1 . The current rate method - the mean annual gully or streambank erosion rate is estimated from the difference in gully volume or streambank position between two recent dates for which historical data is available , such as air photos ( the period must be > 10 years and the estimate may need adjusting to represent average climatic conditions ).
2 . The whole-of-life method - the current gully erosion volume is divided by gully age , and then typically scaled down to account for decay in erosion rate over time . This is used where insufficient historical data are available .
The effectiveness of erosion control is estimated as a proportion of the baseline yield . Delivery to coast is defined for each Management Unit by Paddock to Reef Program catchment modelling .
It was anticipated that the
P2R Program Projector Tool for estimating the water quality outcomes of grazing projects would be available by now , and much sooner in the implementation of the LDC Project . The Alluvium Tool has provided a useful resource as the only source of sediment reduction data throughout the LDC Project .
The cost-effectiveness data was calculated using the LDC Cost Effectiveness tool ( Star et al ., 2019 , see Section 5.2 ), and applied the following assumptions :
• Figures calculated using the LDC Cost Effectiveness Tool and the support of DAF in running each project through the tool ;
• Landholder costs ( cash and in kind ) are included ;
• On ground funded costs are included ;
• Program and activity area costs not yet included ;
• 9.8 % maintenance costs each year are included ;
• 7 % discount rate ;
• Results are NPV ( not annualised );
• Calculated over a 20 year timeframe ; and
• Sediment abatement inputs to the cost effectiveness derived from Gully Toolbox and the pollutant reduction elements of the investment tool developed for Alluvium for the Great Barrier Reef Foundation Reef Trust Partnership ( Alluvium , 2019 ) and all abatements are assumed effective within year 1 for consistency .
Five sites have been instrumented with water quality monitoring equipment to provide measured water quality outcomes at sites with different management interventions and different landscapes . The monitoring has been undertaken by CSIRO in a collaborative project funded by the National Environmental Science Program ( NESP ). The methods include a combination of vegetation , rainfall , runoff , water quality and terrain monitoring and are detailed in Bartley et al . ( 2021 ).
The results of the assessment of fine sediment reductions for each project are shown in Table 3 . Given the ( sometimes large ) assumptions underlying these calculations , these figures are reported as estimates only . Even though there are likely to be some estimates that are more uncertain than others , the results still provide a useful estimate of the likely scale of impact of each project , and the different types of projects , to inform investment decisions for the remainder of the LDC Project .
A comparison between this method and the results from the P2R Projector Tool could be undertaken when this becomes available , as presumably the Projector Tool is likely to be the preferred approach going forward . This was anticipated for the current report but is not available .
Estimated reductions for particulate nutrients are not yet available . However , the results of the LDC Community Water Quality Monitoring Program and the CSIRO study sites indicate that the particulate nitrogen ( PN ) concentrations in the BBB catchment are closely aligned with fine sediment concentrations , and therefore , it can be assumed that the proportional reductions in PN would be similar to that predicted
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