Slide 4: The River Cuckmere (Sussex) enters the sea at Cuckmere Haven
Slide 4: The River Cuckmere (Sussex) enters the sea at Cuckmere Haven
The Water Cycle
Stage One:
Evaporation and transpiration:
Evaporation is when the
sun heats up water in seas and oceans and turns it into water vapour or
steam (water H2O turns
into a gas). The water vapour or steam leaves the river, lake or ocean
and goes into the air.
Transpiration is the process
by which plants and trees lose water out of their leaves into the air.
Stage Two:
Convection and condensation:
The water vapour is heated
by the sun. In a process called convection it rises, because it is warmer
than the air above it.
Water vapour in the air
cools and changes back into liquid, forming clouds: this is called condensation.
Stage Three:
Precipitation occurs
when so much water has condensed that the air cannot hold it anymore. The
clouds get heavy and water falls back to the earth in the form of rain,
hail, sleet or snow. When the clouds meet cool air over land this acts
as a trigger for the rain to fall.
Stage Four:
Percolation and absorption:
The rain falls on the sea, land and lakes.
On land the rain sinks into
the soil and runs off hard rocks, and percolates (trickles or filters*)
through the softer porous rocks like the chalk on the Downs. (* like
a coffee percolator, water runs through the porous material but the coffee,
or soil, doesn’t).
On land the water is used
by the plants, crops and trees to grow. (Trees use lots of water.)
But the soil can only absorb
so much water before it floods, forms bogs and marshes or is channelled
into streams and rivers that flow out to sea.
Torrents, groundwater
and aquifers: On hard rocks the water bounces straight off in
torrents, which are fast streams that flow into rivers.
On chalk (like the downs)
the water flows through the soft rock and is stored underground. Water
stored underground is called groundwater and is stored in aquifers. The
water is trapped in the soil and soft porous rocks, sometimes open to the
air in ponds. Groundwater takes longer to flow out to sea by the way of
rivers and streams.