GEO1/6: DRAINAGE PATTERNS

This unit is Drainage patterns which is plan layout made by a River and its tributes.

DRAINAGE PATTERNS

A drainage pattern is the plan layout made by a River and its tributes.

The drainage pattern of a river determined by many factors i.e. the slope of the land, the nature of the soil, the nature of the rocks over which the river is flowing and the structure of the rock.

There are many types of drainage and among these we have:

Radial drainage pattern

Trellis drainage pattern

Dendritic drainage pattern

Centripetal drainage pattern

Rectangular drainage pattern

Superimposed drainage pattern

Annular drainage pattern

Antecedent drainage pattern e.t.c.

RADIAL DRAINAGE PATTERN

This drainage pattern is the one that has one source with very many rivers originating from it down a conical hill.

This drainage pattern is connected to the slope of the land which must be conical and gently sloping.

This type of drainage has a small catchment area and it is mainly found in areas where Vulcancity took place i.e. on Mt Elgon i.e. in Sironko Koitabura in Eastern Uganda.

The diagram below shows the Radial drainage pattern. Mt Kilimanjaro, Mt.Rwenzori has rivers like Mubuku, Nyamwamba, Lume Mt. Kilimanjaro has rivers like Isavo, sagari, Kathita.


TRELIS DRAINAGE PARTTERN

This is a pattern whereby the tributaries join the main river/stream at approximately right angles. This drainage pattern is very common in areas where the rocks are jointed or faulted or rocked. The diagram below shows the trellis drainage pattern.

Examples include River Aswa, River Kagera, River Tochi, River Mava, Aworango, River Mlovoni Tz.

DENDRITIC DRAINAGE PATTERN

It’s a plan made by a River where by the tributaries join the mainstream at an acute angle. This drainage pattern resembles a tree with its branches.

The diagram below shows a dendritic pattern.

 

CENTRIPETAL DRAINAGE PATTERN

This is the pattern in which rivers flow from all directions towards the common point pattern of their type is rare, all that is known about them is that they can form in ares that have:

Rimmed plateau surface

Experienced lava damming

Tilted slopes

Experienced down warping.

Through rare there are some few examples are found in E.A. They include the river systems of Lake Turkana in northern Kenya, Rukwa in southwestern Tanzania and Baringo in central Kenya.

 

RECTANGULAR DRAINAGE PATTERN

It has a similar plan as the trellis i.e. both the mainstream and its tributaries from right-angled bends.

This reflects marked control exerted by joint or fault systems because the streams tend to follow joints or fault lives in the rock.

They differ in the ways of form. Examples include sunburn areas in Kenya, the Nyika around Maji ya chumui.

It develops in areas affected by earth movements i.e. where faulting took place and in most cases they are found in fault guided valleys e.g. of such pattern are seen on Athil River draining into lake Baringo, Aswa River, River Pangani at the foothills which pare hills in North Tanzania and the upper Nile near lake Albert.

It differs from the trellis in that the tributaries of the rectangular drainage pattern make sharp bends along their course and the minor tributaries flow almost parallel to the mainstream.

SUPERIMPOSED DRAINAGE PATTERN

It describes a river valley on part of a valley that developed on former layer of rocks and is now superimposed onto a previously buried and completely different rock structure to which its discordant.

Such river valleys are younger in age than the structure on which they are flowing. In most cases, the remnants of the former rock cover are tilt to be seen on either side of the river valley.

ANNULAR DRAINAGE PATTERN

This is when the tributaries joint at sharp angles to the mainstream and are arranged in such a way that they form a series of curves about a dissected dome basin or a crater area. Their form depends upon the following factors

The presence of a crater

The dome-like feature that may be composed of alternating hard and soft rock which appears in a concentric curve that have been dissected by the streams, lake Ngozi in Tanzania where calderas and expression crater form a circular drainage pattern.

ANTECEDENT DRAINAGE PATTERN

It describes a river valley or part of a valley that developed on a former landscape which was later uplifted by local earth movements, but which was able to maintain its course by recording vertically at a rate at fast enough the keep place with the rising land.

In actual sense, such valleys are in most cases older in age than the structure to which they are discordantly areas of fairly recent earth movement such as the young fold mountains.

The great Ruaha river North East of Iringa between Utera and Kidaku, where it cuts through the southern highlands there are series of antecedent gorgers with numerous rapids.

A video showing a Rectangular Drainage Pattern

Conditions

Rainfall must be reliable and a lot for the continuous flow of the streams.

Large catchment area

Rocks with alternating Resistance

It can exist in areas where River capture has taken place.

PARALLEL DRAINAGE PATTERN

This is a pattern that develops in areas with alternating hard and soft rocks. These rivers will create their own valleys within the soft rocks and they will be separated by the bands and hard rock and as a result, they will be moving parallel flowing to each other and in the same direction hence the name.

There are parallel drainage patterns on the Eastern slopes of Abadeya Ranges western part of Mau ranges in Kenya, Ethic rives, Nairobi River, Rwiru rivers and Komu rivers in Kenya.

The conditions which lead to the form of this drainage pattern are:

There must be alternating hard and soft rocks that are parallel to each other and have the same direction of drip.

There must be a lot Rainfall for the river to maintain their direction of flow (2 exist) the diagram below show the parallel drainage pattern.

PINNATE DRAINAGE PATTERN

Under this layout, the tributaries join the main river at extremely acute angles, forming something like a feather these are found in Kerio valley in Kenya where they are very many minor tributaries joining the main river.

This drainage pattern is found within the secondary rifts within Kenya.

This drainage pattern develops in areas that experience a lot of rainfall and also the rocks within these areas must be gently dipping with uniform resistance.

This is common in those areas.

ACCORDANT DRAINAGE PATTERN

Here, flow of the main river and their tributaries are determined b the underlying rock structure.

The river and its tributaries flow along easily evoked rocks avoiding hard rocks or resistant rocks. Many drainage patterns are accordant because their direction of flow is dictated by the rock structure (nature of the rock)

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ASSIGNMENT : DRAINAGE PATTERNS Assignment MARKS : 10  DURATION : 1 week, 3 days

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