Water in a river drainage system
To accompany Lesson 3.1 of the Water resources teacher guide and lesson plans:
Balancing priorities: agriculture and the environment – The Murray-Darling Basin
© Commonwealth of Australia, 2011
How does water flow in this system?
US Department of Agriculture
© Commonwealth of Australia, 2011
Water in a river drainage system: input, transfer, storage
and outputs
inputs
transfer storage
outputs
© Commonwealth of Australia, 2011
Inputs
Precipitation (rain, hail or snow) enters the river
drainage basin.
This precipitation is the input of water into the
system (inflows).
US Department of Agriculture
© Commonwealth of Australia, 2011
Transfer: water movement through the basin
Some of the precipitation flows across the ground
(surface run-off) into rivers and adds to streamflow.
Surface run-off also flows into lakes, dams and
reservoirs.
Some of the water soaks into the ground,
entering gaps between soil particles (infiltration).
Some of the water that has soaked underground travels close
to the land surface and soon emerges into streambeds.
US Department of Agriculture
© Commonwealth of Australia, 2011
Gravity causes the remaining water to seep deep
underground through soil and rock via the process of
percolation.
Transfer and storage: below ground flows
US Department of Agriculture
© Commonwealth of Australia, 2011
The water that infiltrates the soil and seeps deeper
below
the surface eventually
the water table,
Groundwater
that seeps meets
deep underground
forms
which
is the
layer underground
where the soilwater
is saturated.
In this
huge
natural
storage areas
saturated
the small
and spaces
between
calledlayer,
aquifers,
wherecracks
the water
saturates
porous
the rock
filledmoves
with water.
This isinwhat
rock.particles
Typically,are
water
very slowly
an we
call groundwater.
aquifer and can take thousands or even millions of
years to move back into the river drainage system.
Storage: benefits of groundwater
• The slow trickle of groundwater into streams
and wetlands provides essential water during
periods of low rainfall.
• Groundwater stores provide an alternative
source of water to water captured from
surface water run-off. Groundwater is brought
to the surface by drilling underground into the
saturated zone.
© Department of Sustainability, Environment, Water, Population and Communities, 2011
Output
Large amounts of water will also re-enter the
atmosphere as water vapour.
The final release of water out of the river drainage
system is the output (outflows).
US Department of Agriculture
Often water flows through a river drainage
system and out to sea.
© Department of Sustainability, Environment, Water, Population and Communities, 2011
Output: evaporation and
evapotranspiration
• Evaporation of liquid water into a gas (water
vapour) occurs from water stored in oceans,
lakes, dams, wetlands and river channels.
• Water also evaporates from the soil surface.
• Plants draws up water from soils through their
roots. The water vapour exits the plants via their
leaves (transpiration).
• The combined loss of water to the atmosphere
through evaporation and transpiration is called
evapotranspiration.
© Commonwealth of Australia, 2011