Principles of training Hirers through Tidal Estuaries. 515 



through the outlet and the ebbing current from the trained channel, 

 aided by the accretion of sand in the sheltered recess behind the break- 

 water, led eventually to the formation of two almost rectangular bends 

 in the channel, one just beyond the training walls, and the other near 

 Hoc Point in the model. This tortuous channel, moreover, was 

 shallow, except at the bends and the outlet ; and a bar was formed a 

 short distance beyond the outlet. The contraction of the mouth of 

 the estuary by the breakwater interfered so much with the influx of 

 the tide into the estuary as to render it impossible to raise the tide 

 inside to its previous height ; and the reduction in height of the tide 

 was clearly marked at Tancarville Point in the model. Sediment 

 accumulated in the estuary beyond the trained channel, being brought 

 in by the rapid flood current, and not readily removed by the ebb, 

 except in the trained channel and near the outlet ; and this accretion, 

 by diminishing the tidal capacity, gradually reduced the current 

 through the outlet, and consequently the depth of the outlet channel. 

 A considerable accumulation of sand took place outside the break- 

 water, along the southern sea-coast, so that the bank opposite 

 Trouvilte in the model was connected with the shore, and the 

 foreshore advanced towards the end of the breakwater (Plate 2, 



%. i). 



Scheme B. -The second arrangement of training walls inserted in 

 the model, below Berville, was taken from a scheme proposed in 1888, 

 representing a modification, by another engineer, of the design from 

 which Scheme A was copied.* It comprised the retention of the break- 

 water from Villerville Point to the Amfard bank, the most essential 

 feature in Scheme A ; but the extension of the northern training 

 wall was dispensed with, whilst the southern training wall was pro- 

 longed, in a continuous curve, from Berville to Honfleur (Plate 2, 

 fig. 2), and eventually to the Amfard bank, connecting it there with 

 the extremity of the breakwater (Plate 2, fig. 3). A slight widening 

 Tout of the existing trained channel, by an alteration of the end portion 

 of the northern training wall, completed the arrangement of the 

 model. The results obtained by inset-ting the training wall down to 

 Honfleur, and then working the model for about 3500 tides, are 

 shown in Plate 2, fig. 2 ; and those obtained after the prolongation 

 of the southern training wall to the breakwater, and working the 

 model for about 3700 tides, are shown in Plate 2, fig. 3. The channel 

 followed pretty nearly the concave line of the prolonged southern 

 training wall, between Berville and Honfleur in the model, except 

 near Berville : but the depth of water was less regular than in the 

 previous experiment, owing to the diminished concentration of the 

 ebb from the absence of the northern training wall. The channel 



* ' Memoires de la Societe des Ingenieurs Civils/ Mars, 1888, Paris, pp. 257 and 

 273, and Plate 162, fig. 2. 



