• The annual average modelled PP reduction for the LDC Project is estimated at 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 estimated at 3,230 kg / per year . On average the LDC Project contributed 26 % of the Burdekin basin PN load reductions .
The results for Q3 were reported using both the Alluvium tool ( also reported in Q1 ) and the Source Catchments model ( also reported in Q2 ). Use the Alluvium tool the greatest total reduction of 6,102 tonnes was estimated in the Bowen sub-catchment , which accounts for 58 % of the total fine sediment reduction estimated for the BBB catchment . All other sub-catchments contributed 15 % or less of the total BBB fine sediment reduction . Similar patterns in the relative sub-catchment contributions were found for fine sediment , PP and PN using the Source Catchments model .
For this report , it was possible to calculate a relative estimate of the sub-catchment scale reductions using two methods :
1 . By summing the project-specific estimates ( using the Alluvium tool ) presented above . 2 . Source Catchment model estimates .
As highlighted above , the Alluvium tool provides a relatively simple assessment which is useful to consider differences between project outputs . Both methods start with the project data supplied by the LDC Project team and reviewed by the P2R Management Practice Adoption Team in DAF . A major difference between the two modelling approaches is in accounting for sediment reductions associated with gully management improvements . The Alluvium tool assumes sediment reductions for reported improvements in gully management practices , whereas the Source Catchments model requires point source estimations of gully sediment reductions reported via the Reef Trust Gully / Streambank Toolbox . The results for these two methods are expected to be different as the approaches apply different methods and assumptions . In particular :
• The efficacy of some practices is applied differently between the Source Catchments model and the Alluvium tool ( e . g ., whoa buoys ) and different assumptions are applied regarding the project effectiveness and in some cases , project area . Project area has a dominant influence on the results in the Alluvium tool because it applies the efficacy over the full project area provided which may be unlikely for some practices .
• The Source Catchments model provides a better representation of system processes and fine sediment dynamics .
• The Alluvium tool draws on the 2016 Source Catchments model dataset which has since been updated ; an updated baseline model is now used in the Source Catchments model output which would account for differences between the results .
Using the Alluvium tools allows the presentation of results for individual years at the sub-catchment scale , as shown in Table 8 and Figure 7 . The contribution from the sub-catchments ranges between years , with no clear pattern . Note that the first project completions were in 2019 . The greatest total reduction of 6,102 tonnes was estimated in the Bowen sub-catchment , which accounts for 58 % of the total fine sediment reduction estimated for the BBB catchment .
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