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Adistributary, or adistributary channel is astreamchannel that branches off and flowsaway from a main stream channel. It is the opposite of atributary, a stream that flowstowards and into another stream or river. Distributaries are a result ofriver bifurcation and are often found where a river approaches alake or anocean and divides into distributary networks; as such they are a common feature ofriver deltas.[1] They can also occur inland, onalluvial fans, or where a tributary stream bifurcates as it nears itsconfluence with a larger stream. In some cases, a minor distributary can divert so much water from the main channel that it can later become the main route.
Common terms to name individual river distributaries inEnglish-speaking countries arearm andchannel. These terms may refer to a distributary that does not rejoin the channel from which it has branched (e.g., the North, Middle, and South Arms of theFraser River, or the West Channel of theMackenzie River), or to one that does (e.g. Annacis Channel and Annieville Channel of theFraser River, separated byAnnacis Island).
In Australia, the termanabranch is used to refer to a distributary that diverts from the main course of the river and rejoins it later. InNorth America such a branching river is called abraided river.[2]
InLouisiana, theAtchafalaya River is an important distributary of theMississippi River. Because the Atchafalaya takes a steeper route to theGulf of Mexico than does the Mississippi, over several decades the Atchafalaya has captured more and more of the Mississippi's flow, after the Mississippi meandered into theRed River of the South. TheOld River Control Structure, adam which regulates the outflow from the Mississippi into the Atchafalaya, was completed by theArmy Corps of Engineers in 1963. The dam is intended to prevent the Atchafalaya from capturing the main flow of the Mississippi and stranding the ports ofBaton Rouge andNew Orleans.[3]
InBritish Columbia, Canada, theFraser River has numerous sloughs and side-channels which may be defined as distributaries. This river's final stretch has three main distributaries: theNorth Arm and theSouth Arm, and a few smaller ones adjoining them.
Examples of inland distributaries:
TheCasiquiare canal is an inland distributary of the upperOrinoco, which flows southward into theRio Negro, forming a unique naturalcanal between the Orinoco andAmazon river systems. It is the largest river on the planet that links two major river systems.
TheHuai River in China splits into three streams. The main stream passes through the Sanhe Sluice, goes out of the Sanhe river, and enters theYangtze River throughBaoying Lake andGaoyou Lake. On the east bank ofHongze Lake, another stream goes out ofGaoliangjian Gate and enters theYellow Sea at theport of Bidan through Subei Guan'gai Zongqu, the mainirrigation channel of NorthernJiangsu); its total length is 168 kilometers. The third stream leaves the Erhe lock on the northeast bank of Hongze Lake, passes the Huaishuhe River to the north ofLianyungang city, and flows into Haizhou Bay through the Hongkou.
TheTha Chin River andNoi River are distributaries of theChao Phraya River inThailand, splitting off from the latter about 200 kilometers upstream from theBay of Bangkok.
TheBrantas River inEast Java,Indonesia, branches off into two distributaries,Mas River, also known as Surabaya River, andPorong River.[4]
TheHong River inNorthern Vietnam has notable distributaries such as theDay River,Ninh Co River and the Luoc River. All of these rivers empty into theGulf of Tonkin.
A number of the rivers that flow inland from Australia'sGreat Dividing Range form distributaries, most of which flow only intermittently during times of high river levels and end in shallow lakes or simply peter out in the deserts.Yarriambiack Creek, which flows from theWimmera River into Lake Coorong, and Tyrrell Creek, which flows from theAvoca River intoLake Tyrrell, are two distributaries inVictoria. TheNarran River flows from theBalonne River inQueensland intoNarran Lake inNew South Wales.
Many of Papua New Guinea's major rivers flow into theGulf of Papua through marshy, low-lying country, allowing for wide, many-branched deltas. These include theFly River, which splits into three major and several minor rivers close to its mouth. TheBamu River splits into several channels close to its mouth, among them theBebea,Bina,Dibiri, andAramia. TheKikori River also splits into a multitude of channels as it crosses the plains close to the Gulf of Papua. ThePurari River splits into three major channels as it approaches its mouth.
New Zealand's second-longest river, theClutha River, splits into two arms, theMatau and theKoua, some 10 kilometres from the South Island's Pacific Coast. A large island,Inch Clutha, lies between the two arms. Many of the rivers crossing theCanterbury Plains in the central South Island arebraided rivers, and several of these split into separate branches before reaching the coast. Notable among these is theRangitata River, the two arms of which are separated by the low-lyingRangitata Island.