catchment modelling , rather than providing an indication of water quality progress in the catchment . In addition to the community water quality monitoring results described below , it does provide useful context when the monitored loads are assessed for the LDC Project on completion .
Nine river and creek sites across the BBB catchment are being sampled by landholders during rainfallgenerated high flow events of the 2018-19 , 2019-20 and 2020-21 wet seasons . Sub-catchment sediment and nutrient concentration data collected will be used to improve the modelling of the BBB catchments as part of the Paddock to Reef program ( Source Catchments model ). The data provides a validation check against modelled concentrations for these same river and creek locations and will also act as a baseline dataset to examine trends over time . The identification of higher sediment and nutrient contributing sub-catchments can then be coupled with broader landscape understanding including slope , soil types , associated erosion processes and other factors for refined catchment characterisation and prioritisation .
Whilst the Burdekin catchment had an average-sized water year as noted above , within the BBB catchment area , below average to average rainfall occurred . Rainfall totals for the 2020-21 wet season ranged from 370 mm at Gatton Vale to 1630 mm at Mt William ( Dalrymple Heights ). For the 2020-21 water year , the Bowen River at Myuna flow gauge has recorded ~ 217,000 ML , well below its long-term annual average of 877,000 ML ( based on a 60-year flow record ; © The State of Queensland 2021 ).
There were 16 water samples collected this wet season due the lower river flow , with Samplers reporting lower intensity and patchy falls . Depending where the rain fell , one to two flow events were sampled by landholders at five of our sampling sites :
• Christmas 2020 flows : Pelican Ck , Rosella Ck
• Jan 2021 flows : Little Bowen ( Junction ), Rosella Ck
• March 2021 flows : Broken R , Little Bowen ( Junction ), Pelican Ck and Bogie R .
Samples were analysed for suspended sediment ( Figure 6 , Figure 7 ), particulate nitrogen ( Figure 8 ) and particulate phosphorus ( Figure 9 ) concentrations . Combined with the previous wet seasons , a total of 163 samples have now been collected under this project .
Key results : Suspended sediments
Where landholders were able to sample in the 2020-21 wet season , the additional data provides greater confidence in the average concentrations for those sampled sites . When all data points are combined across the three wet seasons , average suspended sediment ( SS ) concentrations for each of the sampled BBB river and creek sites show large variation across the catchment ( seeFigure 6 ). These differences reflect landscapescale processes of the entire upstream catchment area . Higher SS and nutrient concentrations often relate to highly erodible soil types , the underlying geologies , and areas of steep slopes , but are also linked to rainfall patterns .
Figure 7 shows further detail of the variability between sites . All samples collected at each site over the three wet seasons were pooled to determine an average site concentration . Over the three sampled wet seasons site averages ranged from 20 mg / L ( Broken River ) to > 4,800 mg / L across sites in the Little Bowen sub-catchment ( these sites also had the greatest range in SS concentrations ). The 2020-21 wet season sediment concentration data increased the site averages for the Little Bowen River ( Junction ), Pelican and Rosella Creek sites .
Only one small flow event occurred in the Broken River sub-catchment this wet season , with all four samples measuring < 15 mg / L . The significantly lower site average ( 20 mg / L ) has remained consistent across the three
45