types of rivers

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The hydrologic cycle

ga.water.usgs.gov/edu/charts/waterdistribution.gif

Types of Rivers

• Rivers are very dependent on climate and their characteristics are closely related to the precipitation and evaporation regimes in their drainage areas.

• Four types:– Perennial or permanent rivers– Periodic rivers– Episodic rivers– Exotic

www.aquatic.uoguelph.ca/rivers/chintro.htm

Permanent / Perennial Rivers• Rivers that flow all year e.g. Orange (Gariep), Kunene, Zambezi.• River channel reaches water table throughout the year.• Orange River used to be non-perennial before the construction of

the Gariep Dam.

Periodic / Non-Perennial Rivers• Only flow during the rainy season e.g. Berg River (seen below)• Water table must rise enough to feed the river when it is not raining

Episodic Rivers• Only flow for short periods after heavy rain e.g. Nassob (Namibia).• May have some permanent pools where bed intercepts water table.• It is an important water source in desert regions.

Exotic Rivers• Rise in humid areas with high rainfall and flow through dry areas.• Gariep river rises in the Drakensberg moutains (high rainfall) and

flows through the Northern Cape (dry region).

Relationship between the water tables and types of rivers Schuters: Pg.155

Orange River Rivers

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Drainage Patterns

Schuters Pg.150 and 151

Dendritic drainage pattern

•Occurs in regions where the rock is uniform in its resistance to erosion.

•Shaped like the branches of a tree.

•Consequent and subsequent streams meet at acute angles.

Rectangular drainage pattern

• Rectangular drainage patterns have rt.-angled bends in the tributaries and the main streams.

• Streams are not parallel to each other.

Rectangular drainage pattern

Trellis drainage pattern

• Occurs in regions the sedimentary rock is folded or where there are alternate layers of hard and soft rock.

• The main stream and tributaries join at rt. angles.

• Streams are parallel with short tributaries.

Trellis Drainage Pattern

Radial drainage pattern

• The stream flows down a dome shaped feature e.g. an isolated hill \ volcanic dome \ spitskop.

Deranged drainage pattern

• A deranged pattern is found in a region that is geological young.

• Haphazard shape.

• Streams entering lakes and marshes in a haphazard pattern.

• Common drainage patterns that are structurally controlled

Superimposed (Inherited) Streams / Drainage

A stream establishes its course in rock layers.

The covering rock is removed and the stream imposes its course on underlying rock of a completely different structure.

River is younger than the structures they flow through.

E.g. The Vaal river in the vicinity of Parys (in the Free State) breaks through two quartzite hills instead of following a course around them.

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 14b–20

Figure 14-12a Superposed Streams


Figure 14-12b Superposed Streams (cont’d)


Figure 14-12c Superposed Streams (cont’d)

Source: Jeff Lepore/Photo Researchers Inc.

Antecedent Streams / Drainage

A stream existed on an earlier landscape which was subsequently raised.

The stream was able to maintain its original course in spite of uplift (or the formation of a mountain or a ridge).

Antecedent streams are therefore older than the structures they flow through.

e.g. The lower part of the Orange river retained its course and eroded downwards at the same rate that the mountains of the escarpment formed.

The stream cut through the obstruction as it formed.


Figure 14-13a Antecedent Streams


Figure 14-13b Antecedent Streams (cont’d)

Superposed Stream

Development ofWater gap

Folded Units

Erosion and downcuttingthrough younghorizontal units

Identify this Stream Pattern

Superimposed and Antecedent Streams

• Superimposed streams is one whose valley and direction of flow were developed much later than the underlying structure, and the river possessed sufficient stream power to cut through these underlying structures.

• An antecedent stream is one whose path of flow within a valley was established before the mountainous structure was uplifted

Schuters Pg.174

Schuters pg 179

Schuters pg 179

Drainage Basin Development

Schuters Pg.151*

Answers

1) Trellis

2) Dendritic

Tree pattern, tributaries joins main stream at acute angles..

Activity 13: Identifying drainage patterns Pg.135

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River Channel Patterns / Stream flow characteristics

Identify the stream flow characteristic of the following river:

Meandering Stream

River winds from side to side

River flows over loose silt and clay

The banks are fairly stable

The river starts to wind due to irregularities in the channel (corkscrew action)

Lateral shifting takes place (meanders shift downstream)

Fastest flow speeds occur on the outer bank (undercut slope) resulting in erosion

Slowest flow occurs on the inner bank (slip-off) slope resulting in deposition

Schuters: Pg.170

Features of erosion and deposition

Schuters: Pg.170

Click here for animation

1) Describe what happens on the outside of the bend2) Describe what happens on the inside of the bend3) What causes the corkscrew motion?

Meandering rivers

http://www.aquatic.uoguelph.ca/rivers/chphys.htm

A meander becomes more pronounced as the streamline shifts between the river banks.

Formation of an oxbow lake

• Small meanders– steep gradient– coarse particles

Gradient

• Big meanders– gentle gradient– fine particles

Meanders in the Amazon Basin

McKenzie River meanders and glacial lakes


Braided stream

The velocity of the river is reduced and this causes the river to split and rejoin many times The river flows over loose sandy alluvium

The banks of the river are unstable and lateral erosion occurs easily As a result of the wide channel, the river flows slowly and large deposits of alluvium form islands in the middle of the river.


• Braided Pattern = steep slope + high stream power + coarse bed materials changes to gentle gradient and slows down depositing material

Braided channel

earthsci.org/teacher/basicgeol/stream/stream.html#Erosion%20by%20Streams

Braided River

Braided geometry, Matanuksa River, Alaska

Braided River, Shyok River, India


Straight Stream

Rock-controlled channel

o The river flows in straight and twisting sections

o It is characterized by many rocky banks, rapids and waterfalls

o The rock barriers on the sides and riverbed prevent the river from determining its own channel pattern


Identify the drainage pattern and describe the underlying topography.

types of rivers

Education

stream pattern

antecedent streams drainage

orange river rivers

types of rivers rivers

drainage patterns schuters

stream river winds

inherited streams drainage

trellis drainage pattern