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THE DRAINAGE BASIN HYDROLOGICAL
CYCLE: THE WATER BALANCE
· Where
CASE STUDYever OF
you are on the world,
DRAINAGE BASIN you are within a drainage
= MISSISIPPI-MISSOURI
basin. A drainage basin is an area of land (catchment area)
(USA)
drain over
-Drains by a 3,225,000km²
river and it's tributaries.
of the North American Continent
-Has a discharge
· Drainage basinsofare
12,743 m³/s offrom
separated water each other by ridges of
-Carries
higher aland
daily load of
called 396,000 tonnes
watersheds. of sedimentfalling
Any precipitation into the delta
-Flooding
beyond was caused by
a watershed heavy
will drainrainfall,
into the high tides and storm
neighbouring basin.
surges
System from hurricane
Theory KatrinaBasin
of a Drainage
-The drainage basin directly provides water for over 18 million
The systems theory is used as a way of explaining how the drainage basin or
people
ecosystems work. Classified into three types of components:
-Supplies an estimated 92% of all agricultural exports in the USA
Isolated: there is no input or output of energy or matter (the universe is
probably the only example of this).
Closed: there is input, transfer and output of energy but not of matter or mass
(some might consider the planet an example of this).
Open: there are inputs and outputs of both energy and matter (most
environmental systems are thought to be examples of this).…read more

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THE DRAINAGE BASIN HYDROLOGICAL
CYCLE: THE WATER BALANCE
CONTINUED
· When inputs and outputs are
balanced, it is a state of dynamic
equilibrium. Most systems are rarely
balanced but continuously changing
to reach this stage.
An example of this
could be, prolonged rainfall will
increase discharge and velocity,
causing more erosion.
· Feedback loops are where deviations
in inputs and outputs move systems
away from their balanced state.
Negative feedback loops exist where
changes are eventually met and
corrected to lead back to the original
state. Positive feedback loops exist
where one change away from the
original state triggers another
change leading further away from
the original state.…read more

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The UK Climate
MODEL OF WATER BUDGET
In a temperate climate such as the UK, precipitation usually exceeds evapotranspiration so that
over a year there is a positive water budget / water balance. During the winter months when
precipitation is relatively high and evapotranspiration and temperatures are low there is a soil
· The
moisture balance
(amount between
of water & water vapour in an unsaturated soil) surplus. This is due to there
being harder ground, meaning more runoff and higher river levels. This is constantly changing
water inputs and outputs
through the seasons meaning the river levels are constantly changing.
of a drainage basin may be
shown as a water budget
graph.
Water budget P = Q + E +/-
change in storage
Where:
P = precipitation
Q = runoff
E = evapotranspiriation (the
loss of water from a
drainage basin into the
atmosphere from the
leaves of plants).…read more

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THE STORM HYDROGRAPH
The storm hydrograph is created by continuously taking measurements of a rivers
discharge to measure how it changes from hour to hour. The fluctuations in
channel discharge are recorded on a hydrograph. The graph below allows us to
examine a relationship between the rainfall event and the discharge. It shows the
discharge before, during and after the event.
Base flow…read more

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CASE STUDY, RIVER EDEN, CARLISLE,
CUMBRIA
· The case study for
flooding in the UK is
the river Eden,
Carlisle.
· The flood hydrograph
shows just how
quickly a river can
respond to a major
rainfall
· The flood killed 3
people and left
thousands homeless
· The cause of the
flooding is debatable…read more

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