Principles of training Rivers through Tidal Estuaries. 509 



experiments involving essentially different and novel conditions would 

 lead to any satisfactory results. I therefore restricted the require- 

 ments for my experiments within the smallest possible limits, and 

 contented myself with the simplest means, and the limited space 

 available in my office at Westminster. 



Description of Model of the. Seine Estuary. The model represent- 

 ing' the tidal portion of the River Seine and the adjacent coast of 

 Calvados, extending from Martot, the lowest weir on the Seine, down 

 to about Dives, to the south-west of Trouville, was moulded in Port- 

 land cement by my assistant, Mr. Edward Blundell, to the scales of 

 4"o1roi) horizontal and T ^ vertical. The first is the scale of some of 

 the more recent published charts of the Seine and even at that 

 scale the model is nearly 9 feet long; whilst I made the vertical 

 scale one hundred times the horizontal, as the fall of the bed of the 

 tidal Seine is very slight, and the rise of spring tides at the mouth, 

 being 23 feet 7 inches, amounted to an elevation of the water in the 

 model of only 0'71 inch. There are two banks at the mouth of the 

 estuary, between Havre and Villerville Point, known as the Amfard 

 and Ratier banks, which emerge between half-tide and low water, and 

 divide the entrance to the estuary into three channels. Through all 

 the changes in the navigable channel at the outlet, these banks always 

 appear in some form or other in the low-water charts, either connected 

 with the sandbanks inside the estuary, or detached. On examining 

 the large chart drawn from the survey made by M. Germain in 1880, 

 I found that rock and gravel cropped up to the surface over a certain 

 area on these banks, and accordingly I introduced solid mounds at 

 these places to represent the hard portions of the Amfard and Ratier 

 banks, which are permanent features in the estuary. As a rocky 

 bottom is found near Havre, and also at Villerville Point on the oppo- 

 site side of the outlet, Amfard and Ratier banks are doubtless the 

 remains of a rocky barrier which in remote ages stretched right 

 across the present mouth of the river. Where the rocky bottom lies 

 bare near Havre and Villerville, the model was moulded to the exact 

 depths shown on the chart of 1880 ; but in other places the cement 

 -bottom was merely kept well below the greatest depth the channel 

 had attained at each place, whilst the actual bed of the estuary in the 

 inodel was formed by the now of water over a layer of sand. 

 Arrangements for Tidal and Fresh-water Flow. The mouth of the 

 Seine estuary faces west ; but the tidal wave comes in from the north- 

 west, and the earliest and strongest flood tide flows through the 

 northern channel between Havre and the Amfard bank ; whilst the 

 influx through the southern Villerville channel occurs later, and is 

 stronger towards high water. Accordingly, the tidal flow had to be 

 introduced from a northerly direction, at an angle to the mouth of the 

 'estuary ; and the line of junction of the hinged tray, producing thfe 



