( A ) ( B ) ( C )
( D ) ( E ) ( F )
Figure 22 : Glen Bowen water quality monitoring station set up ( A , D ). The instrumentation setup is the same at both treatment and control sites ( B ) the control site sensor cluster on the bed of the gully and ( C ) the control site sensors during an event that was just above the event threshold for sample collection . ( E ) The treatment gully sensor during an event on 7 January 2021 and ( F ) an event at the control site on the same date in Jan 2021 .
Unlike the Mt Wickham site , no ‘ before ’ treatment water quality samples were collected prior to the rehabilitation treatment at Glen Bowen . ~ 600mm rainfall was recorded ( compared to ~ 370 mm in 2019-20 ) at the treatment site and ~ 630 mm at the control site in the 2020-21 wet season , marginally lower than the long-term average for this area .
As a result of the low rainfall in 2019-20 and the impact of the rehabilitation works , no water quality samples were collected at the treatment gully in 2019-20 . There were ~ 17 samples collected at the Glen Bowen control gully during 2019-20 wet season , however , there was insufficient rainfall and runoff to completely submerge the velocity sensors enough for measurement and therefore no discharge or loads calculations were possible at this site in 2019-20 . The treatment site , which has a large catchment area , should have had the same amount or more runoff than the control site . However , other than very small flow ( Figure 22F ), no runoff data or samples were collected from the treatment site .
In the 2020-21 wet season , only four water quality samples were collected during two events ( Figure 23 ). The median TSS value at the Glen Bowen control site was ~ 61,000 mg / L ( compared to ~ 53,000 mg / L in 2019-20 ). This was highest median sediment concentration of any of the study sites ( Figure 17 ). The median Total Nitrogen ( TN ) concentration in 2020-21 was ~ 46,000 ug / L which is much higher than the TN concentrations measured at the site in 2019-20 (~ 8,060 ug / l ) and much higher than all other locations ( Figure 17B ). It is uncertain what the cause of the large increase in TN is for this site . The samples were collected within 72 hours for laboratory processing , and other than a potential input source from the remediation of the neighbouring gully , the reason is unclear . Additional data collected from this site in subsequent years may help explain the extreme differences observed .
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