A presentation of the first subchapter (Drainage Basin Systems) from the first chapter (Hydrology and Fluvial Geomorphology) of Revision for Geography AS Cambridge exam.

1. ASGEOGRAPHYREVISION
HYDROLOGYAND
FLUVIALGEOMORPHOLOGY
1.1 DRAINAGEBASINSYSTEMS

2. KEYTERMSANDDEFINITIONS
Hydrology is the study of water as it moves on, under and through the
Earth’s surface.
The hydrological cycle (also called the water cycle) is the movement of
water between air, land and sea. It varies from place to place and over
time.
Precipitation is the conversion and transfer of moisture in the
atmosphere to the land. It includes all forms of rainfall, snow, frost, hail
and dew.

4. KEYTERMSANDDEFINITIONS
Interception is the precipitation that is collected and stored by
vegetation.
Overland flow (or surface run-off) occurs in two cases:
1 when the intensity of precipitation that reaches the surface exceeds the
infiltration capacity of the soil. This process is known as Hortonian overland
flow
2 when the combination of precipitation intensity and duration saturates the
soil and raises the water table to the surface. This process is known as
saturation overland flow.

6. KEYTERMSANDDEFINITIONS
Infiltration is the movement of water downwards from the surface into
the soil.
Evaporation refers to water from the ground or a lake that changes into
a gas.
Transpiration is water loss from vegetation to the atmosphere.
Evapotranspiration is the combined losses of evaporation and
transpiration.
Drainage basin is the area of land drained by a river system (a river and
its tributaries).
Interception is the precipitation that is collected and stored by
vegetation.

8. KEYTERMSANDDEFINITIONS
Throughfall is water flowing off wet leaves onto the ground.
Stemflow is water flowing down the trunks of trees and stems of
grasses and shrubs.
Percolation is the movement of water down into the groundwater
zone.
Throughflow is water flowing through the soil down to the
groundwater zone.
Baseflow is the movement of water through rock. It is the slowest form
of such water movement, and accounts for the constant flow of water
in rivers during times of low rainfall.

9. KEYTERMSANDDEFINITIONS
Water table is the upper layer of permanently saturated pore spaces in
the groundwater zone.
Groundwater is water stored underground in a permeable rock, e.g.
chalk or sandstone. The water emerges at the surface as springs and
streams. The groundwater’s upper level is called the water table.
Layers of rock that are filled with groundwater are called aquifers.
Recharge is the ‘topping up’ of groundwater levels following
abstraction.
Capillary movement is the upward movement of water in a soil. It
usually occurs in climates where evaporation exceeds precipitation
either annually or seasonally.
Springs are where water seeps directly out of the ground where an
aquifer reaches the ground surface.

10. TOPICSUMMARY
The hydrological cycle refers to the cycle of water between
atmosphere, lithosphere and biosphere.
The drainage basin system is an open system as it allows the
movement of energy and matter across its boundaries.
Water can be stored at a number of stages or levels within the cycle.
These stores include vegetation, surface, soil moisture, groundwater
and water channels.
Human modifications are made at every scale.

11. TOPICSUMMARY
Precipitation is the main input into the drainage basin system. It is the
transfer of moisture from the atmosphere to the land.
Interception refers to water that is caught and stored by vegetation.
Evaporation is the process by which a liquid or a solid is changed into a
gas.
Factors affecting evaporation include meteorological factors such as
temperature, humidity and wind speed.
Transpiration is the process by which water vapour escapes from
plants.
The combined effects of evaporation and transpiration are normally
referred to as evapotranspiration (EVT).

13. TOPICSUMMARY
Infiltration is the process by which water soaks into or is absorbed by
the soil.
Soil moisture refers to the subsurface water in the soil.
Groundwater refers to subsurface water. Groundwater accounts for
96.5 per cent of all freshwater on the earth.
Aquifers are rocks that contain significant quantities of water.

15. ADDITIONALWORK
1. Outline the ways in which human activities have modified the
hydrological cycle.
2. Describe and explain the role of vegetation in the hydrological cycle.
3. Discuss the importance of groundwater.
4. Describe and explain how the hydrological cycle varies between
different geographic regions.

16. SUGGESTEDWEBSITES
http://geography.about.com/cs/waterhydrology/ for links to some
excellent sites on hydrology and rivers.
Try the matching quiz (for the hydrological cycle) at:
http://highered.mcgraw-
hill.com/sites/0072402466/student_view0/chapter10/matching_quiz.
html
www.nwlg.org/pages/resources/geog/hydro_cycle/hydro/cycle.htm
for animations on the hydrological cycle.
http://geography.about.com/cs/waterhydrology/ for links to some
excellent sites on hydrology and rivers.