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Rivers 1
- River Fluctuation
- The discharge of a
river is the volume of
water passing down
a river. It can
fluctuate a lot in a
matter of hours in
response to periods
of rain.
- Storm Hydrography: used to show
how a river responds to a period of
rainfall. Rivers that respond rapidly
to rainfall have a high peak and
short lag time and are referred to
as flashy. A lower peace and long
lag time shows a delayed
hydrography
- Precipitation: any source of moisture
reaching the ground
- Interception: water
being prevented from
reaching the surface by
trees/grass
- Surface Storage:
water held on
the ground
surface
- Soil
Moisture:
water held
in the soil
layer
- Percolation:
water seeping
deeper below the
surface
- Groundwater: water stored
in the rock
- Transpiration: water lost through
pores in vegetation
- Evaporation: water
lost from
ground/vegetation
surface
- Evaporation: water
lost from
ground/vegetation
surface
- Transpiration: water lost through
pores in vegetation
- Groundwater: water stored
in the rock
- Percolation:
water seeping
deeper below the
surface
- Soil
Moisture:
water held
in the soil
layer
- Infiltration:
water sinking
into soil/rock
from the ground
surface
- Surface Storage:
water held on
the ground
surface
- Interception: water
being prevented from
reaching the surface by
trees/grass
- The discharge of a
river is the volume of
water passing down
a river. It can
fluctuate a lot in a
matter of hours in
response to periods
of rain.
- River DIshcharge
- Influenced by rainfall, temperature, previous
weather conditions, relief, rock type and
human land use
- Lot of rain falling causes high river
levels, while less rainfall results in
lower river levels.
- High amounts of rain saturate the soil and
underlying rock. Drizzle: time for water to
infiltrate the soil and underlying roc, freeing up
more space for rain
- Temperature affects the loss of
water from the drainage basin and
therefore the level of discharge.
When temperatures are higher, there
is greater water loss via evaporation
and transpiration, so river levels go
down.
- Previous weather conditions
also have an impact on river
discharge. If its dry, it will take
longer for the water to reach
the river and the amount will
be less if there had been a
number of wet days
- Deforestation: if trees are removed,
water reaches the surface faster and the
trees do not extract water from the
ground. Urbanisation: expanding towns
create an impermeable surface.
- Deforestation: if trees are removed,
water reaches the surface faster and the
trees do not extract water from the
ground. Urbanisation: expanding towns
create an impermeable surface.
- Steep slopes encourage fast
run-off as the water spills
rapidly downwards due to
gravity
- Rock type determines how much water
infiltrates and how much stays on the
surface. Areas with impermeable rocks,
have more surface rivers than permeable
rocks, which are porous, or pervious.
- Rock type determines how much water
infiltrates and how much stays on the
surface. Areas with impermeable rocks,
have more surface rivers than permeable
rocks, which are porous, or pervious.
- Temperature affects the loss of
water from the drainage basin and
therefore the level of discharge.
When temperatures are higher, there
is greater water loss via evaporation
and transpiration, so river levels go
down.
- Influenced by rainfall, temperature, previous
weather conditions, relief, rock type and
human land use
- Floods
- Floods occur
when a river
bursts its banks.
It is an extreme
situation due to
high levels of
flow. Building on
floodplains
results in
property being
damaged and
lives being lost
in what
becomes a
hazard.
- Rivers flood due to prolonged rainfall,
heavy rain, snowmelt and steep relief.
People often unintentionally increase
the likelihood and severity of flooding.
Mainly due to deforestation and
construction work
- Floods appear to be an
increasingly frequent
event
- The effects of flooding vary according to their size and
location. The impact tends to be more severe in LEDCs.
responses are generally more immediate in countries at
further stages of development and the attempts made to
reduce the effects come from within the affected area or
country. In LEDCs attempts made to reduce the effects may
be delayed and require international effort.
- Floods appear to be an
increasingly frequent
event
- Rivers flood due to prolonged rainfall,
heavy rain, snowmelt and steep relief.
People often unintentionally increase
the likelihood and severity of flooding.
Mainly due to deforestation and
construction work
- Floods occur
when a river
bursts its banks.
It is an extreme
situation due to
high levels of
flow. Building on
floodplains
results in
property being
damaged and
lives being lost
in what
becomes a
hazard.
- Case Studies
- LEDC: Bangladesh 1998
- Effects: The water in Dhaka, was 2 metres
deep and covered three-quarters of the city.
Electricity was cut off for several weeks and
there was no safe drinking water. 7 million
homes were destroyed and over 25 million were
homeless. The death toll was over 1300. There
were shortages of food and medicines. 2 million
tonnes of rice was destroyed. Thousands of
kilometres of roads, a third of the railways and
Dhaka's airport were all flooded
- Responses: Emergency supplies for
food, water tents and medicines.
Aid from other countries. Reduce
Deforestation in Nepal and the
Himalayas. Construction of dams,
and boats to rescue people. Repair
and Rebuild houses. Assistance
from the UN and other charities.
International food aid programmes.
Fodder for livestock, Farmers
provide with free seeds and water
purification tablets:
- Responses: Emergency supplies for
food, water tents and medicines.
Aid from other countries. Reduce
Deforestation in Nepal and the
Himalayas. Construction of dams,
and boats to rescue people. Repair
and Rebuild houses. Assistance
from the UN and other charities.
International food aid programmes.
Fodder for livestock, Farmers
provide with free seeds and water
purification tablets:
- Effects: The water in Dhaka, was 2 metres
deep and covered three-quarters of the city.
Electricity was cut off for several weeks and
there was no safe drinking water. 7 million
homes were destroyed and over 25 million were
homeless. The death toll was over 1300. There
were shortages of food and medicines. 2 million
tonnes of rice was destroyed. Thousands of
kilometres of roads, a third of the railways and
Dhaka's airport were all flooded
- MEDC: Boscastle, UK
2004
- Effects: Destroyed homes, stress and anxiety
for local people,. Cars belonging to more than
1,000 people were washed away. 25 business
properties were destroyed. Bridges and roads
were damaged. 4 footbridges washed away.
Area relies on tourism for 90% income, most of
which earned in summer months.. Insurance
companies paid out £20 million to repair.
- Responses: Major incident declared at 5pm. RAF
search and rescue services were alerted to rescue
trapped people. Non-one died cut to the rapid response
of the emergency services. Trees near river removed.
Rescue boats to rescue trapped people. Radio and
television coverage
- Responses: Major incident declared at 5pm. RAF
search and rescue services were alerted to rescue
trapped people. Non-one died cut to the rapid response
of the emergency services. Trees near river removed.
Rescue boats to rescue trapped people. Radio and
television coverage
- Effects: Destroyed homes, stress and anxiety
for local people,. Cars belonging to more than
1,000 people were washed away. 25 business
properties were destroyed. Bridges and roads
were damaged. 4 footbridges washed away.
Area relies on tourism for 90% income, most of
which earned in summer months.. Insurance
companies paid out £20 million to repair.
- LEDC: Bangladesh 1998
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