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inundation frequency estimates due to image availability, 250 m pixel size and mixed spectral
signals, masking by dense riparian vegetation cover > 30%, and other issues detecting
episodic shallow inundation from local rainfall or floods. However, they do provide a first
order minimum look at landscape flooding patterns (Figure 57).
The mapped flood inundation for lower valleys of Crosbie and Eight Mile Creeks and the
Alice River on Oriners Station clearly show that these floodplain valleys are regularly
inundated, on average every two years (Figure 57). This matches local observations of flood
frequency (Section 2.1.2 and 2.2.2). The period of measurement (2003- 2009) had average
rainfall conditions for the period of record (Figure 46), and thus is likely typical. However,
wetter or dryer cycles at the decadal scale could increase or decrease the frequency of
flooding.
Figure 57. Minimum flood inundation frequency data for Oriners and Sefton Stations and part
of the Mitchell fluvial megafan (MODIS satellite imagery, number of times inundated between
2003 and 2009; Ward et al. 2012). Major permanent water body locations and typical dry-season
water clarity estimates from Landsat satellite data (1986 and 2005) are also shown (Lymburner
and Burrows 2008), as are the locations of smaller intermittent palustrine wetlands are also
shown in black (Queensland Department of Natural Resources (QDERM) 2010).
Once floodwaters rise above the banks of anabranch channels along these low-gradient
floodplain valleys (Quaternary alluvium, Figure 48; Cumbulla land system, Figure 50, Figure
55), water easily spreads across the entire valley floor and can reach the edges of adjacent
shallow hillslopes. Flood water at Oriners Station on Eight Mile Creek can reach 2 km across,
since the creek is still partially confined there. Further downstream near the Crosbie/Eight
Mile confluence, floodwater can extent over 7 km across the wider valley (Figure 57). Near
the unconfined floodplains of the Crosbie/Alice confluence, flood water can reach tens of kms
in either direction during floods.
In contrast, runoff and flood water on Sefton Station and the Balurga land system (Figure 50;
Figure 51; Figure 52) are typically confined to the dendritic drainage depressions (dambos)
and valleys (generally < 0.5 km wide), which are carved into the Holroyd Plain. However, the
Working Knowledge at Oriners Station, Cape York
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