This technical bulletin details the

results of salt mapping activities

undertaken between 2005 and

2009. The objective was to address

deficiencies in the completeness and

accuracy of available information on

saline surfaces.

The goals of the project were to:

measure the extent and distribution •

of saline surfaces in the Mallee, not

suitable for agriculture and support a

limited range of native vegetation: and

classify these saline surfaces as either •

naturally occurring or induced so the

MAPPING AND CLASSIFYING SALINE SURFACES IN THE MALLEE REGION OF VICTORIA

role of land use change on salinity

expansion in area and location can be

determined.

What are saline surfaces: are they

more than just salt pans?

Saline surfaces occur where high salt

concentrations in the top soils restrict or

exclude most types of native vegetation

and prevent viable agricultural production.

Saline surfaces are widely distributed

across the Mallee and have increased

since large tracts of native vegetation

At a glance

A method to map saline surfaces, •

and to classify them into salinity

type, was developed and

implemented using remotely

sensed spatial data, GPS survey

and field assessments.

3.8% (142,206 ha) of the Mallee •

currently has saline (surface)

soils.

39% (55,460 ha) of these saline •

surfaces were induced by land

use change.

Figure 1: Induced saline surface soil in former fresh water depression. Photo: Vincent Grinter.

Technical Bulletin # 10

were cleared for agriculture during the

twentieth century.

There are two basic classifications of

saline surfaces:

Natural saline surfaces occur due to •

hydro-geological processes that existed

before European settlement (Figure 2);

Induced saline surfaces occur as a •

result of changed soil water balance

due to land use change following

clearing of native vegetation (Figure 3).

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T e c h n i c a l B u l l e t i n

What is known about their location

and extent?

Estimates of the extent of saline

surfaces in the Mallee have been made

by a number of studies with the most

comprehensive published by Rowan

(1971), based on aerial photos taken a

decade earlier and some ground surveys.

This study presented the best available

estimates of saline surfaces across

the Mallee at that time but included

assumptions extrapolating the limited

data available.

Why was it important to map and

classify saline surfaces?

Information on saline surfaces assists in

land use planning by:

Identifying areas unsuitable for •

agricultural, residential or industrial

development due to their proximity to

saline surfaces.

Providing a benchmark from which to •

measure change in saline surfaces over

time.

Differentiating natural and induced •

salinity to identify where saline

surfaces formed as a result of land use

change and what land uses may be

associated with induced salinity.

Identifying areas that may be •

threatened by further expansion in

saline surfaces.

Methodology

A ground based survey of saline surfaces

across the entire Mallee is prohibitively

expensive (at present), logistically

challenging for more remote areas and

invasive of private land. Further, it would

not provide the information required to

confidently classify all saline surfaces.

A cost effective method was developed

using available spatial data, including

remotely sensed datasets covering the

Mallee, integrated with GPS mapping at

field sites across the region.

The steps undertaken and datasets used:

Field sites were chosen to collect •

visual and spatial information on

saline surface boundaries and a field

assessment of attributes that assisted

in their classification as either natural or

induced.

Field assessment information was •

used to inform a computer model that

integrates satellite and aerial imagery,

and topographic data across the Mallee

region to identify and classify saline

surfaces.

Ground truthing, including the use •

of local knowledge of farmers and

experts, was used to validate the

computer generated results and assign

confidence limits to the result.

The extent and location of saline surfaces

could be accurately mapped using the

methodology outlined above. However,

delineating boundaries between natural

and induced saline surfaces required

further refinement.

Often a saline surface that occurred

due to natural processes has expanded

over time due to land use change. Visual

interpretation at one point in time could

not clearly define boundaries between

natural and induced.

Figure 2: Natural saline surface in bed of salt lake. Photo: Vincent Grinter.

Figure 3: Saline surface induced by clearing. Photo: Vincent Grinter.

Additionally, a characteristic of naturally

occurring saline surfaces is their

consistently high and uniform water

content compared with induced saline

surfaces, which tend to have greater

variability in water content.

Subsequently, a time series analysis of

satellite images was conducted, assigning

a wetness index to saline surfaces over

a range of wet and dry years between

1989 and 2005. Comparing variations

in the wetness index, with adjustments

made for the land systems they occur

on, provided higher resolution to the

classification of natural and induced saline

surfaces.

What was discovered by mapping and

classifying saline surfaces?

The key findings of this project are:

142,206 ha of saline surfaces were 1.

mapped across 3.7 million hectares of

the Victorian Mallee. This equates to

3.8 % of total surface area.

39% (55,460 ha) of total saline 2.

surfaces were classified as induced

and associated with land use change,

particularly clearing native vegetation

over the last 100 years.

Large tracts of native vegetation had 3.

less extensive saline surfaces (2.03%

mapped in 0.87 m ha). Parks and

reserves were where saline surfaces

were largely natural.

Saline surfaces were more frequent 4.

where most land was cleared (4.43%

in 2.82 m ha), where there exists a

combination of both natural and induced

saline surfaces.

Expansion of saline surfaces over the 5.

past 100 years was induced by changing

land use.

This first comprehensive mapping and

classification of saline surfaces does not

provide information on whether expansion

is still continuing or the current rate of

change of saline surfaces. This can be

determined by comparing the current

map (below) with another map in the near

future (for example in 5 - 10 years).

A map of the location and classification of

saline surfaces in the Mallee is presented

in Figure 4. More extensive areas can be

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Mallee Classified Saline Surfaces

Induced

Natural

Figure 4. The location and classification of saline surfaces mapped in the Mallee in 2009.

clearly seen on the map but many smaller

sites appear as a dot or are less than the

pixel size required to appear on a map

at this scale. The map was produced

from the GIS database of saline surfaces,

which was developed by this project

and is available from the Mallee CMA on

request.

The database facilitates production of

more detailed maps where information

is required for any section of the Mallee.

The database also provides quantitative

data on all saline surfaces and enables

further analysis of factors correlated with

salinity either now or in the future.

Conclusions

Field work and spatial data studies over

the past three years have produced:

The first comprehensive map of the •

extent, location and classification of

saline surfaces in the Mallee.

A baseline for measuring and reporting •

future change in saline surfaces.

A methodology to accurately map •

and classify saline surfaces and which

can be used in the future to measure

Project Partners

Published October 2009

This publication may be of assistance to you but the Mallee Catchment Management Authority refers readers to our Terms and Conditions, available from our website.

Printed on recycled Australian paper, made from pre- and post-consumer waste.

temporal change in the extent and

location of saline surfaces.

A spatial database of saline surfaces •

that facilitates relationships (for example

with farming practices and climate

change predictions), leading to more

informed decisions on future land use.

Recommendations

The map and database on current saline •

surfaces is disseminated to assist

decisions on land use and land use

change.

A revised map and database of saline •

surfaces is produced in 5-10 years

and compared with the current map

to determine rate and distribution of

change in saline surfaces.

Disaggregated Land System units •

for the Mallee (when available) are

incorporated in the methodology for

mapping saline surfaces to improve

accuracy and significance for land

management.

Acknowledgements

This work was supported by the Australian

Government’s Caring for Our Country

initiative and Victorian Government

funding.

The MCMA Hydrological Expert Panel is

thanked for their technical contribution.

Landcare coordinators, farmers and

regional staff are thanked for the time

and local expertise provided in selecting

and interpreting field sites and validating

results.

The project was delivered by Agriculture

Victoria Services via the Department of

Primary Industries, Walpeup; through

funding from the Australian Government’s

Caring for Our Country and the Victorian

Government.

References

Rowan, J (1971) “Salting on dryland

farms in north-western Victoria”. Soil

Conservation Authority (Victoria),

Melbourne.

For further information

The information for this bulletin has been

taken from “Mapping the Mallee’s Saline

Land – Stage 3: Classifying Mapped

Salinity”, a report for the Mallee CMA by

DPI, Walpeup.

A copy of the report can be downloaded

from the Mallee CMA website:

www.malleecma.vic.gov.au

For more details contact:

Project Manager - Land, Mallee CMA,

Sarah Whitfield on 03 5051 4377.

Spatial Scientist, Grinter Consulting,

Vincent Grinter on 0400 165 162.

Figure 5. Natural saline basin. Photo: Vincent Grinter.