Three compartments are pointed out as existing in all rivers, when viewed in connection with the sea, possessing different characteristics, and requiring different classes of works for their improvement. These are, first, The “sea proper,” characterised by the presence of unimpaired tidal phenomena, and including all works connected with the improvement of bars. Second, The “tidal compartment of the river,” characterised by the modified flow of the tide, produced by the inclination of the bed, and embracing works connected with the straightening, widening, or deepening, of the beds of rivers; the formation of new cuts; the erection of walls for the guidance of tidal currents, and the shutting up of subsidiary channels.