From Gravesend to the Nore is an immense triangular area with sandy bottom, muddy foreshores and several deep channels running in the general direction of the Essex coast line, that is, N.E. to the North Sea. The area may be roughly estimated at 120 square miles, and the navigable depth of the principal channels at from 60 ft. to 26 ft. at low water Spring tides.

The volume of the estuary at high water Spring tides may be taken at 2600 million cubic yards, and at low water Spring tides at 1500 million cubic yards, the volumes of the river from Gravesend to Teddington being respectively 180 million and 80 million cubic yards, so that the volume of tidal water entering the river each tide is about 100 million cubic yards.