This document discusses drainage basins and the water cycle within a typical basin. It explains that a drainage basin is the area where precipitation flows into a river system. Water enters the basin as precipitation and leaves through evaporation, transpiration, and river discharge. The document outlines the various inputs, storage mechanisms, flows and processes, and outputs involved in the water cycle within a drainage basin. It describes precipitation, interception, vegetation storage, surface storage, groundwater storage, channel storage, and more. Finally, it discusses the water balance of a basin and how inputs and outputs vary seasonally.

1. Rivers

2. Drainage Basins
• Are local open systems within the closed global
hydrological cycle
• A river’s drainage basin is the area surrounding the river
where the rain falling on the land flows into that river.
This area is also called the river’s catchment
• The boundary of a drainage basin is the watershed- any
precipitation falling beyond the watershed enters a
different drainage basin
• Drainage basins are open systems with inputs and
outputs
• Water comes into the system as precipitation and leaves
via evaporation, transpiration and river discharge

3. A Typical Drainage Basin System

4. Inputs- water coming into the system
• Precipitation includes all the ways moisture
comes out of the atmosphere
• Precipitation is mainly rain, but also includes
snow, hail, dew and frost

5. Storage- water stored in the system
• Interception
• Vegetation
• Surface
• Groundwater
• Channel

6. Interception
• Interception is when some precipitation lands
on vegetation or other structures, like
buildings and concrete or tarmac surfaces,
before it reaches the soil
• Interception creates a significant store of
water in wooded areas
• Interception storage is only temporary
because the collected water evaporates
quickly

7. Vegetation
• Vegetation storage is water that’s been taken
up by plants
• It’s all the water contained in plants at ny one
time

8. Surface
• Surface storage includes water in puddles
(depression storage), ponds and lakes

9. Groundwater
• Groundwater storage is water stored in the
ground, either in the soil (soil moisture) or in
rocks
• The water table is the top surface of the zone
of saturation – the zone of soil or rock where
all the pores in the soil or rock are full of
water
• Porous rocks (rocks with holes in them) that
hold water are called aquifers

10. Channel
• Channel storage is the water held in a river or
stream channel

11. Flows and Processes- water moving
from one place to another
• Surface runoff
• Throughfall
• Stemflow
• Throughflow
• Infiltration
• Percolation
• Groundwater flow
• Baseflow
• Interflow
• Channel flow

12. Surface runoff
• Surface runoff/ overland flow is water flowing
over the land
• It can flow over the whole surface or in little
channels
• Surface runoff is common in arid areas where
torrential rain falls on hard baked land

13. Throughfall
• Throughfall is water dripping from one (or
other plant part) to another

14. Stemflow
• Stemflow is water running down a plant stem
or tree trunk

15. Throughflow
• Throughflow is water moving slowly downhill
through the soil
• Throughflow is faster through ‘pipes’- things
like cracks in the soil or animal burrows

16. Infiltration
• Infiltration is water soaking into the soil
• Infiltration rates are influenced by soil type,
soil structure and how much water’s already
in the soil
• In a heavy storm, water can’t infiltrate fast
enough, so it flows over the surface

17. Percolation
• Percolation is water seeping down through
the soil into the water table

18. Groundwater flow
• Groundwater flow is water flowing slowly
below the water table through permeable
rock
• Water flows through most rocks, but rocks
that are highly permeable with lots of joints
(gaps that water can get through) can have
faster groundwater flow, e.g. limestone

19. Baseflow
• Baseflow is groundwater flow that feeds into
rivers through river banks and river beds

20. Interflow
• Interflow is water flowing downhill through
permeable rock above the water table

21. Channel flow
• Channel flow is the water flowing in the river
or stream itself
• This is also called the river’s discharge

22. Outputs- water leaving the system
• Evaporation
• Transpiration
• Evapotranspiration
• River discharge

23. Evaporation
• Evaporation is water turning into water
vapour- turning from a liquid to a gas

24. Transpiration
• Transpiration is evaporation from plant
leaves- plants and trees take up water though
their roots and transport it to their leaves
where it evaporates it into the atmosphere

25. Evapotranspiration
• Evapotranspiration is the process of evaporation
and transpiration together
Potential Evapotranspiration
PET is the amount of water that could be lost by
evapotranspiration
Actual evapotranspiration is what actually happens
e.g. in a desert, PET is high (because heat increases
the amount of evaporation) but actual transpiration
is low because there isn’t that much moisture in the
first place

26. River discharge
• River discharge, or river flow is another output

27. The Water Balance
• The water balance shows the balance
between inputs and outputs
• Water balance is worked out from inputs
(precipitation) and outputs (channel discharge
and evapotranspiration)
• The water balance affects how much is stored
in the basin

28. The general water balance in the UK
shows seasonal patterns:
1) In wet seasons, precipitation exceeds
evapotranspiration. This creates a water surplus. The
ground stores fill with water so there’s more surface
runoff and higher discharge, so river levels rise
2) In drier seasons, precipitation is lower than
evapotranspiration. Ground stores are depleted as
some water is used (by plants and humans) and some
flows into the river channel, but isn’t replaced by
precipitation
3) So, at the end of a dry season, there’s a deficit of
water in the ground. The ground stores are recharged
in the next wet season i.e. autumn

29. Water balance for a temperate zone
e.g. UK