River Landscapes in the UK Flashcards
All 63 cards in this deck
What is the long profile of a river?
A side view along the river's course showing how the height (gradient) of the river channel changes from source to mouth.
What is the cross profile of a river?
A cross-section taken across the river valley and channel at one point along its course.
Give one way a river valley may change as it goes downstream.
The valley gradient becomes less steep (also: the valley becomes wider/more open, or a flood plain develops).
True or false? A river channel generally gets wider as it flows downstream.
True. The river increases in width downstream from the source.
What is hydraulic action?
The force of moving water (and air compressed into cracks) breaking material away from the bed and banks.
What is abrasion in a river?
Sediment carried by the river scrapes against the bed and banks, wearing them away.
What is attrition?
Stones carried by the river collide with each other and break down, becoming smaller and rounder.
What is solution (corrosion) as a river erosion process?
Slightly acidic river water dissolves soluble rocks such as limestone and chalk.
What is the difference between vertical and lateral erosion?
Vertical erosion cuts downwards, deepening the channel and valley; lateral erosion cuts sideways, widening them.
What is traction as a transport process?
Large, heavy pebbles are rolled along the river bed.
What is saltation as a transport process?
Pebbles are bounced along the river bed.
What is suspension as a transport process?
Lighter sediment is carried (suspended) within the water.
What is solution as a transport process?
Material is carried as dissolved minerals within the water.
Why do rivers deposit sediment?
Because the river loses energy (velocity) and can no longer transport its load, e.g. in shallow water, on the inside of a bend, or at the mouth.
Give one reason the median size of sediment decreases downstream from the source.
Attrition between particles breaks the load down into smaller pieces.
What are interlocking spurs?
Ridges of higher land projecting into the valley from alternate sides, which the river winds around in its upper course.
What arrangement of rock types is needed for a waterfall to form?
A band of hard (resistant) rock lying over softer, less resistant rock.
What is a plunge pool?
A deep pool at the foot of a waterfall, eroded by hydraulic action and abrasion from the falling water and rocks.
What are the steps in the formation of a gorge below a waterfall?
e.g. a waterfall where hard rock lies over soft rock- The soft rock beneath is eroded, undercutting the hard rock and forming an overhang.
- The unsupported hard rock collapses into the plunge pool.
- Repeated collapse makes the waterfall retreat upstream, leaving a narrow, steep-sided gorge.
What is a meander?
A winding curve or bend in a river.
What happens on the outside bend of a meander?
Water flows fastest in the deeper channel, so lateral erosion undercuts the bank and forms a steep river cliff.
What happens on the inside bend of a meander?
Flow is slower and shallower with more friction, so material is deposited, forming a slip-off slope.
What are the steps in the formation of an ox-bow lake?
e.g. a large meander on a flood plain- Lateral erosion on opposite sides narrows the neck of the meander.
- In a flood the river breaks through the neck and takes the shorter, straighter route.
- Deposition cuts off the old meander, leaving a curved ox-bow lake.
What is a levée?
A long, raised ridge or embankment of sediment along the river banks, higher than the flood plain and steeper on the channel side.
When a river floods, which material is deposited closest to the channel?
The largest, heaviest material (sand and gravel); finer silt and mud is carried further across the flood plain.
What is a flood plain?
The wide, flat area of land either side of a river that is covered in water when the river floods, built up by deposited sediment.
What is an estuary?
The wide, shallow river mouth where the river meets the sea, with mudflats and salt marshes formed from deposited silt and mud.
Which landforms would you expect to find in the upper course of a UK river valley?
A steep-sided V-shaped valley with interlocking spurs, waterfalls and gorges.
Give three landforms you would expect to find in the lower course of a UK river valley.
Any three of: meanders, ox-bow lakes, levées, a wide flood plain, an estuary.
What effect does impermeable rock or soil (e.g. granite or clay) have on flood risk?
It increases flood risk: water cannot pass through, so surface runoff increases and reaches the river quickly.
What effect does steep relief have on flood risk?
It increases flood risk: steep slopes give greater, faster overland flow and a shorter lag time, with less time for infiltration.
Why does heavy rainfall cause a greater flood risk than slow, light rain?
Heavy rain rapidly saturates the upper soil, so excess water reaches the river quickly as surface runoff (short lag time); light rain can infiltrate.
Why does urban land use increase flood risk?
Concrete and tarmac are impermeable, so surface runoff is high and drains carry water to the river quickly.
True or false? Planting vegetation in a drainage basin increases flood risk.
False. Vegetation intercepts rainfall and encourages infiltration, lengthening lag time and reducing flood risk.
What is a storm (flood) hydrograph?
A graph showing rainfall and river discharge at a point on a river over the period of time following a storm.
What is river discharge, and in what units is it measured?
The volume of water passing a point in the river per second, measured in cumecs (cubic metres per second).
What is lag time on a hydrograph?
The time between peak rainfall and peak discharge.
True or false? A long lag time on a hydrograph means a higher risk of flooding.
False. A short lag time with a steep rising limb and high peak discharge (a flashy hydrograph) means a higher flood risk.
What is hard engineering in river management?
Using man-made structures to prevent or control natural processes; usually very expensive but effective at preventing flooding.
What is soft engineering in river management?
Working with nature and natural river processes to reduce flood risk; low cost, low maintenance and little environmental impact.
How do dams and reservoirs reduce flood risk?
A dam traps water in a reservoir, storing it during heavy rain and releasing it in a controlled way; the water also supplies drinking water and HEP.
Give one cost of dams and reservoirs.
Very expensive, and the reservoir floods land and displaces people; trapped sediment and blocked fish migration damage habitats.
What is channel straightening, and how does it reduce flood risk?
Removing meanders so the river is shorter and faster, moving water out of the area more quickly; it also improves navigation.
Give one cost of channel straightening.
It destroys habitats and changes the river's ecosystem; concrete linings are unattractive and faster flow can increase flooding downstream.
What are embankments as a flood management strategy?
Raised banks built along the river so it can hold more water and floods less often, protecting buildings on the flood plain.
Give one cost of embankments.
High maintenance costs and reduced access to the river; concrete or gabion embankments break up habitats and look unattractive.
What is a flood relief channel?
An artificial channel that takes excess water around or away from a settlement when river discharge is high; it can also create new aquatic habitats.
What are flood warnings and preparation?
Monitoring rivers and warning people so they can prepare and act; people may not respond, especially after false alarms.
What is flood plain zoning?
Restricting building and development on the flood plain so land at highest risk is used only for low-value uses such as grazing, wetlands or recreation.
What is river restoration?
Returning a hard-engineered river to its natural channel, e.g. removing straightening or levées, reducing discharge downstream and increasing biodiversity.
True or false? Solution is both a process of erosion and a process of transport in a river.
True. Solution erodes soluble rock such as limestone, and also carries dissolved minerals within the water.
True or false? An ox-bow lake stays joined to the river at one end.
False. Deposition cuts the old meander off completely, leaving a lake separated from the main river.
Why can a long period of steady rain cause flooding even if the rain is not heavy?
The rain gradually saturates the ground, so once the soil is full, later rain cannot soak in. It flows over the surface into the river instead, raising discharge.
What is peak discharge on a hydrograph?
The highest discharge the river reaches after the storm, shown by the top of the discharge line.
What do the rising limb and the falling limb of a hydrograph show?
Rising limb: discharge increasing as rainwater reaches the channel. Falling limb: discharge decreasing back towards normal after the peak.
Where along a river does vertical erosion dominate, and where does lateral erosion dominate?
Vertical erosion dominates in the upper course, cutting a steep V-shaped valley. Lateral erosion dominates in the middle and lower course, widening the valley.
True or false? A river channel becomes shallower as it flows downstream.
False. The channel gets deeper as well as wider downstream, because it carries a larger volume of water.
How do meanders help to widen a flood plain?
Meanders migrate across the valley, and lateral erosion on their outer bends cuts away the valley sides, so the flat valley floor gets wider.
How do mudflats form in an estuary?
As the tide comes in, river water is held back and slows, so it deposits silt. Over time this builds up mudflats that are uncovered at low tide.
Give one cost of planting trees to reduce flood risk.
The land can no longer be used for farming (also: it takes years before young trees have much effect).
Give one cost of a flood relief channel.
Where the channel rejoins the river, discharge rises, which can increase flood risk downstream (also: it is expensive to build).
Give one cost of flood plain zoning.
It does not protect buildings already on the flood plain (also: it limits where a settlement can expand).
Give one cost of river restoration.
Letting the river flood its natural land can increase flood risk locally, for example on nearby farmland.