accretion could be also reproduced. This was satisfac- 

 torily accomplished in the second stage of the investigation, proving 

 that the miniature influences produced in the model corresponded, in 

 this case also, with the forces acting in the estuary. Accretion is 

 promoted by training walls in an estuary where matter is carried in 

 suspension ; but the action of waves in modifying the channels is 

 stopped by the intervention of training walls. Accordingly, the 

 further the training walls are extended, and the more an estuary is 

 protected by works such as those indicated in Plate 2, the more is 

 the modifying influence of waves eliminated, and therefore the more 

 are experiments in a model likely to correspond with the conditions of 

 estuaries under similar conditions. 



Other considerations also afford grounds for supposing that the 

 effects observed with training walls in a model fairly correspond with 

 the results which such works would produce in an estuary. The 

 charts of the experiments show that definite results followed from 

 certain lines inserted in the model, and that modifications in these 

 lines were followed by modifications in the results. (Compare Plate 2, 

 figs. 1, 2, and 3, and Plate 3, fig. 2, with Plate 4, fig. 1.) Moreover, 

 the results produced with the model agree very closely with the 

 results which, in the two earliest schemes experimented upon, it was 

 stated, before the experiments were begun, would follow, if the works 

 indicated by lines in the charts were actually carried out in the Seine 

 estuary.* 



* Compare the observations relating to Scheme A and Plate 2, fig. 1, with the 

 following extract from * Instit. Civ. Engin. Proc.,' vol. 84, p. 356 : " The narrowing 

 of the mouth of the estuary of the Seine would at first promote scour, and increase 

 the depth in that part of the channel, and for a little distance above and below. 

 This contraction, however, would impede the influx of the flood tide, and cause 

 changes in the velocity of the current through the narrow neck, and in the wide 

 estuary above, promoting the deposit of silt brought in by the tide. This accretion 

 would be greatly aided by the prolongation of the training walls to Honfleur, so 

 that eventually the greater portion of the estuary comprised between Tancarville, 

 Hoc Point, and Honfleur would be raised to high-water level. This large reduction 

 in tidal capacity would reduce the tidal current through the narrowed entrance, and 

 consequently dimmish again the depth in the channel. Moreover, this reduction of 



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