Understanding and meeting environmental objectives requires knowledge of the amount of water needed to sustain water-dependent ecological communities. To enhance understanding how changes in water availability can affect floodplain vegetation communities, it is necessary to understand the effects of varying water availability on the different life stages. We used a ‘stock-and-flow’ system dynamics tool to develop population models for river red gum (Eucalyptus camaldulensis ) and black box (Eucalyptus largiflorens) communities in the Murray Darling basin, outputting systems response models for normal, and extreme wet and dry conditions. We interviewed experts to gain knowledge of survival and death rates at the different life stages and used these to populate our models. While mature trees were able to withstand extreme conditions for longer periods, saplings and poles were mostly affected by infrequent flooding or limited duration. Densities of the plants were also a factor in the earlier life stages.  Overall the population of river red gum increased more than the black box with the variability in the interflood interval and flood duration affecting survival across the stages. These models help bridge the current knowledge gap on population dynamics of riparian vegetation by offering two population models for estimating water availability requirements across life stages for healthy floodplain vegetation communities.