ON THE ACTION OF WAVES AND CURRENTS. 529 
In Tank F’ the sand was laid similar to that in Tank E, the rise of tide 
0:1 foot, and the mean tide 9-006 foot above the level of the sand. The 
period being 30:04, land water, 1/200 the capacity of the estuary, was 
introduced at the top of the river. 
In starting these experiments the effect of the tidal river was very 
marked. After the first tide in Tank E some depth of water remained 
in the river and a long way down the estuary at low water, and the tide 
came up with a bore increasing in height all the way to the top of the 
river, and then returned with a bore to the lower end of the river. The 
bore, as before, soon died out over the greater part of the estuary as the 
sand at the bottom became lower. And the bore gradually died out in 
the top of the V until as the number of tides approached 16,000 the bore 
only began to show at about Section 4 and ran up the river very much 
diminished from what it was originally. 
Owing to the indraught and outflow of the river, the velocity of the 
water and its action on the sand was greater at the top of the V and the 
mouth of the river than at any part of the estuary, while for some way 
up the river and all the way down the estuary there was a large volume 
of water running at low water. The top of the river was ninety miles 
(reduced to a 30-foot tide) from the bottom of the estuary, and the tide 
did not commence to fall at the top of the river until after low water at 
the mouth, so that nearly all the tidal water in the river ran over the 
estuary during the low water. The delay in the return of the water from 
the river obviously played a most important part in the effects produced.. 
At the bottom of the estuary the sand came down much as usual, but, 
it did not rise at the head of the estuary. For the first 10,000 tides the- 
sand was all covered at low water and rippled with active ripples up to. 
the end of the river, and it seemed as if no banks were going to appear. . 
The sections of the sand appeared as nearly as possible horizontal. The- 
level having lowered from the bottom of the estuary up to Section 15, 
from Section 15 to Section 3 it was somewhat raised, then from 3 up- 
wards to 7 it was lowered, and thence up to the top of the river it was.. 
raised in a gradual slope. At about 12,000 tides two small banks ap- 
peared at low water, one on each side of the estuary at Section 13. 
Everything was perfectly symmetrical so far, but from this time the bank 
on the right of the estuary extended downwards, while that on the left . 
extended upwards and a depression or channel formed between them. 
extending across the estuary in a diagonal manner. This was the con- 
dition when at 16,000 tides the first survey was made. 
As the running continued these banks continued to rise, that on the- 
right downwards, that on the left upwards, until a distinct channel was. 
formed from the mouth of the river down to Section 20, as shown in the. 
second survey at 32,000 tides. 
The level of the sand at the mouth of the river altered very little, 
diminishing during the first 10,000 tides and then reassuming its original 
height, but the sand passed upwards through the mouth and gradually. 
raised the level in the river above until there was only about 0:02 foot in 
the shallowest places at low water (corresponding to 5 foot on a 30-foot 
tide) ; this level was first reached at the top of the river and then grada- 
ally extended down to Section 19, which point it had reached at 32,000, 
tides when the second survey was taken. In this condition the bore still 
reached the end of the river, raising the water 0:02 foot (5 feet on the 
ier ee Fae Above Section 19 all motion of the sand had ceased, but 
. MM 
