flood risk and hydrographs Flashcards
describe the location of the River Tees:
- north of England
- source is located in the Pennines
- flows east to its mouth, joins the North Sea
describe the River Tees in its upper course:
- 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.
describe the River Tees in its middle course:
- begins lateral erosion, forming meanders
describe the River Tees in its lower course:
- 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.
what is river discharge?
the volume of water flowing in a river per second. (measured in cumecs)
what is the difference between water infiltration and percolation?
infiltration: water seeping from the surface into the soil.
percolation: water seeping from the soil into permeable rock.
what is the difference between streamflow, throughflow and groundwater flow?
streamflow: water flowing in the river channel.
throughflow: water flowing downhill through soil.
groundwater flow: water flowing through permeable rock.
how can surface run-off affect floodrisk?
surface run-off is rapid. if this is increased, the flood risk increases, as the river is likely to reach its bankfull capacity faster.
how can precipitation increase flood-risk?
(physical)
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
define ‘transpiration’:
evaporation of water from plants.
how can geology within the drainage basin increase flood risk?
(physical)
- impermeable soil and rock doesn’t allow infiltration or percolation
- increases surface run-off
- increases river discharge
how can the relief of the drainage basin increase flood risk?
(physical)
- 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.
how can urbanisation affect flood risk?
(human)
- buildings and roads are made from impermeable material (e.g. concrete, tarmac)
- reduces infiltration
- increases surface run-off
- increases river discharge
how can deforestation within the drainage basin increase flood risk?
(human)
- removing trees reduces interception, vegetation storage and transpiration
- increases the amount of precipitation that reaches the surface
- increases surface run-off
- increases river discharge
what is a hydrograph?
it shows how a river discharge (at a certain point within the river) changes overtime, in relation to precipitation.
what is lag time on a hydrograph?
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).
what is the rising limb and falling limb on a hydrograph?
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)
how can the relief of the drainage basin affect the hydrograph results?
- 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
how can the geology of the drainage basin affect the hydrograph results?
- 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
how can urbanisation of the drainage basin affect the hydrograph results?
- 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
how can deforestation of the drainage basin affect the hydrograph results?
- 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
