KEQ : To what extent have major gullies been remediated ?
Water quality instrumentation has been established on five gully sites : Mt Wickham , Strathbogie , Glen Bowen , Mt Pleasant and Havilah . The water quality results , reported by CSIRO along with other data from NESP Project 5.9 and summarised in this report are presented in Section 4.3 . The results highlight that there have been significant improvements in several key indicators at two of the remediated sites , in particular at the Mt Wickham large scale gully remediation site which has shown significant improvements in land condition , vegetation cover and sediment loads as well as comparative concentrations between treatment and control sites .
Additional detail of the progress of the gully remediation projects is provided in Section 4.3 .
Project cost-effectiveness was assessed using a consistent approach developed by the LDC Project (‘ LDC Cost Effectiveness Tool ’) ( see Section 4.2.1 and 5.2 ). This tool takes into account on ground funded costs , landholder costs ( cash and in kind ) and maintenance costs . The effectiveness is captured as the modelled reduction in fine sediment loads following the P2R streambank and gully toolbox process . The intent of this tool has been to allow different types of projects to be assessed for cost effectiveness comparative to each other . The key results are summarised below , excluding a number of data outliers as described in Section 4.2.1 :
• The cost-effectiveness of the grazing land management projects ranged from $ 2.20 / tonne of fine sediment saved ( a grader project ) to $ 223 / tonne ( GLM Wire and Water project ), with an overall average of $ 27 / tonne . Grader projects were consistently the most cost-effective , with 22 ( out of 25 ) of these projects reporting a cost-effectiveness estimate less than $ 40 / tonne of fine sediment saved , and 10 being estimated at less than $ 10 / tonne . Whilst these are among the most cost-effective projects , the sediment savings for each ( particularly per unit area ) are lower on average than other on ground projects , and are unlikely to produce sufficient sediment reductions to reach the water quality targets in the relatively short time frame required ( i . e . less than 5 years ). Thus a mix of options will continue to be explored further into the future , taking into account the scale of implementation . These results of costeffectiveness are similar to those reported for comparable activities in other GBR programs ( Sediment reduction in grazing have ranges from $ 60 / tonne to $ 2,230 / tonne ) ( Alluvium , 2019 ).
• The cost-effectiveness of the 19 completed gully remediation project sites ( all scales ) ranged from $ 8.10 / tonne of fine sediment saved to $ 370 / tonne of fine sediment saved . The average for these sites was $ 120 / tonne of fine sediment . The cost-effectiveness of 7 gully projects was less than $ 50 / tonne , and more than two thirds were less than $ 130 / tonne . The cost-effectiveness of the streambank and revegetation projects was comparable to some of the gully projects . These results of cost-effectiveness are similar to the ranges reported for comparable activities in other Reef programs .
Progress updates for additional activities relevant to the water quality outcomes for the LDC Project are also reported , including the Landscape Remediation Prioritisation Project and roads and drains water quality monitoring are presented in Section 5 .
Refined gully mapping was a major component of the Landscape Remediation Prioritisation Project . A total of 22,311 active gullies were mapped within the study area (~ 3,500 km 2 ), which have a cumulative active area ( currently eroding ) of 4,620 ha . Gullies are not equally distributed through the BBB catchment . There are obvious hotspots which are clear in certain landscape units and key soil types ( outlined further in full report ). Fine sediment estimates from the mapping also highlighted the relative contribution from hillslope and alluvial gullies appeared to be roughly equal , however there were more hillslope gullies ( 12,293 ) than alluvial gullies ( 10,018 ). The specific yield was higher for alluvial gullies .
The sediment yield from individual gullies was highly skewed with a small number of large active alluvial gully systems contributing a disproportionate amount of the fine sediment load . The estimates showed that :
• 1 % of all gullies (~ 260 gullies ) contributed 10 % of the total fine sediment yield .
• 2 % (~ 460 gullies ) contributed 15 % of the total fine sediment yield .
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