Drainage refers to all surface water like lakes, rivers, swamps etc. in many parts of east Africa. Faulting has had a great significance on the flowing rivers and on the drainage systems as seen below.
Vertical faulting across a river valley may cause the occurrence of water falls, rapids and other related features such as plunge pools. A water fall is a sharp break in the channel gradient over which water flows. Examples in east Africa include the Murchision falls, kisizi falls etc. it can be illustrated as below.
Faulting has resulted into the formation of grabens or rift valley lakes. Grabens develop with in the rift valley floor after secondary or further faulting on the rift valley floor. When the resultant depression is filled with water, it then forms a rift valley lake. This has therefore accounted for water surfaces like lake Edward, albert, Tanganyika, Malawi, Turkana among others. These lakes are usually elongated, deep, narrow and steep sided. It can be illustrated as below.
Faulting has also led to the development of fault guided river valleys for example river Aswa in Acholi land in northern Uganda. During faulting, the faulted zones became more prone to weathering and erosion. A valley was curved out following the fault line in which a river passed leading to the formation of a fault guided river valley. It can be illustrated as below.
Horizontal or lateral displacement of tear faulting across a river may cause a river to be offset at the point it crosses a fault as shown below.
Faulting has also resulted into the formation of tilt block lakes. A tilt block is a steep slope where land falls from a higher elevation to a lower elevation. Its formed when one side of the fault is uplifted higher than the other. When tilting occurs, the top part of the block will not be flat but instead inclined or tilted. The middle block then becomes a tilt block. The depression may be filled with water to form a tilt block lake for example lake olbolsat.
Faulting has also indirectly affected water surfaces through creation of block mountains. These mountains experience frequent orographic rainfall and are sources of rivers. Block mountains are characterized by radial drainage whose subsequent streams also develop dendritic patterns for example on mountain Rwenzori rivers like Mubuku, Mpanga, Sebwe, Nyamwamba among others are radiating from its top creating radial drainage system and as they flow downstream, their subsequent streams have resulted into dendritic drainage patterns or systems for example river Nyamwamba
Faulting in conjunction with warping, resulted into the formation of open enclosed basins e.g. Lake Victoria and Kyoga which were as a result of these processes. After the formation of the Victoria basin by down warping, the rivers that were flowing westwards into the Congo basin for example Kagera and Katonga all were reversed into the basin forming Lake Victoria.
The up thrust in western Uganda led to the formation to the formation of Rwenzori mountains and it was followed by a slight up thrust in the east making the rivers that were flowing east wards to also flow back into the basin. These included river Mara, Nzoia eventually leading to the formation of Lake Victoria and kyoga.
Today much of Lake Victoria is a vast shallow depression of papyrus swamps and its peculiar outline is due to river kafu being forced to flow back into its own valley and tributaries. Therefore, it’s important to rule that crustal warping (up warping) across a river valley will gradually force a river to reverse its direction of flow and run back if its unable to maintain its original flow.
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