For the most part, it was Penny’s from heaven

CADE Colls at Glenroc Station wasn’t quick enough to empty the rain gauge when the downpour from ex-Cyclone Penny began on the night of 11 January to get an accurate reading.

The gauge was already overflowing “by the bucketful” and, as a result, he measured only 430mm for that 24 hours.

“We will never know for certain, but I reckon it was probably more like half a metre [500mm],” he said.

There is a small argument in the family about whether it’s the biggest rain event at Glenroc in the 47 years they have been custodians of the property.

Mr Colls thinks he has a memory of it being higher, but father Richard is adamant Molongle Creek that runs through Glenroc Station has never been higher than the morning after Penny visited.

While the rain was welcome, it wasn’t all good news.

In the morning, Cade’s brother Bobby Crossland took a four-wheel buggy out along the 1.5km wall of the The Ponds dam fearing it would be near capacity.

He was right and narrowly missed being swept away as the wall broke moments after he drove past that spot.

He was able to drive onto higher ground and capture the breach which basically drained the dam leaving it to revert to the unconnected paragrass ponds for which it was named. Bobby took the video shown here.

The Colls also lost The Golden Mile dam, another water storage on the property about the same size at The Ponds.

Mr Colls said he had been able to get a digger to the site to repair some of the damage getting it ready to bring in a scraper when it was dry enough to restore the dam wall properly.

The rain event tested the LDC’s community water monitoring and automated water sampling systems.

LDC Monitoring and Evaluation Officer Barb Colls said there were 106 bottles collected for analysis from water flows immediately after the downpour at several sites across the BBB catchment.

Analysis of the samples provides data that will give everybody involved in the project – from scientist to grazier – a picture of the effectiveness of the gully treatment methods so far employed.

“It provides valuable information to the source catchment model as well as contributing to important research on sediment and nutrient loads in water flows within the BBB,” she said.

The rain resulted in some flooding in the Burdekin River and was patchy throughout the BBB catchment, but some falls were very intense.

Strathbogie Station reported about 400mm of rain in just eight hours.

Bogie River: Strathbogie 432 mm (+27mm after 9am); Eton Vale alert 224 mm; Eton Vale 98mm; Mt Pleasant 82mm.

Rainfall in catchment area below the Burdekin Falls Dam: BFD Hydro site 153 mm; Myuna 84mm; Dalbeg 121 mm; Expedition Pass Ck 56mm (+35mm after 9am); Millaroo 37mm; Landers Ck 79mm (+14mm after 9am).

(Map supplied by Zoe Bainbridge)

A rainfall map of part of the BBB using data from the LDC and BOM weather stations

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KEQ #1

Figure 1. Total fine sediment reduction by project type and erosion source. Inset shows the proportion of the total project area for each project type.

These estimates have been calculated using two methods: 

1) The pollutant reduction component of the Alluvium/Great Barrier Reef Foundation (GBRF) investment tool for hillslope and streambank erosion management projects; 

2) The Reef Trust Gully Toolbox method for gully erosion management projects. The LDC Water Quality Report 2020 (Waterhouse et al., 2020) highlights that a number of assumptions underlay these calculations, therefore these figures should be treated as the best available estimate of sediment reductions to date.

Preventing sediment from reaching the Great Barrier Reef

Each wet season sediment is washed into local waterways and out to the Great Barrier Reef (GBR). 

Most sediment is very fine, and can stay suspended for a long time and can travel great distances. Valuable topsoil is lost from production, and increased concentrations on the reef can be harmful to seagrasses and corals. 

Landholders in the BBB have completed 69 on-ground water quality practice changes, and it is estimated that these have contributed a fine sediment reduction of 6,154 tonnes per year from reaching the GBR. 

Of this, approximately half of the sediment savings are attributable to grazing land management changes on hillslopes and streambanks, and the other half as a result of gully remediation treatments across a broad range of scales, as shown in the graphs above. 

The table below also highlights the relatively small area of intervention in the gully management projects compared to the large sediment savings that these can achieve - 60 per cent of the sediment savings over only 4 per cent of the project area.

Table 1. Estimated sediment reductions (tonnes) from projects completed in the LDC Project to date.

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*GLMWW = Grazing Land Management Wire and Water

KEQ #3

*The Exploring New Incentives activity area has provided an opportunity for graziers to adopt improved land management practices through a range of activities. For some of these properties, it was the first time they signed contracts for on-ground works.

KEQ #4

The LDC project monitors four gully sites (represented in this table) with gold standard equipment and analysis, carried out by CSIRO.

Results have been compiled in a preliminary report from Bartley et al (2020), with the final report expected to be released by the end of 2020. The preliminary report shows all four sites have indicators of improvements, notably the Strathbogie and Mt Wickham sites.

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Reef regulations - grazing, standard conditions

  1. For land in good or fair condition (more than 50 per cent ground cover at 30 September), continue using measures to maintain land condition.
  2. For land in poor condition (less than 50 per cent ground cover at 30 September), steps must be taken to improve land condition.
  3. For land in degraded condition (less than 20 per cent ground cover at 30 September), steps must be taken to improve land condition OR prevent areas from further degrading or expanding.
  4. Keep records of measures taken and also of agricultural chemicals, fertiliser and mill mud or mill ash applied to land.
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