An ecosystem approach for determining environmental water allocations in Australian dryland river systems: the role of geomorphology

The allocation of water for environmental purposes is a key management issue in many dryland regions. Many different methods have been developed for determining environmental water requirements but these are not directly applicable to dryland rivers because of inherent flow and habitat variability. An ecosystem approach for determining environmental water allocations in dryland regions is presented in this paper. This four-step process involves (1) a hierarchical characterisation of the river system, to assess what mesohabitats are present and where they are located; (2) the determination of flows that would inundate these habitats and perform other key ecological processes; (3) hydrological analyses in which the key hydrological signatures of the river are identified and the impact of water resource development on these is determined; and (4) the derivation of a water management decision tree that enables managers to allocate water to consumptive users during individual flood pulses (events). It is recommended that the flood pulse should be the focus for environmental flow management in dryland regions. If rivers are indeed nested hierarchies, then a change in hydrological behaviour at the scale of a flood pulse will, with time, extend throughout the hydrological hierarchy. Current environmental flow management strategies in dryland river systems are essentially focused at the flow regime and history scale; this is inappropriate given the inherent flow variability of these systems. The ecosystem approach is outlined for the Condamine-Balonne River, a large dryland system in Australia.