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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 Unpublished report.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, Hocking et al. Pty Ltd Page ii 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: 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; 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. Hocking et al. Pty Ltd Page iii 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. Hocking et al. Pty Ltd Page iv