RIVER AND RIVER ENGINEERING. A river is any natural stream of fresh water, larger than a brook or creek, which flows in a well-defined channel. Usually it discharges into another and larger body of water, the ocean, a lake, or another river. In rare instances in regions of porous soil it soaks into the ground, or, in excessively arid regions, evaporates, in which case it becomes a "lost river." In other regions of favourable rock conditions it may also run under ground for certain distances, disappearing and reappearing one or more times. A river with a well-cut channel and a graded bed, usually reaching base-level at its mouth, is an adolescent river. Rivers as they grow older usually widen their valleys accordingly unless prevented by certain geological forma tions or occurrences. A river whose upper waters sometime in the past suddenly found a new outlet, diminishing the volume and force of the original river and also its length, is known as a be headed river. For other facts relating to the origin and subsequent development of rivers and their valleys see GEOGRAPHY and GEOLOGY.
The river works which the engineer may be called upon to execute vary widely in their character and object. The more im portant of these which are described in the present article may be grouped under the following heads :—(i) The prevention of river inundations and the mitigation of their effects ; the improve ment for navigation of the non-tidal portions of rivers; and (3) works for the improvement of navigation in the tidal compart ments of rivers, in their estuaries, and at the outlets of rivers flowing into tideless seas.
Other river engineering works are dealt with under separate headings, for instance, the utilization of river waters for power production (see ELECTRICAL POWER GENERATION : Hydroelectric Generation; etc.) ; works for water storage and supply for vari ous purposes including irrigation (q.v.) ; works connected with fisheries (q.v.) ; and reclamation of land (see COAST PROTECTION AND RECLAMATION). See also the articles on HYDRAULICS, CANALS AND CANALIZED RIVERS, WEIR, and particular rivers, e.g., MISSIS SIPPI and DANUBE.