Principles of training Rivers through Tidal Estuaries. ,513 



inserted in sections ; and the model was worked between each addition, 

 to conform, as far as practicable, to the actual conditions. The fine 

 particles of the sand accreted behind the training walls ; and the 

 channel between the walls was scoured out, corresponding precisely 

 to the changes which have actually occurred in the estuary of the 

 Seine. The foreshores at the back of the training walls were raised 

 up in some parts to high-water level, whilst in other places the 

 accumulation was somewhat retarded by the slight recoil of the water 

 from the vertical sides of the model, and by the wash over the vertical 

 training walls, these forms being necessitated by the great distortion 

 of the vertical scale of the model. On the whole, however, the 

 accretion and scour in the model correspond very fairly to the results 

 produced by the existing training walls in the estuary. The accretion, 

 moreover, in the model, extended beyond the training walls on each 

 side, down to Hoc Point on the right bank, obliterating the inshore 

 channel close to Harfleur, which had been reproduced in the model, 

 and down to Honfleur on the left bank, corresponding in these 

 respects also to the actual changes in the estuary.* The main 

 channel also, beyond the ends of the training walls, was compara- 

 tively shallow, and was unstable, reproducing the existing conditions 

 in the estuary. 



The experiments relating to this stage extended over a year and a 

 half, taking up all the time that could be spared to them by myself 

 and my assistant during that period ; they formed the turning point 

 of the investigation, and have the interest of being, as far as I am 

 aware, the first attempt at putting training walls in a model, and 

 obtaining the resulting accretion on a small scale. Without the 

 accomplishment of this stage, it would have been useless to continue 

 the investigation ; and its satisfactory attainment proved so difficult 

 in actual practice, that for a long time it seemed probable that the 

 attempt must be abandoned. 



Application of System to Ascertain the Probable Effects of any 

 Training Works. As the first and second steps in the investigation, 

 by the aid of the model, had furnished results which corresponded very 

 fairly with the actual states of the estuary of the Seine before and 

 after the execution of the training works, the final stage of the 

 investigation, for ascertaining the probable results of any extensions 

 of the training walls, could be reasonably entered upon. In selecting 

 the lines of training walls to be experimented on, it appeared ex- 

 pedient to adopt those which have been designed, after careful study, 

 by experienced engineers, both on account of the results from these 

 being far more interesting than those of a variety of theoretical 

 schemes, and also in the hope that some assistance might thereby be 

 rendered to French engineers in the prosecution of this important 



* ' Instit. Cir. Engin. Proc.,' vol. 84 ; compare Plate 5, fig. 1, and Plate 4, fig. 1. 



