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A meander is a winding curve or bend in a river. They are typical of the middle and lower course of a river. This is because vertical erosion is replaced by a sideways form of erosion called lateral erosion, plus deposition within the floodplain.

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A meander is a winding curve or bend in a river. They are typical of the middle and lower course of a river. This is because vertical erosion is replaced by a sideways form of erosion called lateral erosion, plus deposition within the floodplain.

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This refers to the route taken by the river when it flows from its source to its mouth. A river tends to flow faster when it flows over a straight course as it expands less energy since there is less friction to overcome. On the other hand, a river tends to flow slower when a river’s course is winding as it has to expand more energy to overcome greater friction at the bends of the river.

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The river has to overcome friction with the banks and bed of the channel. The shape of the channel or its cross section affects the wetted perimeter. The wetted perimeter refers to the total length of the river sides and bed. The greater the wetted perimeter, the greater the friction between the water and the banks and the bed of the channel, and the slower the flow of the river.

If both channels have the same cross-sectional area, the one with the larger wetted perimeter flows slower than that of a small wetted perimeter because of more friction

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The rougher the river channel, the slower is the river flow. Rock boulders on the river bed and rock outcrops on the river sides increase friction between the water and thus slow down the flow as friction needs to be overcome

On the other hand, a river flows faster, instead, in a channel made of smooth slits and clays

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all rivers have energy.
the energy available determines a river's ability to erode, transport or deposit.

the energy of a river depends on the speed of the water flow or velocity and the volume of the water.

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- Meanders: Loops in the course of the river due to erosional and depositional processes

-River cliff and slip off slopes: as meanders swing from side to side, the higher velocity on the concave bank causes the current from the concave bank to descend undercutting and eroding the concave bank. The eroded material is carried along the bed and up the convex bank where it's deposited

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River has less GPE and more KE so erosion shifts from vertical to lateral erosion
Corrosion is still the main erosive process as large particles are transported by saltation

Avergae load size decreased

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Rock erodes at a slower rate on the more resistant rocks. Faster erosion rates steepen gradient. This speeds up flow of water and increases turbulence creating rapids. When a river flows over an area of alrernating bands of gently inclined resistant and less resistant rocks, the less resistant rock is eroded much faster. The river falls swiftly when it flows over outcrops of the resistant rocks

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this refers to the amount of water in the river.

(a) size of drainage basin

a larger drainage basin → a greater volume of water. this is because there is a greater number of tributaries bringing water to the river resulting in a higher surface runoff.

(b) presence of vegetation cover

thick vegetation cover to intercept rain and allow more water to infiltrate into the soil subsurface and percolate through the underlying soil and rock layers  → less surface runoff  → less water flows into the river  → volume of water would be smaller than that of an area with little or no vegetation

(c) rainfall
higher rainfall → greater volume of flow in a river

(d) temperature
temperature is high  → more evaporation and transpiration  → reduces the amount of water in the river

(e) permeability of rocks
> rocks which allow water to pass either via a network of pore spaces between particles or along bedding planes, cracks and fissures are permeable

water flows through an area of permeable rock → more water infiltrates the ground → low surface runoff → lower volume of flow.

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The speed of flow of a river whose average gradient is steep would be faster than that of a river whose average gradient is gentle.
The gradient of a river is seldom the same throughout its entire course. Gradient decreases downstream. The river usually has a steep gradient near its source and a gentle gradient towards its mouth.
A river flowing down a steep slope or gradient has a higher velocity than one which flows down a gentler gradient.
For example, the speed of flow in a river that plunges down a steep in the form of a waterfall is much higher than the speed of flow in a river that winds its way down a gentle slope

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River velocity varies from time to time and is influenced by several factors; channel shape, river gradient, channel roughness, shape of the river's course and volume of water

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The river mainly transports large piece of angular rock and does so by traction
- increases erosion of bed by corrosion as a result of the load being dragged

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River starts to meander, the channel is wider and deeper than in the upper course

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- depressions in the river bed
- different sizes and ranges from a few centimetres to metres in diameter
- formed by river abrasion
- it carries the load
- pebbles and cobbles are trapped in slight hollows are swirled about
- holes are drilled, enlarged and deepened

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- deposition
- lateral erosion
- suspension

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-the river has a lot of GPE so it has a lot of energy to erode vertically.
-the bed f the river is eroded greatly while the banks aren't eroded as much.

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Characteristics
- a deep narrow valley with steep, almost vertical sides
- develops when a waterfall retreats upstream

Formation
1. Water plunges forcefully over the more resistant cap rock as a waterfall. The impact of the falling water erodes the base of the waterfall, enlarging the plunge pool. The backsplash of the turbulent water at the . base undercuts the cliff face of less resistant rock.

2. Over time, the continuous undercutting of the base causes the cap rock to lose support and collapse.

3. The waterfall retreats upstream and a long narrow, deep valley with almost vertical sides, called a gorge, is formed.

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Open V-shape, wider floor

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-  a series of very short and fast-flowing turbulent falls of water along a part of a river
- water is shallow

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- open/ gentle sloping valley with floodplain
- flat and wide floodplain
- wide, open valley
- very wide and very deep channel

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What is a waterfall?
A waterfall is a sudden and rapid fall (vertical) of the water along the course of the river.

How is a waterfall formed?
1. River flows across alternating bands of more and less resistant rocks.
2. The less resistant rock erodes faster than the more resistant rock --> gradient of the river is changed, forming a slight depression in areas with less resistant rock.
3. Over time, the less resistant rock erodes faster than the more resistant rock, steepening the gradient --> causing a waterfall to be formed.
4. The impact of the falling water causes the base of the waterfall to be eroded via hydraulic action --> deepening the depression --> a plunge pool is formed.

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Waterfall

Gorge

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- oxbow lakes
- flood plaines
- levees
- deltas

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erosion:
- aa the river flows, pieces of rock are removed from the river bed and banks, and moved along the channel. This removal and movement of rocks downstream by the river is known as erosion.
- lateral erosion; widens the channel
-vertical erosion; deeps the channel

4 erosional processes
(a) hydraulic action
the force of the running water hits against the river banks (sides) and bed and surges into lines of weakness such as joints and cracks. the sheer force breaks and loosens rocks and sweeps the rock fragments away.
an example of hydraulic action is the formation of plunge pools at the foot of the waterfall.

(b) abrasion/corrasion
the load of the river grinds against the bed and sides of the channel, loosening and removing rock fragments. the process widens the channel through lateral abrasion, and deepens the channel through vertical abrasion.
abrasion is particularly effective during a flood when the river's energy is  at its maximum.

(c) solution/corrosion
the solvent action of the river water dissolves soluble materials (e.g. limestone) which are then carried away in solution. the carbon dioxide dissolved in the water reacts chemically with calcium carbonate, causing it to change to a soluble calcium hydrogen carbonate.

(d) attrition
the rocks fragments being carried away by the river (load of the river) constantly collide with one another. through this process, rough edges are smoothed out and larger rocks are broken into smaler fragements. the load eventually becomes smaller, smoother and more rounded.

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1. Waterfalls & Plunge Pools
2. Rapids
3. Gorges
4. Potholes

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V-shaped valley
deep, narrow, steep sided

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Transportation:
When a river has sufficient energy, materials will be carried/transported downstream.

1. Traction
- Larger rocks like bigger pebbles and boulders
- Slide along river bed
- Move only if speed of river's great enough to move them
- Some are so heavy they can only be rolled along during heavy flooding

2. Saltation
- When river energy increases
- Coarse sand and other small rock fragments like gravel
- Lifted up briefly then dropped on river bed so they bounce along in a series of "jumps"/"hops" along the river bed

3. Suspension
- Fine particles like fine sand, silt and clay
- Lifted off bed and carried away in water as suspension load
- Suspension loads forms largest part of river load
- Suspension load also responsible for giving water a murky appearance

4. Solution
- Soluble materials in rocks like salts/calcium/sodium dissolve in water and are carried away in solution
- Dissolved materials can't be seen
- Solution can occur even when speed of river and volume of water are low

Deposition:
A river deposits its load when the volume and speed of water decreases and is carrying a greater load than it can transport.

Heaver materials always deposited first then lighter materials because there is not enough energy to carry the heavy materials (require more energy)

Volume can decrease when:
- little/no rain falls (E.g. dry season)
- river flows across arid area where there's a high rate of evaporation
- river flows across permeable rocks > water sinks in
- flood water brought by storm's drained away

Speed can decrease when:
- sudden change of gradient (E.g. river leaving mountain & entering flat lowland)
- river flows into another body of water like lake/calm sea
- increase in wetted perimeter > more friction (E.g. river overflowing banks and entering flood plain)
- water flowing in shallow section of river (E.g. convex bank of meander) > encounters friction
- obstruction (E.g. mounds of deposits/rock outcrops) make channel rougher > increase friction

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the valley is:
-deep, narrow and steep sided.
The steep slopes come down to the side of the river channel like a V shape

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- Small, narrow, shallow
- Rough bed
- Large angular boulders and stones of different sizes
- Few tributaries bring water to the river --> low river volume

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-Meanders
-River cliff and slip off slopes