Hill River EWRs

Due to increasing pressure on ground and surface water resources in the Northern Perth Basin, the then Water and Rivers Commission (now Department of Water; DoW) contracted WRM to determine EWRs for the Hill River near Jurien.

EWRs were scientifically determined using a “holistic” methodology based on the Flow Events Method (FEM). Channel surveys were completed by WRM as well as aquatic fauna surveys to determine the ecological values of the system. The outputs of the field surveys were used to identify the important ecological components to be maintained by the flow regime. These included; channel maintenance, riparian vegetation, aquatic macroinvertebrates, freshwater crayfish, reproductive migration of fish, carbon/energy linkages (upstream-downstream and laterally), and maintenance of water quality. The flow requirements to sustain these ecological values were assessed through the construction of a hydraulic model in HEC-RAS; a one-dimensional, steady-state flow backwater analysis model.

Flow Events Modelling (FEM), using the River Analysis Package (RAP), was then used to estimate the frequency of ecologically significant flow events under the current hydrological regime for the Hill River. WRM reported the flow regimes required to maintain the existing biodiversity and ecological processes, at a low level of risk. WRM also recommended that one of the priorities for management should be to maintain the fresh, permanent pools in the Hill River Springs area, especially in summer, as these pools provide critical refugia for native fish from salinity and seasonal drying that occur further downstream.