flood risk and hydrographs

Question 1

describe the location of the River Tees:

Answer 1

• north of England
• source is located in the Pennines
• flows east to its mouth, joins the North Sea

Question 2

describe the River Tees in its upper course:

Answer 2

• hard, impermeable rocks
• vertical erosion formed a v-shaped valley
• ‘High Force’, UK’s largest waterfall (by volume, when in full force), is located in the Tees’ upper course.
• band of hard rock (whinstone) is located above an area of soft rock (sandstone and shale), creating the waterfall.

Question 3

describe the River Tees in its middle course:

Answer 3

• begins lateral erosion, forming meanders

Question 4

describe the River Tees in its lower course:

Answer 4

• the meanders are much larger, oxbow lakes have formed
• there are also levees, which have formed when the river has previously flooded
• has a large estuary, with mudflats and sandbanks, supporting wildlife in the area.

Question 5

what is river discharge?

Answer 5

the volume of water flowing in a river per second. (measured in cumecs)

Question 6

what is the difference between water infiltration and percolation?

Answer 6

infiltration: water seeping from the surface into the soil.
percolation: water seeping from the soil into permeable rock.

Question 7

what is the difference between streamflow, throughflow and groundwater flow?

Answer 7

streamflow: water flowing in the river channel.
throughflow: water flowing downhill through soil.
groundwater flow: water flowing through permeable rock.

Question 8

how can surface run-off affect floodrisk?

Answer 8

surface run-off is rapid. if this is increased, the flood risk increases, as the river is likely to reach its bankfull capacity faster.

Question 9

how can precipitation increase flood-risk?
(physical)

Answer 9

PROLONGED RAINFALL:
- saturates the soil
- reduces infiltration
- increases surface run-off
- increases river discharge

INTENSE, SUDDEN RAINFALL:
- infiltration doesn’t occur fast enough
- increases surface run-off
- increases river discharge

Question 10

define ‘transpiration’:

Answer 10

evaporation of water from plants.

Question 11

how can geology within the drainage basin increase flood risk?
(physical)

Answer 11

• impermeable soil and rock doesn’t allow infiltration or percolation
• increases surface run-off
• increases river discharge

Question 12

how can the relief of the drainage basin increase flood risk?
(physical)

Answer 12

• steep valley sides means that infiltration will not occur fast enough
• increases surface run-off due to gravity
• increases river discharge
• however, low-lying areas are also at risk. the gradient is not steep enough to remove flood water.

Question 13

how can urbanisation affect flood risk?
(human)

Answer 13

• buildings and roads are made from impermeable material (e.g. concrete, tarmac)
• reduces infiltration
• increases surface run-off
• increases river discharge

Question 14

how can deforestation within the drainage basin increase flood risk?
(human)

Answer 14

• removing trees reduces interception, vegetation storage and transpiration
• increases the amount of precipitation that reaches the surface
• increases surface run-off
• increases river discharge

Question 15

what is a hydrograph?

Answer 15

it shows how a river discharge (at a certain point within the river) changes overtime, in relation to precipitation.

Question 16

what is lag time on a hydrograph?

Answer 16

the time delay between the peak rainfall and the peak discharge. there’s a delay because not all of the rain falls directly into the river channel. it will either flow over the surface (rapid) or flow underground (slower).

Question 17

what is the rising limb and falling limb on a hydrograph?

Answer 17

RISING LIMB:
- increase in river discharge as the rainwater enters the channel
- the steeper the line, the faster rainwater is entering

FALLING LIMB:
- the decrease in river discharge as the river returns back to normal (base flow)

Question 18

how can the relief of the drainage basin affect the hydrograph results?

Answer 18

• steeper valleys will reduce infiltration and increase surface run-off
• rainwater will reach the river channel faster, reducing the lag time
• this will create a steeper rising limb and higher peak discharge

Question 19

how can the geology of the drainage basin affect the hydrograph results?

Answer 19

• impermeable soils and rock will reduce infiltration/percolation and increase surface run-off
• rainwater will reach the channel faster, reducing lag time
• this will create a steeper rising limb and higher peak discharge

Question 20

how can urbanisation of the drainage basin affect the hydrograph results?

Answer 20

• increasing buildings and roads increases impermeable surfaces
• this will reduce infiltration and increase surface run-off
• rainwater will reach the channel faster, reducing lag time
• this will create a steeper rising limb and higher peak discharge

Question 21

how can deforestation of the drainage basin affect the hydrograph results?

Answer 21

• removing trees reduces interception and transpiration
• this increases surface run-off, as more rainwater reaches the surface
• rainwater will reach the channel faster, reducing lag time
• this will create a steeper rising limb and higher peak discharge