LANDFORMS CAUSED BY RIVER DEPOSITION

  •  Leeves

  • Differed tributaries

  • Braided channels

  • Flood plains

  • Ox bows

  • Alluvial funs

  • Deltas

LANDFORMS CAUSED BY RIVER DEPOSITION

Leeves

Leeves are exercised banks built by a river on the sides of the channel. They are usually only about one-meter high. When a river floods, the water level rises and it over flows its channel. Friction between the water and the banks causes the river to deposit its load to form a raised bank known as a leeve. They usually encourage the formation of swamps in the flood plain since not all the water is able to return to the main channel when the floods subside eg leeves are found along river Malaba in eastern Uganda.

Differed tributaries.

When leeves are formed on the banks of a river, they make it difficult for the tributaries to join the river they therefore flow by the sides of a river for several kilometers. They are therefore known as deferred tributaries and where they join the river is known as deferred confluence.

Braided channel

This refers to a wide, shallow river channel in which the river divides and subdivides itself into a number of interconnecting channels separated by sand banks and islands of alluvium. The sand bars and main channels may disappear during floods since they sub merge.

River braiding occurs after the deposition of large quantities of course materials eg sand and gravel on the river bed. These gradually increase and form islands which the river dodges by subdividing into small channels hence forming braided river streams.

Meanders

These are curved bends of a river’s channel which continuously swing from side to side in wide loops. They form in both the mature and the old stage of a river. Meanders are largely due to the river’s load its carrying and the low gradient which leads to deposition of the load. They are formed by alternate under cutting and deposition leading to formation of concave and convex river bends. The constant erosion of the concave banks which produce a river cliff and the deposition on the concave banks forms a slip off slope.

Best examples can be seen on river Rwizi in Mbarara, R. Mpanga in fortportal, river semiliki etc

Flood plains

This a wide flat plain of slope of alluvium on the floor of a river valley across which a river flows in a meandering / braided channel. In the old stage of a river, the gradient becomes flat or low, the river is carrying a lot of load which forces this river to deposit this excessive load along its channel over which it flows or sometimes dodges. Most flood plains are marshy with several swamps and small lakes.

A flood plain develops through the meandering of a river. As the river swings across the valley, it widens the valley floor. The valley sides and spurs are slowly worn back and with time a line of low bluffs or river cliffs is formed on the either side of the river plain. With time, the valley will become so wide, the alluvium deposited on the meander slip off slopes also called point bar deposits gradually joined up to cover the eroded valley floor with a layer of alluvium hence forming an alluvium plain / flood plain.

Ox- bow

An ox-bow is a horse shoe shaped final section of a formerly pronounced meander which has been finally separated from the main river. If it contains water, it forms an ox-bow lake. Ox – bows are formed along parts of the flood plain where meanders are sharp that only a narrow neck of land remains between the meander loops. During periods of floods, the neck may be broken through and the river may by pass the meander. Its eventually cut off by deposition at the old meander neck. If the ox bow lake is filled with alluvium, it will dry out hence leaving behind a meander scar. Best examples can be found at river Nzoi  and Tana in kenya, River semiliki and Rwizi in western Uganda and R. Rufigi in Tanzania

Alluvial fans

Its sometimes referred to as debris fun. Its defined as a fun shaped deposit left by a river as it emerges from a narrow valley onto a wide gentle plain. As the river flows down there is a sudden decrease in a gradient and an increase in the channel width which causes the river to deposit its load. An alluvial fun is therefore formed and their size ranges from a few meters to several meters. They are similar to deltas except that they are formed on land, examples are found in the Kilombero river valley.

Deltas

A delta is a large flat low lying swampy plain characterized by presence of deposited materials, distributaries, small lakes and lagoons and vegetation and triangular I shape.

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