the right bank. Henceforth for the sake of convenience I shall call them the North, Middle, and South Channels.
The silting up of a river's mouth is due to the loss of velocity in its current when the water gets into the wide opening at its junction with the sea and causes the silt to deposit there. The remedy is to maintain the velocity of the current by narrowing the mouth of the river so that it equals that of the upper part. In this way the silt is suspended in the water moving on into the deep sea. The narrowing process may be accomplished by walls or training jetties. And thus the silt may be carried by the water into the deepest part of the open sea and before it settles down upon the bottom a returning tide will carry it from the approach into the shallow parts on both sides of the river's mouth. The mouth of a river can be kept clear from deposit of silt by the action and reaction of the ebb and flow tide. The conservancy of an estuary of any river is accomplished by utilizing these natural forces.
In order to regulate the estuary of the Yangtze we have to study the three channels which form its mouth and to find out which of these channels is to be selected as the regulated entrance into the sea. In Mr. Von Heidenstam's proposal for the improvement of the approach of Shanghai Harbor, he recommends two alternatives, viz., either to block up the North and Middle Channels and to leave the South Channel only for the mouth of the Yangtze, or to train the South Channel only and leave the other two alone. For the present, he
