Predicting the outcomes of hydrological change in aquatic habitats of northern Australia
The Challenge
River flows are important for driving the condition and persistence of biota, to support habitats, and to facilitate ecosystem function. In the tropics of northern Australia, flow regimes are highly dynamic with strong seasonal trends. Amongst the high variability of the natural flow regime, flow regime change associated with water resource development and climate change threaten to modify the flow of these natural systems.
Despite the known ecological importance of flow, quantifying the relationships between hydrological change and ecological outcomes remains a challenge. Biota interact with their physical environment differently and have different requirements including inundation, depth, velocity and connectivity which vary across the landscape. Complex landscapes and highly variable flow regimes mean that interactions between flow and geomorphology result in different hydrological and hydraulic characteristics across different settings. This often makes discharge alone a poor proxy for understanding the ecological outcomes of flows in many novel settings and complicates our ability to predict outcomes of change in flow regimes.
This work incorporates both the mechanistic understanding of biotic habitat preferences with correlations of their distributions within the landscape to model outcomes to species flow habitat suitability and other ecological functions in northern Australia.
Our response
Improvement in our conceptual understanding of ecological flow needs is increasingly indicating that ecological flow requirements have a complex relationship with geomorphology and flow dynamics through the landscape, with responses often being non-linear in relation to discharge. To address this, as part of our water resource assessments in northern Australia, CSIRO Land and Water is developing hydrodynamic models that can be used to assess ecologically relevant changes in hydrology and hydraulics, inundation extent and duration, and connectivity along the river and across the floodplain. Linking new ecological models to these large-scale hydrodynamic models provides us with a mechanism to which to explore ecological relationships through space and time, and to enable analysis to compare differences between scenarios in complex geomorphological settings.
Results
This project improves our ability to predict how changes in flow regimes impact water dependent biota and is of critical importance for the assessment of water resource developments, valuing the benefit of environmental water and setting extraction limits for sustainable water use.
This project delivers modelling capability to predict spatio-temporal habitat suitability for a range of water dependent biota, including fish and waterbirds, and a method to quantify river system productivity. While ecological models for assessing the likely outcomes of changes in flow occur for a range of biota in northern Australia, most of these link responses in habitat and/or condition to hydrographs, such as those generated by river system models. These models may make poor representations of space, and can provide a simplistic view of flow habitat conditions within the river channel and out onto the floodplain. Hydrodynamic modelling provides the ability to improve the spatial and temporal inputs to ecological modelling, and improve our understanding, prediction, and representation of ecohydrological change.
The ability to link habitat suitability models to the outputs of hydrodynamic models will support governments, industry, and communities in seeking improved management of water resources in northern Australia. It will improve the capacity to deliver innovation to the work of CSIRO and Land & Water and leverage from existing investments in developing hydrological methods, including hydrodynamic models. Outputs of this work will support future investments in ecohydrology by developing a new approach to be used to assess the outcome of changes in flows.