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In this lesson we are going to discuss the continuation of river deposition features

Answer Text:
River Braids

- Network of diverging and converging channels along a rivers course.
Factors favouring formation of braids
a) River must be carrying large load.
b) Reduced gradient on the section.
c) Reduced amount of water such as in dry season or arid conditions.
d) Presence of obstacles such as rock out crops.
Formation
- River flows sluggishly due to low gradient.
- Deposits of alluvium are laid on river bed.
- The deposits raise the river bed causing the channel to be subdivided into channels or distributaries.
Natural Levees

- Raised river banks which are made of alluvial materials.

Formation
- River floods and spills over its banks.
- Deposition of coarse materials near the banks and fine materials are carried further on the flood plain.
- Coarse materials accumulate raising the banks above the general level of the flood plain.

Effects of Levee Formation
a) Creation of differed tributaries and confluences.
Differed tributary: Tributary blocked from joining the main river by levees.
Differed confluence: New point where the differed tributary joins the main river downstream.
b) Destructive flooding.
- Due to the river bursting its banks during the flood season due to the bed being raised above the general level of the
flood plain.
- Due to differed tributaries flowing into the flood plains.
- Because the river channel has become narrower and shallower due to deposited alluvium.

Estuaries
- Broad channel at the mouth of a river where the river enters the ocean as a whole.
- Some are deep and narrow because sediments are carried away by ocean currents while others are wide and shallow due
to sediments covered by water e.g. on R. Congo and Gabon.

Deltas
- Low lying tract of alluvial deposits formed at the river’s mouth.
Ideal Conditions for Formation of A Delta
At A Rivers Mouth
1. Large load such as from a large catchment area where erosion is taking place actively.
2. The rivers course to be free from obstacles such as swamps so as not to filter sediments before they reach the mouth.
3. Low speed at the point where the river is entering a sea or lake for deposition to take place.
4. The rate of deposition should be higher than the rate of erosion by sea or lake currents.
How a Delta Forms
- The speed of the river is
checked by sea or lake.
- Heavy load is first deposited.
- Lighter load is carried further
into the sea causing that part of
the sea to become shallower.
- The part is colonised by plants
making it swampy but firmer.
- Plants trap more alluvium
making the delta to grow in
height.
- The river builds levees
making it narrower.
- The river burst its banks and
small channels branch off the
main river and carries water
into the sea or lake
(distributaries).
Types of Deltas
1. Marine: Type formed at sea.
2. Lacustrine: at a lake.
3. Inland Delta: Deltas which
form along a rivers course before it reaches the lake or sea.
Formation
- The velocity of the river is checked on entering a relatively flat swampy land.
- The river builds up levees.
- The river bursts banks forming distributaries.
- Alluvial deposits are spread over vast areas when river floods e.g. Niger and Okavango deltas.
4. Arcuate Delta

- A delta with a convex shoreline on the seaward end due to strong currents spreading materials over a wide area on seaward side.
- Has many distributaries e.g. Tana and Rufiji deltas.
5. Birds Foot Delta

- Type of a delta with a pattern resembling the foot of a bird.
- Has few distributaries.
- Formed on a river carrying large quantities of fine alluvium into water where there is low wave energy e.g. Omo and
Mississippi deltas.
6. Estuarine Delta

- Delta which has formed on an estuary.
Formation
- The rivers load is deposited on the estuary when the speed is checked by sea.
- The river cuts across in a single channel that may be bordered by levees e.g. on R.Volta in Ghana and on R. Zambezi.