Coolibah (Eucalyptus coolabah) is an iconic Australian tree species and the dominant riparian species in many arid zone river systems, such as in the Lake Eyre Basin. The successful germination and growth (i.e. recruitment) of these trees, which occurs in response to floods, is critical to the ecology of dryland rivers, such as the Diamantina River. Data on the position, elevation, size and reproductive state of coolibahs were collected from field transects in 2014 and 2015 and related to soil data and the Geoscience Australia satellite mapping of inundation frequencies. Multivariate analysis showed that mature trees were most highly correlated with frequently inundated (i.e. near bank) positions and younger trees with less frequently inundated (i.e. distal) positions.  Field observations showed that this relationship was complicated by small-scale topographical features that were favoured sites for recruitment, such as edges of ‘flood runners’ (i.e. shallow floodplain channels that connected with the primary channels) and sand dune – floodplain boundaries. Coolibahs could grow in a wide range of soil types but favoured silt-sand soil types and rarely grew in floodplains dominated by cracking clays with well-developed gilgai structures. Relatively few recruits were identified from the sequence of large flood years in 2009-2011. There was evidence of considerable grazing pressure on the younger coolibahs and also plant moisture stress from the subsequent dry years of 2013-2015. The subdued recruitment response to the 2009-2011 flood sequence highlights the vulnerability of dryland riparian vegetation to grazing and climate change effects.