Rivers Flashcards
What is a watershed of a river?
Marks the edge oof a drainage basin ( highest point of land )
What is a source of a river?
Starting point of a river
What is the confluence of a river?
A point where a smaller river ( like a tributary ) join the main river
What is a tributary of a river?
A small stream which joins the main channel
What is the mouth of a river?
A point which the river enters the sea
What is meant by the long profile of a river?
Long profile of a river is the change in gradient ( steepness ) as the river goes from source to mouth. It starts off steep from the top and becomes more flatter at the lower course ( concave profile )
How and why does the depth of a channel change from source to mouth of a river ?
Width and depth increases. Starts of with vertical erosion then followed by lateral erosion as the river moves along the coast.
How does velocity change with distance downstream
Speed of flow increases with distance downstream. This is because there’s less friction due to less contact with between the river bed and banks
How does the gradient change with distance downstream?
It will decrease as the river flows downstream as it passes from an upland area down to a lowland area where it enters the sea.
How does discharge change with distance downstream?
As the river goes downstream it is fed by more tributaries and therefore discharge increases.
What features are found in the upper course of a river?
V shaped valleys
Waterfalls
Gorges
What features are found in the middle course of a river?
Meanders
Ox bow lakes
What features are found in the lower course of a river?
Levees
Floodplains
Which river features are examples of deposition and erosion processes?
Floodplains
Meanders
Ox bow lakes
Formation of a waterfall
-This is when soft rock is eroded quicker than hard rock, but hard rock is gradually undercut via hydraulic action and abrasion
-(the force of falling water creates a plunge pool)
-Eventually the cap rock is left unsupported due to the undercutting and collapses
-(fallen rock enlarges the plunge pool via abrasion)
-the process repeats itself an da gorge is formed as the waterfall retreats upstream
Formation of a meander
- the swing of the flow of the water within the channel results in water being flung to the outer bank causes faster flow and greater erosion on the outer bank
- this creates a river cliff due to undercutting by lateral erosion
-on the inner bend : slow flowing due to shallower, low energy zone and deposition occurs due to low velocity, creating a slip off slope
Formation of a floodplain and levee
- when a river floods, water spreads over the surface and there is increased frictional drag resulting in deposition
-Subsequent periods of flooding results in layers of material building up a fertile floodplain
-when a river bursts its bank the largest material is deposited closest to the edge of the river and finer material travels further resulting in levees
Formation of ox bow lake
-Meanders necks narrow due to erosion on the outer beds
-Eventually the 2 outer bends meet and the river cuts through the neck of the meander ( this is because the water will now take a shorter route rather than flowing around )
-Deposition gradually seals off the old meander bend, forming a straight river
-Old meander bend has been left isolated from the main channel and over time this feature may fill up with sediment.
What is the difference in velocity between the inner bend and outer bend of a meander?
On the outer bend: it will be faster because its deeper and less frictional drag resulting in erosion.
On the inner bend: it will be slower because there’s more frictional drag and its shallower resulting in deposition.
What are the typical characteristics of a waterfall?
-deep plunge pool
-Steep sided gorge
What are the main changes in a river channel from the upper to the lower course?
-Upper course: narrow channel, a few meters wide and very shallow
Middle course: channel becomes wider and will often be over a meter deep
-Lower course: river channel becomes wide and deep
Give 3 examples of river management techniques that are hard engineering.
- Dams and reservoirs
- Channel straightening
- Flood relief channels
- Embankments
What is a dam and reservoir and how do they help manage rivers?
Dams: large concrete barriers built across rivers to impede flow.
Reservoir: formed behind a dam which enables the flow of a river to be controlled and reduces the risk of flow downstream
What is a hydrograph?
A graph which shows how a rivers discharge changes in response to a precipitation event.
Define thee following:
- Lag time
- Rising limb
- Peak discharge
- Base flow
- Lag time: the difference between peak rainfall and peak discharge
- Rising limb: this shows how quickly the discharge rises after a rain storm
- Peak discharge: the highest recorded discharge following a rainfall event
- Base flow: normal flow of a river when its water level is sustained by groundwater flow
Give 3 ways in which change rural land-use can increase flood risk
- Forestry: chopping down trees reduces interception and less water is taken up from the soil
- Farming: soil is bare in the winter so nothing to intercept the rainfall
- Increase in greenfield sites are being sold off to developers for housing or other human land-use ( increasing impermeable surfaces )
Define the following terms:
- Soil moisture
- Evaporation
- Water table
- Soil moisture - water held in soil
- Evaporation - water lost from the ground ( liquid to vapour )
- Water table: upper level of saturated zone in the soil
How does channel straightening reduce flood risk?
It provides a more efficient channel allowing water to pass through quicker reducing the likelihood of a flood. ( flow is slower in meandering channels due to friction )
Formation of an interlocking spur
The river cuts down into the valley. If there are areas of hard rock which are harder to erode, the river will bend around it.
