Hydrology

Question 1

What is evaporation?

Answer 1

water that is heated by the sun from liquid to gas and rises into the atmosphere

Question 2

What is evapotranspiration?

Answer 2

evaporation and transpiration happening at the same time

Question 3

what is percolation?

Answer 3

water flowing down from the soil into the bedrock

Question 4

what is abrasion?

Answer 4

wearing away of the bed and bank by the load carried by the river

Question 5

what is attrition?

Answer 5

wearing away of the load carried by a river, creates smaller and rounder objects

Question 6

what is hydraulic action?

Answer 6

force of air and water on the sides of river and in cracks

Question 7

what is cavitation?

Answer 7

force of air exploding; as fluids accelerate, pressure may drop causing bubbles to form which will implode in cracks and event mini jets of water

Question 8

What is corrosion?

Answer 8

removal of chemical ions, especially calcium

Question 9

How are different loads transported?

Answer 9

-smallest particles are carried in suspension as the suspended load
-salted load are bigger particles transported in a series of hops
-tracted load are pebbles shunted along the bed
-material is carried in solution as the dissolved load

Question 10

what is laminar flow?

Answer 10

-the flow will develop into layers in an efficient river, with the top and bottom slower than the middle
-some friction with air and friction with bank and bed

Question 11

what is turbulent flow?

Answer 11

-the flow will be turbulent with verticals and horizontal eddies in rivers with a less smooth base
- causes more erosion

Question 12

what is helicoidal flow?

Answer 12

-high pressure on the outside of a meander creates low pressure on the inside which creates a flow from one to the other
-spiral flow

Question 13

How is meander formed?

Answer 13

-alternating areas of fast and slow flow will develop, faster areas will have more erosive power and create deeper areas called pools and slower areas will be shallower riffles
-thalweg will be deflected by the riffles onto the bank and start to create erosion on the bank
-deeper pools become the outside of the meander with riffles between
-helicoidal flow will lead to deposition on the inside of the bend creating in a slip off slope with erosion creating a river cliff on the outside

Question 14

How is a arcuate delta formed?

Answer 14

weak currents, long shore drift and lots of material gives a gently shaped delta
e.g. Nile

Question 15

How is a cuspate delta formed?

Answer 15

stronger, opposing currents - pointy tooth like shape created
e.g. Ebro, Spain

Question 16

How is a birds foot delta formed?

Answer 16

Huge quantities of material creates a birds foot shape
e.g. mississippi

Question 17

How is a delta formed?

Answer 17

-where rivers meet the sea, deposition occurs
-if the currents are not strong enough to wash it away a delta will for,
-deposition is increased by flocculation - these are the particles that would otherwise not be deposited on the Hjölstrom curve, clay deposits make deltas very fertile

Question 18

How is a levee formed?

Answer 18

-when a river floods it suddenly loses efficiency, loses velocity and drops load heaviest first
- past flood the water cannot get back into the river so sinks into the flood plain, depositing alll of its lighter load (including clay)
-As the channel deepens, deposition occurs on the bed and raises it

Question 19

What are braised channels and how do they form?

Answer 19

-channel is divided by islands often vegetated and long lived
-occur on steep channel gradient, large proportion of course material, easily eroded bank material, highly variable discharge
- island of alluvial deposits forming shingle deposits

Question 20

CS: what are the causes of flooding in Bangladesh?

Answer 20

• deforestation in Nepal for fuel wool increases overland flow and soil erosion
  -snowmelt in himalaya meaning discharge is seasonal and affected by climate change
  -urbanisation of Ganges valley means more overland flow due to impermeable surfaces, less infiltration and shorter lag time (over 650mil population)
  -floodplains and delta, land is very flat and prone to flooding (75% is 5m of sea level)
  -cyclones in bay if bengal bring in storm surges which cause costal flooding
  -monsoon climate so seasonal heavy rainfall causes annual flooding
  -poor river management of dams in india and levees in bangladesh