Case study theme 2

Question 1

Causes of river flooding

Answer 1

Named river: river Valency (on the northern coast of Cornwall, South West of England)
- Deforestation, trees have been removed from valley sides => less interception from precipitation => more surface runoff (water can’t infiltrate) => no water lost from evaporation from leaves; water not taken from the ground by roots
- Confluence just before Boscastle with river Jordan => lots of water joined at once => A high discharge level in the river during periods of heavy rainfall
- Urbanisation=> building materials such as concrete, brick, steel are impervious surfaces => water cannot infiltrate like on turf or soil => Increases surface run-off => water reaches the river quicker => build up lots of discharge in short period

Question 2

Effects of the flooding by a river

Answer 2

Named river: river valency
- Gov had to spend 10m GBD to build defences to ensure that flood is not going to happen again => affect the local economy => lower quality of public services provide (shortage of cash) => lowers peoples’ SOL
- Increase in premiums paid by local residents to insurance in future => greater risk of property being damaged => more expenses paid each month => fewer money for physiological needs => lower standard of living, suffer from malnutrition
- Less money for local shops and services => main function is tourism => less tourists travel to dangerous destination => less consumer for these services => less income for people to paid on their basic needs and amenities

Question 3

Management and response of a flooded river

Answer 3

Named river: River valency
- Increase in channel size; dredged the riverbed to make the river channel deeper => increases the amount of discharge that the river can carry => lowers the chance of river overflowing banks => less likely to flood
- Afforestation, increase interception as trees are planted to the valley sides => intercepted the precipitation as moistures fall down the leaf & being evaporated => decreases surface run-off. Water is also taken from the ground by roots.
- Raised the car park area allows a higher column of water flowing through the area => reduces damage to vehicles due to ingress of water to the engines => lowers costs paid by insurance => offering lower premiums for citizens to be paid.

Question 4

Ox-bow lake formation

Answer 4

• An ox-bow lake forms where rivers meander in the lower course, as they near their mouths.
• When river goes around a meander, most of the water is directed towards the outside bend => the velocity of river on outside of meander increases => giving river energy to carry greater load
• With load by corrasion (load bangs & scraps channel to erode it) and the sheer force of water (hydraulic action) => river laterally erodes on the outside bank => becomes undercut leaving a river cliff; which collapse over time
• On the inside bend, river’s current is slower => slow velocity only enables transportation of small sediment => an area of deposition => forming a point bar / slip-off slope
• WIth erosion on the outside bend and deposition on the inside => the meander gets more sinuous; eventually the channel moves to a position where the meander neck is very narrow => Can be cut through at times of high discharge => leaving the remains of the meander as a small lake (ox-bow); generally dry up

Question 5

Formation of waterfall

Answer 5

• Waterfall occurs in the upper course of a river, where more resistant rock (limestone) at Ban Gioc waterfall in Cao Bang, Vietnam overlies less resistant rock (erodes much quicker)
  -Hydraulic action erodes the less resistant rocks as force of water and air pushed into crack breaks rock
• Abrasion, rocks being dragged along the river floor so they being eroded
• Corrosion, process where rocks are being eroded to chemical
• Erosion speed in less resistant rock occurs a lot faster than more resistant rock => soft rock retreats due to the splashing water and eddie currents in the plunge pool; undercuts the hard rock above, eventually created an unsupported overhang.
• As this retreat continues to happen, eventually, the overhang collapses into plunge pool due to gravitational force, the downward force acting on any object near the Earth surface.
• As the process is repeated for many times, the channel gradually retreated upstream, closer to the source => forming steep sided valley on both side called gorge.