area of the project as supplied by the LDC Project team to determine the area over which improved practice is undertaken . The process applied the following steps :
• Alluvium were provided with a spreadsheet of the project-specific data indicating the project location , project area , sub catchment , practice at the beginning of the project and practice at the end of the project ( assessed by the DAF P2R Management Practice Adoption Team ). More specifically , project level data is collected as follows :
- LDC Project field officers map out ( using ArcGIS ) the project area polygons ( usually paddock scale ) and the planned practice change e . g ., fencing or watering point modification etc .
- Landholders and LDC Project field staff complete the P2R practice change “ before ” project questions and once acquitted , the “ after ” project questions ( aligned to the P2R Grazing Water Quality Risk Framework ). Land Condition Assessment Tool ( LCAT ) assessments were introduced in 2020 and completed by LDC Project field officers .
- The P2R Management Practice Adoption in DAF team assess the responses to the P2R questions ( before and after ) to define the potential step change in water quality risk ( rated A-B-C-D ).
• Practice change is noted as being either attributed to hillslope practice or improvements to gully management . Hillslope practice changes typically related to projects associated with changes in watering points ( offstream watering ) and / or fencing of areas to manage stock pressures . Gully improvements included reprofiling , earth banks , road management , gully head remediation , soil amelioration , seeding and fencing , plug dams and headcut stabilisations ( varying on a project by project basis )
• Where a project may address both , then it is assumed that the full amount of practice improvement is applied .
• Where a project only focuses on one component , then half of the amount of practice improvement is applied . There is limited information to enable disaggregation of the amount of likely improvement possible from improved practice or gully management . It is likely that improved land management will lead to better ground cover and reduced gully development , so reductions were assumed on an equal basis .
• Where the project ’ s practice change assessment indicated a whole step change improvement in grade ( e . g ., D to C – or very high to high risk ) applied over the project ( assessed using the P2R WQ Risk Assessment framework ), the following efficacies were applied ( derived from Silburn et al . 2021 ): ):
- Efficacy for D to C hillslope cover or gully prevention = 76 %
- Efficacy for C to B hillslope cover or gully prevention = 61 %
- Efficacy for B to A hillslope cover or gully prevention = 46 %.
• The calculation was applied on an area ratio basis to scale the loads for a particular practice change . For example , if the project covered 5ha out of a 500ha sub catchment and the practice improvement was from D to C , then a total reduction of 5 / 500 x 76 % x D class sediment load for the sub catchment , was attributed as the fine sediment load reduced by the project .
• Streambank improvements were calculated ( where applicable ) based on an assumed 60 % reduction of streambank load for the area of project compared to the total area of grazing in the sub catchment under a particular practice class , using the same method as described above . This was based on the performance of a number of streambank projects assessed as part of the Investment Pathways reporting for GBRF ( Alluvium , 2019 ).
Gully erosion management projects : The estimates for sediment reduction from gully projects are calculated using the Reef Trust Gully Toolbox ( Wilkinson et al ., 2019 ). Baseline fine sediment yields were calculated using :
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