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Tasmania NAP region
Landscape Assessment
to Inform Salinity
Management Planning
- For better understanding of salinity causing
processes throughout the Tasmanian NAP region
July 2009
Document history and status
Document status
Date issued
Reviewed by
Revision type
Work in progress
DRAFT
23rd June 2009
24th July 2009
Clarity editing
Adrian James – NRM
North
Formatting review
Project review
FINAL
31st July 2009
A copy of the full report (42MB) is available upon request from NRM North
Please cite this report as:
Hocking et al. (2009). Landscape Assessment to Inform Salinity Management
Planning in Tasmanian NAP region. National Action Plan for Salinity and
Water Quality, NRM North Tasmania. Unpublished report.
This project attracted funding from the Australian and State Government under the
National Action Plan for Salinity and Water Quality (NAP) program.
Hocking et al. Pty Ltd (nor its employees or contractors) does not accept
responsibility for any loss or damage which may result to any person arising from
reliance on all or any part of this information, whether or not that loss or damage has
resulted from negligence or any other cause.
Landscape Assessment to Inform Salinity Management Planning in Tasmanian NAP region
Executive summary
A key question asked by regional planners, land managers and advises is:
Are there external groundwater and salinity processes operating at larger
scales than at the paddock/property scale that overwhelm any mitigating
actions taken individually by farmers?
This work aimed to support SMP process and salinity management planners within
the Tasmania National Action Plan for salinity and water quality (NAP) region and
priority catchments.
The key objectives of the project were to:
 understand salinity causing processes in the NAP region, with an emphasis on
the Clyde, Ouse and Macquarie catchments
 improve the understanding of the impact of current and future climate, land
use and vegetative cover at the catchment and property scale
 identify areas within the NAP region which have the greatest salinity impact.
The project investigated a number of landscapes using a variety of assessment
techniques in order to make judgement and prediction on local and broad regional
catchment issues relevant to the waterbalance and specifically land salinity
occurrence.
Four landscape transects containing salinity were investigated in detail. EM31
horizontal dipole survey data provided the best accuracy for identifying vegetation
indicator land salinity and appears to be a feasible tool for mapping land salinity
hazard. Groundwater drilling of forty (40) monitoring bores identified the cause of
land salinity at each site varied from local dam leakage issues to a broader scale
shallow regional watertable. Shallow groundwater levels (less than 1.0 – 1.5 metres)
were the cause of land salinity at all sites. Seventeen (17) automatic data loggers
were installed at selected bores to monitor groundwater level changes in detail over
time.
Forty Best Practise Salinity Management Planning (BPSMP) properties were mapped
for land salinity using vegetation indicator species. Mapping identified 521 hectares
of land salinity and at least double the area (e.g. approximately 1 560 hectares) as
being marginally salt effected.
Transect modelling (e.g. two dimensional flow) suggests agronomic methods have
limited likelihood to completely rehabilitate land salinity at most sites. At two sites,
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Landscape Assessment to Inform Salinity Management Planning in Tasmanian NAP region
conversion of the entire transects from current landuse to perennial grass species and
trees had minimal impact on the shallow watertable area.
Four detailed groundwater models were constructed across the NAP region, they
were: Flinders Island, northern catchment, southern catchment and Ouse Catchment.
Groundwater model calibration results were considered good with an overall scale
root mean square of 3.04% and a convergence criteria of <0.05 metres, which fits
well within recommendations as part of Australian groundwater modelling
guidelines.
Four landuse change scenarios were considered in the NAP region, annual results
suggest:
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revegetation of agricultural land to native vegetation would reduce groundwater
baseflow by 7 GL and shallow watertable area (e.g. <1.5 metres) by 117 700
hectares
tree decline will cause an increase of shallow watertable area (<1.0 metres) by
33 600 hectares and 16 GL of baseflow to waterways
climate change scenario results show variable results across the region, where a
decrease in shallow watertable area by 38 000 hectares and 20 GL of
groundwater baseflow
irrigation expansion was considered in the midlands. Simulations suggest a net
increase of groundwater baseflow by 8 GL and shallow watertable area by
17 500 hectares.
Implications from the various landuse change scenarios suggest;


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tree decline needs to be addressed at farm and catchment scale via the
comprehensive salinity management plan process to at least stabilise the
effective rate of tree decline in the Midlands
climate change was simulated to increase saline baseflow, the implications of
increased baseflow on surface water quality (salt and nutrient load) may have on
farm and urban water supplies
irrigation development will impact the catchment water balance. Revegetation
in some locations of the region/property may assist in the mitigation of the
negative impacts of irrigation. The impact individual regions and properties
have on land salinity should be further considered.
Some modelling scenarios have a net increase and others have a net decrease in the
catchment waterbalance, the cumulative impact of these scenarios may appear to
have a near zero change in catchment waterbalance. However, at the catchment scale
it is likely there would be significant changes in the waterbalance despite the overall
‘average’ impact may appear negligible. Such maybe the case across a variety of
scales, this must be considered where interrogating landuse change scenarios.
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Landscape Assessment to Inform Salinity Management Planning in Tasmanian NAP region
Figure 1 Areas within NAP region which have greatest salinity impact
The project has identified the areas within the NAP region which have the greatest
salinity impact (Figure 1). In general, these locations are generally located on the
mid and western flanks of the Northern Midlands, however localised variations
occur.
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