SALINITY
STUDY GUIDE
Supporting Stage 5 & 6 Geography
Table of Contents
1.
Important stuff
Page 2
2.
Extent of problem
Page 3
3.
What is salinity?
Page 4
4a.
Sources of salt
Page 5
4b.
Impacts
Page 6
5.
Water Cycle
Page 8
6.
Recharge and discharge
Page 9
7.
Catchments
Page 10
8.
Sub-catchments
Page 11
8a.
Case study : Livingstone Creek
Page 13
9.
Causes: natural
Page 15
10a.
Causes: farming
Page 16
10b.
Causes: urban
Page 16
11.
Management: Preparing for a field investigation
Page 17
12.
Measuring salinity
Page 18
13.
Investigation: water tables
Page 19
14.
Piezometers
Page 21
15.
Salinity indicators: plants
Page 22
16.
Salinity indicators: landscape
Page 24
17.
Salinity indicators: urban
Page 25
18.
Salinity classification
Page 26
19.
Investigation: how bad is salinity at this site?
Page 28
20.
Investigation: where does salinity occur in Wagga Wagga?
Page 30
21.
Research Resources and Internet links
Page 32
Page | 1
1. Important Stuff
Water Cycle
The height of the water table is a balance between inputs and outputs of water to the
groundwater.
1. Dryland salinity
Occurs in dryland farming areas (non irrigated farming). The land has been cleared
of many trees and outputs of water via transpiration from trees decreases so the
water table rises.
2. Irrigation salinity
Occurs in irrigation farming areas. Inputs of water increase from irrigation and the
water table rises.
3. Urban salinity
Occurs in towns. Inputs of water increase from watering gardens, playing fields and
parks and leaky water pipes.
4. Natural risks
Some areas have naturally high water tables and are saline and have been since
recorded history. This can be caused by natural features such as catchment shape,
changes in soil permeability down a hill or extended periods of higher than normal
rainfall.
Page | 2
2. Extent of the problem
"Every day, another chunk of land about the size of a football field is quietly drowning
in salt. By the time a baby born today reaches the age of about 30, a total area
almost equivalent in size to the State of Victoria will have gone under: dead, useless,
ugly, awkward, embarrassing and depressing." Michael Archer and Bob Beale,
Going Native, 2004 (Figures quoted are current best estimate.)
Salinity is a big problem
in Australia. The map is a
forecast of areas with
salinity by the year 2050.
Map: Commonwealth of
Australia, 2001, Dryland
salinity in Aust..... Assess.
Some 2.5 million hectares
of rural land are already
affected by salinity, and
there is the potential for
this to increase to 15
million hectares. Much of
this is Australia 's most
productive agricultural
land. The area damaged
by salinity to date
represents about 4.5
percent of present
cultivated land. CSIRO
Salinity is also a world problem. The world map shows countries which are
investigating salinity. There are currently 77 million hectares of salinised land caused
by human activities.
Page | 3
3. What is salinity?
Salinity occurs when salty groundwater is close to or at the surface of the soil. When
the water table is within two meters of the surface it is within the root zone of many
plants. Air pores in the soil act like a sponge and the salty water is drawn up to the
soil surface. This is called capillary rise. Damage to buildings, roads and plants is
usually a combination of salt and waterlogging.
There are different causes of salinity:



dryland salinity;
irrigation salinity; and
urban salinity.
This study is concerned mainly with urban and dryland, not irrigation salinity.
Page | 4
4a. Where does the salt come from?
The salt in groundwater can come from:



rainfall (cyclic salt in the water cycle)
the weathering of rock including old sea sediments
wind blown (Aeolian) salt crystals from oceans and salt lakes
Scientists estimate that 15 kilograms of salt per hectare enter the soil each year in
South Eastern Australia.
If the water table rises, salt crystals in the soil will be dissolved and enter the
groundwater.
Once the salt is dissolved in the groundwater, the salt goes where the groundwater
goes.
Page | 5
4b. Impacts: damage
Is this the future?
Photo: Dept. Conservation, Forests and Lands Vic.brochure "Soil Salting" 1987
buildings
Page | 6
former football field
infrastructure: roads and steel water pipes
dryland salinity: farming
Photos courtesy of:
Department Infrastructure, Planning, Natural resources
Wagga Wagga Projection
Below is the projected cost of the financial impact of salinity if no action is taken over
the next 30 years.
Page | 7
Item
Water infrastructure
House costs
Sewerage pipes
Gas pipes
Agriculture
Parks and sports grounds
Septic tanks
Footpaths
Present value
$87 883 000
$56 198 000
$8 308 000
$5 782 000
$3 586 000
$850 000
$714 000
$66 000
Total
$163 387 000
5. Water cycle: water table movement
The height of the water table changes as the amount of water entering it (inputs) and
leaving it (outputs) changes.
After a period of rainfall, water may enter the groundwater and the height of the
water table rises.
After a dry period, the water table may fall as the groundwater slowly drains down
the catchment. The height of the water table is a balance between inputs and
outputs of water to the groundwater.
Activity: Compare the water table depth under natural conditions to when we have
dryland farming and urban development in the diagram above.
Conditions
Natural Conditions
Dryland Farming
Urban Development
Page | 8
Water Table Depth
6. Recharge and discharge
Soil and rock which allows water to soak in quickly is permeable. In these parts of
the landscape, rainwater can infiltrate down and enter the groundwater. These are
recharge areas.
Discharge areas occur where the water table is at or close to the surface.
In the diagram the movement of groundwater is slowed by a clay barrier. The
groundwater builds up behind it and is forced to the surface, creating a discharge
area.
Page | 9
7. Catchments
Catchments are areas of land which drain water to their lowest parts. There are two
important parts to this definition.
1. An area of land. How we use the land is very important. Trees cleared in
upper catchments can cause water tables to rise lower in the catchment.
2. Drain water to the lowest parts. Water connects the different parts of a
catchment. Water will transport things from upper to lower parts of
catchments. Salt dissolved in groundwater will go where the groundwater
goes.
To solve salinity and other environmental issues we need to manage whole
catchments, not just little parts. One town or one farm upstream can cause problems
for others downstream.
Satellite image: Australian Greenhouse Office
The satellite image above shows a section of the Murrumbidgee catchment with
three of its sub-catchments. Dark green/brown represents areas of remnant
vegetation (natural bushland). Lighter colours, brown/white, indicate cleared farming
areas. There are very few areas of deep rooted, natural bushland left which would
use groundwater through transpiration, causing water tables to rise in lower
catchment areas.
Page | 10
8. Sub-catchment salinity
Over 410 000 tonnes of salt pass Wagga Wagga each year, dissolved in the waters
of the Murrumbidgee River. The Murrumbidgee flows into the Murray River and down
to Adelaide which takes about 30% of it's drinking water from the Murray. At present
the salinity of the Murray near Adelaide is over the 830 EC threshold for desirable
drinking water some of the time and within a few years it is predicted it will be much
worse if nothing is done.
To fix the problem, land managers need to know where the salt is coming from.
Researchers' in the Wagga Wagga area have been testing sub-catchment creeks of
the Murrumbidgee. The worst catchments have been identified, so that land
degradation problems which cause salinity can be targeted and the catchments
managed on an ecologically sustainable basis.
Page | 11
Below are some of their results.
Catchment Murrumbidgee Yass R. Jugiong Muttama Kyeamba
Characteristic
(Wagga
Creek
Creek
Creek
Wagga)
Water salinity
(EC)
100
451
838
858
480
River salt
load (kg/day)
1 126 027
29 851
60 012
19 314
1 977
The salinity of the Murrumbidgee is low (100 EC) but its large volume means the
river transports a lot of salt each day.
Salinity units used are EC's (electrical conductivity).
The Kyeamba sub-catchment within the Murrumbidgee catchment has been divided
into smaller catchments again and the salt content of flowing creeks was measured.
From this we can get an idea of the land areas contributing the most salt to the
creeks. This shows the salt problem is not even across the landscape.
Map courtesy Department Infrastructure, Planning, Natural resources
Page | 12
8b. Catchment case study: Livingstone Creek
An understanding of the movement of salt through a catchment is important so the
best remedial measures are used to fix salinity problems. Most salt movement in a
catchment occurs as dissolved salt in water, scientists need to know how the water
cycle works at a particular place because where the water goes, the salt goes.
The Livingstone Creek sub-catchment covers 7% of the area of the Kyeamba
catchment but contributes up to 70% of the salt load in Kyeamba Creek. A study of
the landform, geology, groundwater and streamflow of the Livingstone subcatchment explains it's salt problem and the best way to fix it.
Page | 13
The hilly, upper catchment has fine grained metamorphosed sedimentary rock
(meta-sediments) which release salt when weathered. A band of hard granite rock
which weathers slowly constricts the middle catchment so all water has to move
through a narrow area.
The lower catchment opens up to flatter, deeper, alluvial (stream) deposits.
The groundwater can move deep into the meta-sediments where it dissolves the salt
from the rock and then forms an underground salty lake. The granite blocks the
movement of groundwater and forces it to the surface into the creek.
Once the salty creek and groundwater have passed the granite it moves into the
alluvium of the lower catchment causing salinity problems there. The salty creek and
groundwater then leave the Livingstone Creek sub-catchment into the main
Kyeamba catchment.
To manage the salinity problems of the lower Livingstone Creek and Kyeamba
catchments, land managers need to fix the problem at the source of the salt in the
meta-sediments in the upper catchment. Measures taken further down will not stop
the continual addition of salt from the meta-sediments.
Note: The 'Big Springs', natural spring water company collects water from the granite
area at the northern end of the catchment. The water cannot penetrate the granite
which has little salt and runs off quickly and so is very fresh with little salt.
“The waters of Big Springs are absorbed by the granite soils of the Flakeney
Ranges and run through aquifer and underground channels that are filtered
naturally through sands and gravels”
http://www.bigspringsriverina.com/history.asp
Page | 14
9. Natural risks
Some areas have naturally high water tables. Human impacts often make natural
problems worse.
Discharge area occurs at change in slope.
Large volume of groundwater from a broad
catchment is "squeezed"
at the catchment mouth.
Page | 15
Groundwater builds up behind
less permeable soil.
Groundwater is forced to go over a bump in the
basement rock. This is a contributing factor to
salinity in some of the large irrigation areas along
the Murray River.
10a. Causes: dryland farming
Clearing deep rooted
bushland and replacing
it with shallow rooted
pasture grasses and
crops has led to more
rainwater making its
way into the
groundwater.
Compare the map of
dryland salinity with the
satellite image showing
the area of native
vegetation cleared in
red.
10b. Causes: urban
Increased inputs into the groundwater:



Watering of gardens and recreational areas such as parks and sporting areas.
Leaking pipes such as water supply pipes.
Rainwater from roofs run into rubble pits in the ground instead of surface
gutters.
Page | 16
11. Management
Sources of groundwater recharge (Wagga Wagga Urban Pilot Study)
Rainfall
22%
Rubble Pits
14%
Leaky water pipes
47%
Leaky sewer pipes
12%
Garden watering
5%
Urban area solutions
Engineering:




Install bores in trouble spots and pump the water out. Wagga Wagga has nine
de-watering bores which automatically pump out groundwater when the water
table is within 2.5 metres of the surface.
Deep drainage. Sub-soil drainage has been installed at the Wagga Wagga
Showground to stop the water table rising to the surface.
Take rainfall runoff from roofs into street gutters instead of putting it into
rubble pits in the ground.
Repair leaky water pipes.
Educational:

Encourage residents to place timers on garden sprinklers and plant
"waterwise" gardens.
Dryland farming solutions




Plant trees and shrubs in
recharge areas. (Trees
pump the groundwater
out and shrubs intersect
soil moisture from rain
before it reaches the
water table.
Replace shallow rooted
pasture grasses with
deep rooted varieties.
Catchment management
as well as farm
management since salinity crosses farm boundaries and is a catchment scale
problem.
Landcare educational programs.
Note: It is not possible to fully treat management in this study guide. The Department
of Infrastructure, Planning and Natural Resources (DIPNR) has an excellent web
site. See 'Links" at the end of this study guide.
Page | 17
12. Measuring salinity

Most meters measure the electrical conductivity of water.

Batteries are connected to two wires (electrodes). Salty water
will conduct electricity between the two electrodes, the saltier
the water, the more electricity is conducted.

The unit of electrical measurement used is Siemens. The
meter we use in the field measures milliSiemens (mS) per
centimetre (the electrodes are one centimetre apart).

Often the literature will use microSiemens (uS) and EC
standing for electrical conductivity. These two units are the
same. To convert milliSiemens to EC's or uS multiply the
reading by 1000. The meter in the diagram shows 1.65 mS
which is 1650 uS or EC's.
Water Salinity Levels for Use
Source/Use
uS/cm or EC
distilled water
0
Source
uS/cm or EC
limit poultry
5 800
Murray R. (mouth)
790
limit beef cattle
16 600
desirable limit people
830
limit adult sheep
23 000
absolute limit people
2 500
Pacific Ocean
58 000
Conversions
deciSiemens per meter (dS/m) = milliSiemens per cm (mS/cm) times by 1000 equals
microSiemens per cm (uS/cm) = Electrical Conductivity units (EC's)
Example 1.5 dS/m = 1.5 mS/cm = 1500 uS/cm = 1500 EC
Care of the meter




Turn the meter off after use.
Only place it in the water 2 cm.
Don't put the electrodes in mud.
If is accidentally dropped in the water please let your teacher know.
Page | 18
13. Investigation: water table changes
Aim
How does the planting of trees impact on the water table in a dryland salinity
discharge area?
Method

Plant 4 000 eucalypts at a spacing of one tree every 3 metres.

Monitor water table changes over several years with a piezometer.

Monitor tree growth and record rainfall.
Results
Salinity area eucalypt plantation 2002
Page | 19
Salinity area eucalypt plantation 2003
Salinity area planted with trees with piezometer in 2004.
Graph and photos courtesy Department Infrastructure, Planning, Natural Resources Wagga Wagga research centre
Discussion

Did the height of the water table change (dynamic) or stay the same (static)
over the study period?

Suggest reasons for the higher water table in winter each year.

Describe what the red lines in the graph represent and explain why they
became steeper over the three years.

Describe what happened to the number of leaves on each tree as they grew
older.

What was the impact of the trees on the height of the water table?
Page | 20
14. Piezometers
Piezometers are holes bored into the ground which give access to the groundwater
so the height of the water table can be measured and samples of groundwater
obtained for testing for salt concentration. The bore holes are lined with plastic pipe
which is protected above ground by a metal casing shown on right.
The graph of the piezometer shows the seasonal water table movement at the
DIPNR Research Centre salinity site from the previous page.
Page | 21
15. Indicators of salinity
Plant indicators
Page | 22
Swampy couch
Sea barley grass
Spike rush
Salt bush
Some plant species can tolerate high salt concentrations and grow in these areas while
others can only live in lower concentrations. Zones or concentric circles of plants can be seen
in some areas indicating a change from high to low salinity.
Succulent plants such as some salt bushes often grow in saline areas. These plants usually
indicate dry conditions but salinity areas have high water tables.
Plants rely on obtaining water through their roots. This depends on water naturally moving by
osmosis from an area of lower salt concentration, usually in the soil, to one of higher salt
concentration, found in plant cells. When the soil water is saltier than the plant cells, the
plants can't obtain water by this method and may die from lack of water.
Page | 23
16 Salinity indicators
Landscape indicators
Dead Trees
Bare patches
Clear Water
Puffy soil with salt crust when dry
Photos courtesy Department Infrastructure, Planning, Natural Resources
 Trees often die from waterlogging, their roots no longer able to breath.
 Bare patches occur where the salt concentration is too high for plants to grow.
 Salt dissolved in pools of water causes the clay particles suspended in the water
to
clump together and sink to the bottom, making the water clear (except for algae).
 A salt crust may be seen when the soil is dry and it may feel "puffy" when trodden on.
Page | 24
17 Salinity indicators
Urban indicators
Steel infrastructure
Salt line on bricks
House water pipes
Breakdown of road surface
Photos courtesy Department Infrastructure, Planning, Natural Resources



White markings on the surface of bricks formed from water evaporating,
leaving salt crystals behind.
Steel in contact with ground rusting more than normal.
Breakdown of road surface caused by the saturation of the underlying soil and
roadbase.
Page | 25
18. Salinity classification
Class 1. Earliest visible signs of salting are when the water table has started to
move salts into the root zone. Soil salinity (1:5 soil/water mix) 2000 to 4000 EC.
Signs to look for:

boggy areas; reduced crop yield; patches of salt tolerant plants such as sea
barley grass and couch.
Class 2. Moderate salting occurs where the water table is at the surface for
extended periods. Highly salt tolerant plants present. Soil salinity 4 000 to 8 000 EC.
Page | 26
Signs to look for:

scattered bare patches (up to 1m2); salt crystals on surface when dry; pools of
water are clear; normal grasses replaced by sea barley grass, couch, beard
grass, plantain and other salt tolerant species.
Class 3. Severely affected areas have extensive scalding (bare areas) areas and the
presence of salt loving plants (halophytes). Soil salinity over 8 000 EC.
Signs to look for:


extensive areas of bare ground with salt crystals when dry; salt loving
succulents; sheet and gully erosion on sloping land.
Soil salinity test: place 1 part soil in 5 parts water and shake to dissolve any salt in
the soil then test solution with salinity meter.
Page | 27
19. Investigation: how bad is salinity at this site?
Use your knowledge to investigate salinity at this site.
Page | 28
Activity:
Aim
Write a report on your investigation using the following headings.
The purpose of your investigation.
Methods
Survey the area for plant and other indicators of salinity by dragging and dropping
the red 1m2 quadrat frame on the site being investigated. Record the species of
plants and other salinity indicators in each quadrat. The white transect line is 30
metres
long.
The survey needs to be carried out in a manner so we have confidence that the data
collected is accurate.



The quadrat needs to be dropped randomly on the survey site.
You need to study enough quadrats to be sure you have surveyed the whole
area. Do five quadrats.
There is a transect line you may wish to use (it is fixed).
Results
Include a table of the data collected.
Quadrat
% bare
% succulents % sea barley
% couch
One
Two
Three
Four
Five
Discussion/conclusion
What did you find out?
How would you improve this investigation?
Is there other data or equipment you would have liked access to?
Page | 29
% doc
20. Investigation: how does water table height vary in Wagga?
Aim
Some residents have commented that their rose gardens and lawns have been
dyeing so Wagga Wagga City Council have contracted you to investigate the water
table height in an area of Wagga Wagga and write a report.
Method
Research existing GIS (Geographic Information Systems) data which has the
location of piezometers and their readings. You now need to analyse your results.
Air photo courtesy Department of Lands
Piezometer
Land surface height (m)
1
2
3
4
5
6
7
8
9
10 11
12
193 195 200 198 200 212 195 210 221 203 216 217
Ave. water table height (m) 0.1 1.0 4.9 11.6 0.1 12.8 1.8 7.9 12.4 5.3 7.0 12.2
Ave. salinity (EC x100)
67=6 700 EC
Page | 30
67 63 63 174 43
37
52 171 77
25 87
35
Results
Look for relationships between location, landform height, water table height and
salinity. Display these in graph form.
Draw a salinity hazard map where water tables are within 2 metres of the surface.
Use the vertical air photo to comment on land use.
Conclusion/discussion
What do the results indicate? How could you improve this investigation? is there any
equipment or additional data that would help?
Page | 31
Research Resources
Why Wagga has salinity
(pdf 218 KB)
Dryland salinity in Wagga
(pdf 118 KB)
Managing salinity in Wagga
(Word 30 KB)
Urban Salinity
(Murrumbidgee CMA Word 23 KB)
Map Wagga salinity bores
(JPEG 86 KB)
Map salinity in Wagga
(JPEG 53 KB)
Dryland Salinity
(193 pages pdf 815 KB)
River Murray, A Salinity Perspective
(CSIRO pdf 190 KB)
Salinity National Action Plan
(pdf 239 KB)
Links
Department of Infrastructure Planning and Natural Resources * highly recommended
(do a salinity search)
www.dipnr.nsw.gov.au
Murray Darling Basin Commission
www.mdbc.gov.au
Land and Water Resources Research and Development Corporation National
Dryland Salinity Program
www.lwrrdc.gov.au/ndsp/
Page | 32