River Landscapes in the UK Flashcards
Erosion: Hydraulic Action
River bank and bed; forces air to become trapped in cracks in rocks, causing rock to break apart
Erosion: Abrasion
River bed and bank, pebbles grind, sand-paper effect
Erosion: Attrition
Rocks hit against each other, breaking apart to become smaller pebbles
Erosion: Solution
Chemical erosion of rocks (eg, limestone and chalk), dissolving them
Transportation: Traction
Large, heavy boulders rolled along river bed, load is larger, (upper course)
Transportation: Saltation
Pebbles bounced along river, (middle course)
Transportation: Suspension
Light sediment is suspended, (lower course)
Transportation: Solution
Dissolved chemicals, soluble rocks (eg, chalk, limestone), (middle, lower course)
Deposition
River loses energy, drops carried material
Factors Leading to Deposition
- Shallow water
- Lower course, current speed changes (estuary)
- Inside bend of a meander (slower current)
Drainage Basin: Area around river drained by river and its tributaries
Water shed — area of high land forming the edge of river basin;
Source — beginning of river;
Mouth — where river meets the sea;
Confluence — point at which two rivers meet;
Tributary — small river or stream that joins larger river;
Channel — where river flows
River Profiles: Long Profile
Line representing the river from its source to its mouth, shows how river changes over its course
Upper Course
Steep gradient; narrow; vertical erosion; hydraulic action; steep valley sides; abrasion and traction; waterfalls, interlocking spurs, gorges, v-shaped valley
Middle Course
Decreasing gradient; wider deeper; energy increases; lateral and vertical erosion; saltation, attrition; higher discharge; meanders, oxbow lakes
Lower Course
Gentle gradient; wider, deeper channel; high energy starts to slow down; lateral, vertical erosion; suspension, solution; levees, deltas, estuaries, floods
Erosional Landforms: Waterfalls and Gorges
Hard rock —> gorge
Soft rock
Plunge pool
1. Soft rock erodes quicker than hard rock —> undercut hard rock —> overhang
2. Overhang collapses, no support
3. Abrasion and hydraulic action erode bottom —> plunge pool
4. Process repeats
5. Waterfall retreats upstream
6. Steep-sided valley left is the gorgeErosional Landforms: Interlocking Spurs
- Vertical erosion
- Hard rocks, hard to erode
- River erodes around interlocking spurs
Erosional & Depositional Landforms: Meanders
Slip-off …. River
slope …. Cliff
Fast current
1. Formed as water moves over shallow areas (riffles) and deep pool sections
2. More energy on outside (corkscrew motion) (hydraulic action, abrasion) —> deeper on outside bend
3. Lateral erosion undercuts outside bend —> river cliff
4. Slower current, less energy on inside bend —> deposit sediment —> slip-off slope
Erosional & Depositional Landforms: Oxbow Lakes
- Hydraulic action, abrasion erode outside bend
- Area between the outside bend of one meander and another decreases —> ‘swan’s neck’
- Channel cuts through meander neck when discharge is high (flood)
- Shorter, straighter, new channel created
- Deposition cuts off original meander, leaving horseshoe—shaped oxbow lake
Depositional Landforms: Floodplains
- Erosion removes interlocking spurs, creating wide, flat area
- Material is carried and deposited —> height of floodplain increases
- Fertile soil —> alluvium (deposited silt from river flood)
- Meanders make it wide
Depositional Landforms: Levees
- During flood, water flows over banks and deposits silts —> largest material deposited first, then smaller material —> higher bank
- In between floods, slow moving river deposits silt in riverbed
- New river level
- With each flood, levees are built up
- Between floods, river bed is built up
- River may flow well above level of floodplain
Depositional Landforms: Estuaries
- During tide rise, river water doesn’t go out to sea, so flow slows down —> silt deposited
- When tide lowers, mudflats exposed, become salt marshes —> important habitat for wildlife
Depositional Landforms: Deltas
Sediment deposited before sea can remove it at the mouth —> forms little areas of land with smaller channels —> tributaries
Causes of Flooding: Prolonged Rainfall
Soil around river becomes saturated —> more surface run-off into river
Causes of Flooding: Heavy Rainfall
Less infiltration of soil —> surface run-off in river
Causes of Flooding: Relief
Steep valley —> more surface run-off into river; water runs too fast for being absorbed and infiltrate soil
Causes of Flooding: Geology
Permeable rocks allow water to infiltrate;
Impermeable rocks —> more surface run-off into river
Causes of Flooding: Vegetation
Trees and plants intercept water, deforestation increases surface run-off and flood risk
Causes of Flooding: Urban Land Use
Tarmac and concrete are impermeable, increasing surface run-off and no infiltration or absorption of water
Hydrograph Info
Peak discharge — maximum volume of water held in channel;
Peak rainfall — maximum amount of rainfall (mm);
Lag time — time taken between peak rainfall and peak discharge;
Rising limb — shows increase in discharge;
Falling limb — shows return of discharge to normal/base flow;
Base flow — normal discharge of river
Factors Influencing Lag Time (Hydrograph)
- Size of drainage basin — large = high p.d., long lag time (v.v.)
- Vegetation — bare = short lag time, high p.d. (v.v.)
- Valley side steepness — steep = short lag time, high p.d. (v.v.)
- Soil type — impermeable = short lag time, high p.d. (v.v.)
Hard Engineering
Involved building artificial structures which try to control rivers. They tend to be more expensive.
Hard Engineering: Dams and Reservoirs
+ Produce electricity;
+ Attract tourists;
- Expensive;
- Dams trap sediment which decreases water capacity;
- Habitats flooded —> rotting vegetation —> releases methane (greenhouse gas);
- Settlements lost —> displacing people (in developing countries, people often don’t have a say or are consulted)
Hard Engineering: River Straightening and Dredging
+ More water held in channel;
+ Reduce flood risk in built-up areas;
- Dredging needs to be done frequently;
- Speeding up river increases flood risk downstream
Hard Engineering: Embankments
+ Cheap
+ Allows for flood water to be contained within river
- Looks unnatural
- Water speeds up, increase flood risk downstream
Hard Engineering: Flood Relief Channels
+ Removes excess water from river channel to reduce flooding;
- Expensive
- Relief channel may also flood due to continuous rising water levels —> other areas flooded instead
Soft Engineering
Involves a natural approach to managing river flooding with no artificial structures
Soft Engineering: Flood Warnings and Preparation
+ People have time to protect their properties (eg, with sandbags);
+ Many possessions can be saved, resulting in fewer insurance claims;
- Not everyone may be able to access the warnings;
- Flash floods may happen to quickly for a warning to be effective;
- They do not stop flooding, just warn people
Soft Engineering: Floodplain Zoning
+ More expensive buildings and land uses are farther away, so reduced flood risk;
+ Less damage caused —> fewer insurance claims;
- Not always possible to change existing land uses;
- Planners have to decide wha type of flood to plan for
Soft Engineering: Planting Trees (Afforestation)
+ Intercepts water;
+ Less surface run-off;
- Loss of potential grazing land;
- May look artificial
Soft Engineering: River Restoration
\+ New animal habitats; \+ Attractive —> boosts tourism; \+ Reduces flooding downstream; - Loss of potential grazing land; - Expensive; - Not always practical or effective
Soft Engineering: Earthen Embankments
\+ Provide habitats; \+ Attractive walkways; \+ Increased river capacity: \+ Cheap; - Prone to erosion; - High maintenance cost; - Give sense of false security
