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- Permeability of rock (Infiltration)
- Presence of vegetation (Infiltration)
- Temperature
- Rainfall (Amount of water entering the river)
- Size of drainage basin (Amount of water entering the river)

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- Gradient
- Channel roughness (friction)
- Wetted perimeter (friction) ((Shape of river channel)
- Shape of river course

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Using natural resources to minimise the damages caused by flooding.

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If river levels rise significantly it is also possible for relief channels to flood as well. Flood relief channels pose a threat to areas near the confluence between the channel and whichever river it flows into as the discharge here will be increased and so too will the risk of flooding. In addition, the path that these channels take are around areas not usually used to flooding. If the flood relief channel was o fail for some reason, this could cause widespread damage.

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This refers to artificial channels that a river can flow into when its discharges rises. These Chanels move water around an area at risk of flooding and send it wither back into the river (but further downstream) or into another river. Flood relief channels generally have floodgates on them that can be used to control the volume of water.
The relief channels can accommodate the surplus water from the river so that it won't overflow its banks.
For example, the Jubilee River in the United Kingdom is part of The Maidenhead, Windsor and Eton Flood Alleviation Scheme built in 2001. It acts as a flood relief channel for the River Thames, allowing water levels to be controlled ad diverted from the Thames during times of high flows, Its use in 2003 protected more then 1000 properties from flooding in the area.
However, it can be hard to find land to built relief channels as they are expensive. For example, in United Kingdom, the Oxford Flood Alleviation Scheme is due to receive 57.7 million Euros in government funding over the life maintenance of the project.

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For example, along the River Conwy in North Wales, embankments 3 metes in height have been built in the area of Llanwrst. They were built in 2001 and newer embankments were installed in 2010. These embankments have minimised flooding in the area effectively by preventing the river to overflow its banks.
However, materials that are used in embankments are not permanent. Flood water may break through at weaker sections of the embankments. Flooding can be extensive because of the extensive low-lying lands. Embankments involve high costs of maintenance as regular checks, maintenance and repairs have to be carried out.

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This refers to the method of constructing embankments or levees on the sides of a river channel so as to increase the height of the river banks to contain flood waters. Earth, sand, stones, shingles and clay sourced from the surrounding areas are a few of the materials used to build these embankments.
The purpose of embanking is to create a river channel with a greater capacity to hold river water, especially in times of flooding. Embanking is especially useful at the lower course of a river where the land is low and flat and where floods are frequent due to the river's proximity to a delta.

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Re-sectioning is usually in situations where the lower course of a river is located in an urban area and is prone to frequent flooding. An engaged river channel hals to quickly channel flood waters away from residential areas.
River Erewash at Stapleford, Derby, England is an example of a river that has been re-setioned, The smooth concrete walls of the channel are effective in increasing river velocity.
However, after re-sectioning is done, the river velocity is reduced due to a larger wetted perimeter. This increases deposition along the river bed which will decrease channel size over time. A lot of resources (funds & manpower) are required for regular maintenance such as dredging and bank reinforcement. Another limitation is the destruction of bed and bank habitats.

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This method enlarges the river channel by either widening or deepening it so as to increase its cross-sectional area. A mechanical dredger or an excavator is used to widen and deepen the river channel and to smoothen and flatten the rough river bed and channel sides so as to reduce friction and increase river velocity. Concrete could be used to line the sides and the bed of the river channel to make them more permanent. An enlarged river channel will be able to hold more river water such as during times of flooding.

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However, there were several unintended negative impacts. 160 km^2 of floodplain below Lake Kissimmee dried out leading to other ecological issues such as the loss of 12,000 - 14000 hectares of wetlands, a reduction in wading bird and water fowl usage and a continuing decline in game fish populations.

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However, re-alignment flattens and smoothens river bed and channel side. This reduces friction and increases river velocity leading to increased erosion or river channel. This occurs because of the increase in the river's ability to transport load. Without much river load to transport, the river tends to have greater erosive power to erode its channel along the upstream part of the straightened river course.
High cost is involved as highly mechanised tools are needed, e.g. mechanical dredger (cranelike machine). A large amount of concrete is also used to line the channel sides. Re-alignment's effectiveness is limited only to smaller floods. It cannot prevent large floods.
For example, Kissimmee River and its adjoining floodplain were channelised and transformed into a 90km, 10m deep drainage canal to provide flood protection for land adjacent to the river, shortening the 166km distance fro Lake Kissimmee to Lake Okeechobee to just 90km.

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This refers to the method of straightening the river channel along a part of a river course. It is normally done to a bend in river, such as a meander. The meander could be cut off by building a concrete wall across the downstream end of a mender. The concrete wall increases the gradient of the river which helps to increase the river velocity.
A straightened river channel is able to quickly transport flood waters out of a flood prone area so as to reduce the damage the flood may cause to the area.
E.g. Mississippi River is shortened by about 240 km after re-alignment by cutting off one of its meanders though its neck. The straightened section allows water to flow away from the area quickly and wash away sediments which have accumulated on the river bed. This deepens the channel allowing it to hold more water, reducing flood

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Physically building structures to try and prevent flooding (e.g. walls). Hard engineering usually involves the use of concrete, steel, rock and wood.

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This generally refers to the various engineering methods used by people to modify river channels so as to manage the flow of river water an alleviate problems such as flooding and erosion.

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The volume of the river is in between the upper and lower course.

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-- deep, narrow, steep-sided, V-shaped

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1. river flows over alternating bands of rocks of different resistance, more and less resistant

2. less resistant rock erodes at a faster rate and a small depression is formed

3. difference in rates of erosion between the two types of rocks causes a change in gradient of the river. A waterfall is formed

4. sudden drop in height causes water to plunge down vertically. This force erodes the base of the waterfall deepening the depression.

5. The rock debris swirl about in the base of the waterfall due to the turbulent water, further deepening the depression and forming a plunge poo

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☆.｡.:* River cliff and slip off slopes  .｡.:*☆

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☆.｡.:* River cliff and slip off slopes  .｡.:*☆

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The relationship between velocity and particle size

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The relationship between velocity and particle size

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For grain size 0.5mm and above in diameter, the larger the particle, the higher the velocity required to erode them.

For grain size smaller the 0.5mm in diameter, the smaller the particle, the higher velocity needed.

After erosion, particles can be transported at any velocity until its low enough for deposition to occur.

Large particles are deposited shortly after erosion as a small drop in velocity is enough for it to be deposited.

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Arcuate delta
- triangular/fan-shaped
- has many distributaries
- alluvial deposits are evenly spread out
e.g. Nile Delta, Egypt

Bird's Foot delta
- distributaries extend far into the water
- discharge is high
- load is enormous
e.g. Mississippi Delta, USA

Estuarine delta
- load deposited in a long, narrow & submerged estuary (where the tide meets the river)
- does not grow beyond the general coastline because waves & currents wash away the sediments deposited outside the estuary.
e.g. Seine Delta, France

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The river begins to deposit its load when the volume and speed of the water decreases and is carrying a greater load than it can transport.

Volume of river decreases when:
- little or no rain falls
- the river flows across an area with a high rate of evaporation
- the river flows across permeable rocks to allow water to sink in
- flood water brought by storm has drained away
Speed of river decreases when:
- sudden change in gradient
- river flows into another body of water
- increase in wetted perimeter which results in more friction
- water flowing in shallow section of the river
- obstructions make the channel rougher and increases friction

When a river loses energy, heavier material is the first to be deposited. Gravel, sand and silt are transported further before they are deposited as they are smaller in size.

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more rough > lower speed
more smooth > higher speed

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Area in the channel that is in contact with the river

Larger wetted perimeter = more friction, less speed

Smaller wetted perimeter = less friction, more speed

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-- shape is small, narrow and usually shallow
-- bed is rough --> presence of large angular boulder and stone  of different sizes
-- weathering and erosion = bed load --> increases wetted perimeter = decreases speed of flow
-- volume is small, few tributaries to bring water

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-Natural embankments found along the banks of the river
-Made up of coarser alluvial deposits than the flood plain

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- created as a result of erosion/ deposition
- accumulation of river deposits ( suggests they are predominantly depositional features )
- flat areas of land on either side of the river
- composed of alluvium
- overtime: floodplain becomes wider --> depth of sediment accretions increase

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-- steep, V-shaped valley
-- narrow / shallow channel
-- high bedload

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Continuous Erosion

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1.
when river enters the sea, speed is checked & load is deposited (seawater causes clay to flocculate).

2.
river continues to deposit load @ mouth. materials accumulate and extends outward from mouth.

3.
platform of alluvium is built up & rises.

4. more materials accumulate & rise above the water, forming a DELTA. river water overflows into different channels (distributaries). vegetation grows on the alluvium & stabilise the delta.

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- high permeability (loose soil) ( = high infiltration = less surface runoff) = lower volume in river

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dry climate > volume remains low year round

hot and wet climate > volume remains high all year round

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higher rainfall - greater volume
less rainfall - less volume

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-Depression in the river bed
-Varies in size and ranges from a few centimetres to as large as metres in diameter.

-Formed by river abrasion
Abrasion=when the load river grinds against the bed and sides of the channel, loosening and removing rocks fragments. Widens the channel through lateral abrasion, and deepens the channel through vertical abrasion.

-Abrasive action is especially effective in flood condition.
- pebbles and cobbles that are trapped in slight holes in the river bed are swirled about in currents and turbulence of fast flowing water.

^they drill the holes, enlarging and deepening them.

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The higher velocity on the concave bank causes the current from the bank to descend undercutting and eroding the concave bank

Lower velocity on the convex bank results in the deposition and build up of eroded materials on the convex bank

Undercutting of the concave bank results i the slumping of materials forming a steep cliff on the concave bank

Continuous deposition and build up of eroded materials forms a gentle sloping slip off slope

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- sufficient load carried by river
- absence/few lakes along the river -> could trap load
- gentle offshore gradient & shallow water -> easier buildup of sediments
- quiet coastal waters & absence of strong current
- climate favouring growth of fast-growing vegetation -> stabilise materials

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Vertical erosion is further increased by the rough nature of the channel
= increases the water's turbulence and its ability to erode

The turbulence of the water = causes the bed load to swirl in whirlpools, abrading the bed and causes portholes to form.

The river mainly transports large pieces of angular rock and does so by traction because it does not have enough kinetic energy to move the load in another way,

This increases erosion of the bed by corrosion as a result of the load being dragged along the bed of the river.

Erosion and transportation only takes place in large quantities in the upper course when the river's volume is high after periods of heavy precipitation.

When the river's discharge falls the river stops transporting the large boulders its transporting and deposits them.

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River has less gravitational potential energy and more kinetic energy so erosion shifts from vertical to lateral erosion.

abrasion is the main erosive process as large particles are transported by saltation

average load size has decreased so more load is transported in suspension

river can flood and in doing so, it deposits gravel and sand sized particles onto its flood plain

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- more vegetation ( = more infiltration = decreased surface runoff) = lower volume in river

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Horse shoes or crescent-shaped lake

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river starts to meander
channel is wider and deeper

cross section is asymmetrical in shape when a steep river cliff develops on the concave bank (outer bank) of the meander and a gentler slip off slope develops on the convex (inner bank) of the meander

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widest and deepest -> holds largest volume of water & load

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- shape
- size
- volume
- loads

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Wide and Shallow

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In the upper course:
- The river has a lot of gravitational potential energy so it has a lot of energy to erode vertically '

- The bed of the river is eroded greatly while the banks are not eroded as much

- The vertical erosion of channel: gives valley the characteristic of a DEEP, NARROW, STEEP- SIDED V SHAPE.

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- bigger basin = higher volume in river
- smaller basin = lower volume in river

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results from erosional/depositional processes
1. bars of sediment on river bed causes water to swing side to side
2. causes undercutting on one side; material is deposited on the other side
3. continued erosion along the outer bank creates a river cliff. a slip off slope  forms on the inner bank.
4. helicoidal flow allows meanders to perpetuate

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Definition:
A gorge is a deep narrow valley with steep, almost vertical sides.

A gorge will develop when a waterfall retreats upstream

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- Oxbow lake
- Floodplains
- Levees
- Deltas

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1. Hydraulic Action
- The force of the running water hitting against the river banks which breaks and loosens rocks and sweeps rock fragments away
2. Abrasion/Corrasion
- The river load grinds against the bed and sides of the channel, loosening and removing rock fragments, resulting in the channel becoming deeper and wider
3. Attrition
- The river load constantly collides with one another, becoming smaller, smoother and more rounded
4. Solution/Corrosion
- The river water dissolves soluble materials, through the carbon dioxide that dissolved in the water which reacts chemically with calcium carbonate, causing it to change to a soluble hydrogen carbonate

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Definition:
A waterfall is a sudden and rapid vertical fall of water along the course of the river

Definition:
A plunge pool is a deep basin excavated at the foot of a waterfall by the action of falling water

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wider V-shape + floor

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1. Traction
Large rocks (Bigger pebbles and boulders) slide and roll along the river bed.
2. Saltation
Coarse sand and small rock fragments get lifted, then get dropped, making them bounce along the river bed.
3. Suspension
Form the largest part of river load. Fine particles (fine sand, silt, clay) are lifted off the bed and carried away in water as suspension load.
4. Solution
Soluable minerals in rocks (salts, calcium and sodium) dissolve in water and are carried away in solution. This cannot be seen and can occur at any speed of river and volume of water.

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steeper - faster
gentler - slower
steep at source, gentler towards mouth

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1. Waterfall and plunge pools
2. Gorges
3. Rapids
4. Potholes