River Landscapes in the UK Flashcards
What is a river’s path called?
What does the long profile of a river show?
What does the cross profile of a river show?
Course
How the gradient changes
The cross-section of the river
Describe the upper course of a river
Steep, v-shaped valley, narrow, shallow channel
Describe the middle course of a river
medium gradient, gently-sloping valley, wider, deeper channel
Describe the lower course of a river
gentle gradient, almost flat valley, very wide, deep channel
Name and define the four erosion processes
Hydraulic action - force of the water colliding with rocks
Abrasion - rocks picked up by the river scrape against the channel
Attrition - rocks picked up by the river bang into each other, becoming smaller and rounder
Solution - river water dissolves some types of rock
Name and define the four transportation processes
Traction - large particles (boulders) are pushed along the river bed
Suspension - small particles are carried by the water
Saltation - pebble-sized particles ‘bounce’ along the river bed
Solution - soluble materials dissolve and are carried along
Where in the river course do waterfalls form?
What process causes waterfalls to form?
What type of rock formation is needed for a waterfall to form?
Upper course
Erosion
Hard rock on top of soft rock
How is a waterfall formed?
River flows from hard rock onto soft rock
Soft rock is eroded quickly - creates a drop
Water falls into a turbulent plunge pool
Abrasion/ hydraulic action erodes the soft rock underneath, creates an overhang of hard rock
The hard rock is undercut, making it collapse
The waterfall retreats - the process repeats
How is a gorge formed?
When a waterfall retreats, it leaves behind a narrow, steep-sided valley (a gorge)
Where in the river course are interlocking spurs found?
What process causes interlocking spurs to form?
Upper course
Erosion
How are interlocking spurs formed?
In the upper course, erosion is vertically downwards
River lacks power to erode laterally
So it has to wind against the hillsides in its path
This makes a winding river in between interlocking hills
Where in the river course are meanders found?
What process causes meanders to form?
What is a meander?
Middle course
(lateral) Erosion and deposition
A bend in a river
How are meanders formed?
Current is faster on the outside of the bend (river channel is deeper = less friction) = more erosion
Helicoidal flow (corkscrew motion) moves material from the outside of one bend to the inside of another
Current is slower on the inside (river channel is shallower = more friction) = more deposition
Compare the inside of a meander bend to the outside
Inside:
deposition, slower flow, shallow, river beach/ slip-off slope
Outside:
erosion, fastest flow, deeper, river cliff (caused by erosion from helicoidal flow)
How is an ox-bow lake formed?
Meanders get larger over time - erosion causes the outside bends of two meanders to get closer
Eventually, the river breaks through the neck of the meander
River flows through the shortest course
Deposition cuts off the meander = ox-bow lake
What is a flood-plain?
Where in the river course are flood plains found?
What process causes flood plains to form?
The wide valley floor on either side of a river that occasionally floods
Lower course
Deposition
How are flood-plains built up over time?
When rivers flood, the water slows down, loses energy and deposits the material it was transporting
The deposition that happens on slip-off slopes of meanders also build it up
Where in the river course are levees found?
What process causes levees to form?
What are levees?
Lower course
Deposition
Natural embankments (raised banks) on the edges of a river channel
Where are estuaries found?
What is the land like in an estuary?
What is the water like in an estuary?
At river mouths (lower course)
Close to sea level, rive valley is at its widest
Tidal
How are estuaries / mudflats formed?
When water floods the banks, it carries silt/sand onto the valley floor
When the tide is highest, it has little energy, deposits sediment
Over time, mud builds up, making mudflats
Mudflats are exposed at low tide
Where is the River Tees located?
Where is its source?
Where is its mouth?
North east England
Pennines
North Sea at Middlesborough
What is the land use in the upper course of the Tees?
What is an example of a landform in the upper course?
What rock types is it made from?
Reservoirs, farming
High Force waterfall
Hard rock = whinstone, soft rock = limestone
What is the land use in the middle course of the Tees?
What is the shape of the valley here?
Farming (95%)
U-shaped
What is the land use in the lower course of the Tees?
a town, nuclear plant, iron/steel works
What is river discharge?
The volume of water flowing per second, measured in cumecs (cubic metres per second)
What does a hydrograph show?
The river discharge after a period of heavy rainfall
On a hydrograph, what is:
Peak discharge
Lag time
Rising limb
Falling limb
Highest discharge on the hydrograph
The delay between peak rainfall and peak discharge
The increase in river discharge
The decrease in river discharge
What factors decrease (flash flood) / increase (slow onset flood) lag time?
Decrease:
- steep gradient of drainage basin
- impermeable rocks (more surface runoff)
- impermeable man made surfaces (“ “)
- saturated soil (“ “)
- small drainage basin
- areas without vegetation (less interception)
- heavy rain (rapid saturation of soil = more surface runoff)
What is hard engineering?
Man-made structures that control the flow of rivers to reduce flooding
What is soft engineering?
Schemes set up using knowledge of a river to reduce the effects of flooding
Explain some examples of hard engineering to reduce flooding.
- Dams / Reservoirs - reservoirs control water flow + HEP produced, BUT expensive, reservoirs flood
- Channel straightening - meanders removed, water leaves area quickly, BUT floods happen downstream
- Embankments - river can hold more water BUT expensive, severe flooding if they break
- Flood relief channels - divert excess water, gates control flow of water BUT increased discharge where relief channel re-joins the river
Explain some examples of soft engineering to reduce flooding.
- Warnings/Preparation - buildings modified, people can prepare BUT no prevention/protection, modifying buildings expensive
- Flood plain zoning - restrictions prevent building here, flood risk reduced BUT urban expansion limited
- Planting trees - increase interception, provides habitats BUT less land for farming
- River restoration - lets the flood-plain flood, little maintenance BUT local flood risk increases
In a named example, what were some flood defences?
Boscastle:
- wider bridge span (more water can flow under)
- lower river bed / widen channel (increase capacity)
- remove dead trees/add trash screens (stops river getting clogged)
