Twelve of the 19 small-scale sites were mapped as being in the‘ Narrow leaved ironbark in deeper soils’ land type. Four of these had soils that were classified as Sodosols due to dispersive properties or soil test results( i. e. % CEC for Sodium > 6). The remainder had slightly less erodible soils such as Chromosols that slaked but didn’ t disperse in water. The remaining seven small-scale gullies were in‘ Loamy alluvials’( two sites),‘ Clayey alluvials’( two sites),‘ Downs country’( two sites) and‘ Box country’( one site). Most of the soils at these seven sites were Sodosols, Vertosols or Chromosols. Table 2 summarises the soil characteristics for each site.
RAINFALL
Rainfall, and the subsequent runoff it produces, is an important environmental factor affecting the success of remediation works at gully sites. High intensity rainfall events and flooding can damage a site and, at the other extreme, the lack of rainfall( drought) will hamper vegetation growth and, therefore, site recovery.
To assess the impact that rainfall may have had on the remediation of the 24 sites, rainfall data from six nearby Bureau of Meteorology( BOM) gauges was examined. In addition, three of the sites had site specific rainfall data collected by hydrological monitoring stations that CSIRO installed to study the effectiveness of gully remediation on runoff and water quality( Hawdon et al., 2025, p. 13). This data has helped inform this report on rainfall during the monitoring period.
Yearly rainfall totals were around average and there were no regional flood events or droughts that impacted the remediated sites between the time they were remediated( 2019-2021) and 31 December 2024( See Appendix 1. Rainfall data). Total yearly rainfall across all sites during the monitoring years( 2022-2024) was close to the Bureau of Meteorology’ s long-term median. Long term median rainfall for the western BOM rainfall stations( Collinsville Post Office, Gatton Vale and Strathmore) ranges from 626( Gatton Vale) to 706mm annually( Strathmore). During the three years of monitoring all yearly totals from these three gauging stations fell within 573mm( 2024) and 825mm( 2023)- both extremes were recorded at Gatton Vale. Gatton Vale experienced an early start to the 2023 / 24 wet season so
2024 was not particularly dry. Long term median rainfall for the Eastern BOM rainfall stations( Mt Pleasant, Strathbogie and Millaroo) range from 648( Strathbogie) to 736mm( Millaroo). During the three years of monitoring all yearly totals from these three gauging stations are within 703mm and 848mm / year. Yearly rainfall data measured at three gully remediation sites( Mt. Wickham, Glen Bowen and Strathbogie) by CSIRO stations and presented in( Bartley et al., 2025, Pp. 32, 36, 39) reflect the BOM data.( Refer to rainfall graphs in Appendix 1).
However, these average conditions are unlikely to tell the full story. Whilst overall, weather at the sites appears to have been mild and favourable for remediation and revegetation; some sites are likely to have been impacted by short high intensity rainfall events. According to BOM IFD data a 60mm 1.5hr fall at Collinsville is a rare event; it has a 2 per cent AEP( annual exceedance probability; 50yr ARI; ~ 1 in 50yr event). In the absence of rainfall intensity records, the highest daily rainfall totals for the six gauging sites were collated; arbitrarily chosen as daily rainfall over 60mm( see Table 1).
Note that the Collinsville Post Office recorded four of these events between January 2020 and December 2024 while the Mt Pleasant Alert, approximately 33km closer to the coast, recorded nine such events. A similar pattern is evident across the region, with fewer high rainfall events west of the coastal ranges( Collinsville, Strathmore, Gatton Vale) compared to within the coastal ranges( Mt Pleasant, Strathbogie and Millaroo). If some of these daily rainfall totals fell within hours on remediated sites such as during a storm they are likely to cause rilling and scouring, and hinder revegetation progress.
In conclusion, while there were no widespread floods or droughts since initial works were carried out at these 24 sites, evidence suggests that there were high intensity rainfall events that damaged remediated sites, particularly in the initial years after works, 2020 and 2021. Such events are typical for tropical areas and so should be expected and planned for.
NQ DRY TROPICS 5