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Define: River discharge
Volume of water passing through a cross-section of a river during any given time period
Define: Lag time
The period of time between the end of rainfall and the peak discharge
A substance that allows water to pass through it
A substance that doesn't allow water to pass through it
- a material that has tiny pores through which water or air may pass
- e.g. clay
- a material which doesn't allow liquid or air to pass through it
- e.g. granite
Describes materials that have cracks, joints or bedding planes that allows water through
Define: antecedent flow rate
the level of water in the channel before the precipitation event
Define: river regime
the changing pattern of river discharge over a period of time, usually a year
Define: base level
the lowest point to which a river or stream can flow
Define: mass movement
- the shifting of debris under the influence of gravity, the extent of which varies depending on the steepness of the slope and the amount of water in material.
- more water = faster movement
- e.g. landslides
Rocks and boulders colliding with one another as they move down the river and are broken into smaller pieces
Define: hydraulic action
- The sheer power of the waves which dislodges loose particles from the river bed or banks.
- Most effective during high water flow
Rocks carried by the river hit its beds and banks, wearing them away as well as dislodging rock particles, which adds to the load in the river
- Chemicals in water break down debris and particles are carried among with the water flow
- A continual process that is most active on rocks that contain carbonates, such as limestone
The decomposition of rocks 'in situ' on the earth's surface
Define: biological weathering
The breakdown of rocks due to living organisms
Define: chemical weathering
The breakdown of rocks due to chemical reactions
Define: acid rain
precipitation that has become acidic due to atmospheric pollution
Define: freeze thaw
water freezing in cracks in rocks which, when repeated, puts pressure on rocks until they eventually break
Define: river long profile
An illustration that depicts the changes in altitude over the course of the river from its source along the entire length of its channel to the river mouth
Define: knick points
Marked breaks or changes in the river long profile, such as waterfalls or rapids
The maximum diameter of the particle the river can carry for a given velocity
Total volume of material the river can catty at any one given time
Define: interlocking spurs
Ridges of more resistant rock around which a river is forced to wind as it passes downstream in the upper course
What are the main characteristics of the upper course of a river?
- Steep V shaped valley
- Narrow and shallow channel
- High bedload
What are the landforms found in the upper course? (7)
- V-shaped valleys
- interlocking spurs
- braided river
What are the characteristics of the middle course of a river?
- Open/gentle sloping valley with floodplain
- Wider/deeper channel
- More suspended sediment
What are the landforms found in the middle course of a river? (5)
- River cliffs
- slip off slopes
- Pools and riffles
- ox-bow lakes
What are the characteristics of the lower course of the river?
- Open/gentle sloping valley with floodplain
- Flat and wide floodplain
- Wide, open valley
- Very wide and very deep channel
What landforms/features are found in the lower course of the river?
Define: v- shaped valley
A valley which resembles a 'v' in cross section. These valleys have steep sloping sides and narrow bottoms
Define: interlocking spur
Ridges of more resistant rock around which the river is forced to wind as it passes downstream in the upper course
What is slumping?
A slower form of mass movement which can be found in the upper course of a river on the steep valley sides
What are terracettes and how are they formed?
Terracettes are small raised areas on the valley side which are formed by soil creep
Does the upper course have a small or large bedload and why?
Large bedload because of upstream erosion and mass movement from valley sides
How are v-shaped valleys formed? (4 steps)
1. Vertical erosion (in the form of abrasion, hydraulic action and solution) in the river channel forms steep valley sides
2. Over time, the valley sides are weakened by weathering and further vertical erosion at the base of the valley
3. Mass movement of materials occur down the valley sides, creating distinctive v shape
4. This material is then transported away by the river during peak discharge and high energy
How are interlocking spurs formed?
When the river flows through the valley it is forced to swing from side to side around more resistant rock outcrops (which are called spurs). As there is little energy for lateral erosion the river continues to erode vertically, flowing between spurs of higher land which creates interlocking spurs
Shallow, slow moving mini waterfalls
How are rapids formed?
Rapids form where protruding bands of more resistant strata create steps over which rapids fall - the river bed is ungraded.
How much of the river's energy is lost when it travels over rapids?
Explain the formation of a waterfall
Waterfalls occur when a band of more resistant rock (e.g. granite) overlies a band of less resistant rock (e.g. sandstone)
- As the river passes over the resistant rock, the soft rock below is eroded underneath. This leaves the hard rock elevated above the stream below.
- The drop gets steeper as the river vertically erodes the soft rock through abrasion and hydraulic action. A plunge pool forms at the base of the waterfall
Eventually the hard cap rock collapses, as it is unsupported. The rock falls into the plunge pool and will continue to enlarge it due to abrasion,
A steep sided gorge is left behind as the processes of undercutting and collapse continue
Name an example of a waterfall
High Force, River Tees, England
Semi-circular depressions sometimes formed above the river channel caused by abrasion during high discharge events
Under what circumstances may two or more potholes become one?
If the competence is sufficient to be carried during high discharge events, uneven abrasion and vertical erosion
What is pothole drilling?
River load getting trapped in cracks in the river which is then swirled around by eddies in turbulent flowing water. this leads to abrasion of the crack - known as drilling
Where can braided rivers be found?
- In semi-arid or mountainous areas where there are large fluctuations in discharge and high volumes of easily transported bedload (e.g. sand)
- e.g. the swiss alps
How does material end up in braided rivers?
As a result of freeze thaw (from recent glaciation) and mass movement
What is the bed load like in the upper course?
- Large and angular
- Semi rounded due to attrition+abrasion
What does the long profile of the middle course look like?
Increasingly sinuous and graded. Lateral erosion takes over from vertical erosion as the gradient decreases
How are riffles and pools formed?
Alternating bars of sediment in the river channel cause the river to weave around them, which produces shallow, faster flowing riffles and deeper, slower flowing pools.
What is the thalweg?
The zone of maximum velocity