Modelled estimates of pollutant load reductions play an important role in assessing the impact of the actions undertaken in the LDC Project . The primary platform for catchment scale modelling in the GBR catchments is the Source Catchments model through the P2R Program . The modelled results for the whole Burdekin basin have been calculated for the period through to the end of June 2021 , and Report Card modelling for the full LDC Project period is still underway .
The cumulative modelled fine sediment reduction for the Burdekin basin for the combined LDC Years 1 to 3 ( 2017 / 2018 , 2019 and 2020 Report Card years ) is 29,300 tonnes . Importantly , this includes all investments reported in the Burdekin basin , including the LDC Project . The last reported progress towards the regional end of catchment target was 66.8 %.
An assessment to determine the LDC Project only reduction contributions to the Burdekin basin found :
• The annual average modelled fine sediment reduction for the LDC Project is 2,410 tonnes per year . On average , the LDC Project contributed 44 % of the Burdekin basin fine sediment load reductions .
• The annual average modelled PP reduction for the LDC Project is 2,220 kg / per year . On average , the LDC Project contributed 29 % of the Burdekin basin PP load reductions .
• The annual average modelled PN reduction for the LDC Project is 3,230 kg / per year . On average , the LDC Project contributed 26 % of the Burdekin basin PN load reductions .
As described in Section 3.1 , catchment modelling forms an important part of the LDC Project monitoring and evaluation . The LDC Project has support from the P2R program catchment modelling team to improve the modelling in the BBB catchment based on the additional data being collected . The following tasks have been completed :
• The team assessed the LDC Community Water Quality Monitoring project data and other historical monitoring that has occurred in the BBB catchment to determine sediment and nutrient event mean concentration ( EMC ) data for representative sub-catchments across the BBB . Prior to this project , limited water quality data had been collected during high flows across the BBB creeks and rivers , except for the long-running Bowen River at Myuna flow gauge site ( active since 2003 ).
• Comparison of these preliminary EMCs to those generated by the Source Catchment model suggest that the model is likely over and under predicting sediment contributions from key sub-catchments within the BBB . Additional monitoring data , ideally collected during average to above average wet season flow events ( i . e ., at least a 1 in 5 return interval ) is required to improve confidence in monitored EMC data and to allow for more certain modifications to the existing model . Nonetheless tools , techniques and a framework have been developed to assimilate limited datasets into the model ( Appendix 2 ). Such model refinements reduce uncertainties in model outputs and allow targeting at finer spatial and temporal scales . This in turn would improve investment efficacy in reaching the associated sediment and nutrient targets .
• Collation of sediment particle size data for the Bowen River Myuna gauge and comparison with Burdekin end of catchment data reduced the uncertainty in the GBR Catchment Loads Monitoring
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