Ariver is defined as any natural stream of water that flows in a channel with defined banks (Encyclopedia Britannica). The source of a river may be a lake, a spring, or a collection of small streams, known as headwaters. From their source, all rivers flow downhill, typically terminating into the sea/ocean as sketched in Figure 1. In some cases a river flows into the ground or dries up completely before reaching another water body. River is a component of the water cycle. Most rainfall on land passes through a river on its way to the ocean. Smaller side streams that join to a river are tributaries. Usually larger streams are called rivers while smaller streams are called creeks, brooks, rivulets, rills, and many other terms, but there is no general rule that defines a river. Locally, besides sungai, there are also many other terms referring toriver; including alor (Kelantan), carok (Kedah), parit (Johor), batang (Sarawak) and terusan.
Section 5 (Interpretation) of the National Land code: “River” means any stream, creek or other natural watercourse, and any tributary, distributary or artificial deviation thereof.
In Malaysia, the water within a river generally originates from precipitation through surface runoff, groundwater recharge (as seen at base flow conditions / during periods of lack of precipitation) and release of stored water in natural or man-made reservoirs, such as wetlands, ponds or lakes. A river conveys water by constantly flowing perpendicular to the elevation contours, thereby converting the potential energy of the water into kinetic energy. Where a river flows over relatively flat areas, the river will meander, start to form loops and snake through the plain by eroding the riverbanks.
Sometimes the river will cut off a loop, shortening the channel and forming an oxbow lake from the cut off section. Rivers that carry large amounts of sediment develop complex deltas at their mouths, with saline tidal waters forming estuaries.
Definitions of River Basin
"River basin" is an area of land from which all surface run-off flows through a sequence of streams, rivers and, possibly, lakes into the sea at a single river mouth, estuary or delta.