Contents
Introduction
i
Table of contents
ii
Section 1: The water system
The hydrological cycle
Page 01
The water balance
Page 04
Section 2: Drainage basins and flooding
Drainage basins
Page 05
Discharge
Page 06
Hydrographs
Page 07
Floods
Page 10
Section 3: Management issues and strategies
Dams and reservoirs
Page 12
Floodplain management
Page 13
Groundwater management
Page 17
Freshwater wetland management
Page 18
Irrigation and agriculture
Page 20
Section 4: Competing demands for water
Conflicts at the local/national scale
Page 22
Conflicts at the international scale
Page 23
End of topic checklist
Page 24
Answers to IB exam focus questions
Page 25
List of Figures
Page 30
ii
IB Geography Freshwater | Issues and Conflicts
Exam hint! Stream flow and channel shape are not
the only factors influencing stream discharge.
Discharge is also affected by other variables, such as
rock and soil type, land use, relief and weather
conditions.
Discharge
Stream discharge and its relationship to stream flow and channel shape
Key
definition!
 Stream discharge is the amount of water that passes a given point of a stream per second. Discharge is
3






measured in cubic metres (m ) per second or cumecs.
The discharge of a river is directly related to stream flow (velocity) and channel shape (hydraulic radius) and is
given by the equation Q= w x d x v, where Q is discharge, w is channel width, d is channel depth and v is
channel velocity. The cross-sectional area of a stream can is the product of width and depth of the channel.
Discharge increases with increased stream flow (velocity) as streams with a faster flow can transport a greater
amount of water past a point over a given time.
Channel shape is best described by the hydraulic radius, which is the ratio of the cross-sectional area of a
stream to its wetted perimeter (the length of the bed and banks in contact with the river).
Rivers with a greater hydraulic radius (narrow, deep channels) are more efficient and thus have a greater
velocity and hence discharge than wide, shallow streams because less water is in contact with the wetted
perimeter, reducing friction and increasing the energy of the stream.
For example, stream A in figure 2.3 has a greater hydraulic radius than stream B because less water is in
contact with the beds and banks. As a result, stream A will have a greater discharge than stream B.
Stream discharge increases downstream because as a river moves from the upper course to its lower course,
additional water enters the river from tributary streams, surface runoff, throughflow and baseflow.
Stream A
Stream B
5m
Hydraulic radius = cross-sectional
area/wetted perimeter.
5m
2m
40/18 = 2.22
8m
2m
20m
40/24 = 1.67
Figure 2.3: Calculating the hydraulic radius for two streams of the same cross-sectional area.
IB exam focus
Q4. Define the term stream discharge. [2]
Q5. Outline the relationship between channel shape and
stream discharge. [3]
6
IB Geography Freshwater | Issues and Conflicts
Exam hint! Do not confuse the term, ‘groundwater’
with ‘subsurface water’. Groundwater refers to the
water stored in the saturated phreatic zone,
whereas subsurface water refers to the entirety of
water stored beneath the surface (soil water in the
unsaturated vadose zone and groundwater).
Groundwater management
The functioning and management of artesian basins and aquifers
Key

definition!
Groundwater is water held under the surface in the phreatic (saturated zone) beneath the water table.
 Groundwater is an important component of the global hydrological cycle and is the world’s largest store of
freshwater, storing over 90% of the total supply. Groundwater is stored in aquifers and artesian basins.
 Aquifers are porous rocks such as sandstone and limestone that contain significant quantities of water.
Aquifers can transmit and store water effectively. Aquitards are rock formations that are less permeable and
transmit water more slowly.
 An artesian basin is a basin containing an aquifer confined by two aquitards or layers of impermeable rock (see
diagram below). As a result, artesian basins are under high hydrostatic pressure and if a bore was sunk into
the ground, water would flow to the surface via capillary action without pumping, forming an artesian well. As
more water is abstracted from the well, the hydrostatic pressure in an artesian basin decreases.
 Aquifers and artesian basins are recharged both naturally and artificially, replenishing groundwater storage.
Natural recharge includes infiltration and percolation after precipitation or snowmelt and seepage from river
channels or adjacent aquifers. However, artificial recharge includes leakage from irrigation channels and
reservoirs or the pumping of water into aquifers.
Figure 3.5: Artesian basin
The environmental impacts of groundwater abstraction
 Falling water tables: occur in regions where water is being pumped from beneath the ground at greater rates
than it is being replenished/recharged by rainfall. For example, intensive use of groundwater in Australia for
over a century has caused the upper level of the Great Artesian Basin to fall by 120m since it was first tapped.
 Salt-water intrusion: in some coastal areas, where water tables have fallen to or below sea level, seawater can
enter into and contaminate groundwater supplies. This in turn causes salinization, which contaminates
drinking water and inhibits agriculture (salt is toxic to plants). For example, over-abstraction of groundwater
on the Gaza Strip, Israel has led to salinization of irrigation water, which has compromised the production of
citrus trees (an important cash crop), as they are highly salt-intolerant.
 Ground subsidence: as water tables fall and the water content of the soil is reduced, which in extreme cases
can cause the soil to collapse. For example, the city of Bangkok, Thailand is placed above the Lower Chao
Phraya Basin (underlain by a layer of clay) is currently subsiding at a rate of 5-10 cm per year due to the heavy
weight of stone houses and skyscrapers as well as high rates of groundwater abstraction. This subsidence has
led to increased flooding in the city, such as the 2011 floods, which killed 815 people. Also, it is likely that parts
of the city will be completely submerged by 2030, displacing 7 million people if the government fails to restrict
groundwater usage.
 River discharge reduction: groundwater abstraction can lower the flows of both rivers and wetlands as their
discharge is derived from both surface runoff and groundwater stores. Rivers draining areas consisting entirely
of permeable rock obtain a large majority of their water from aquifers. For example, the flow of the Colorado
IB Geography Freshwater | Issues and Conflicts
17