Inter-Basin-Water Transfers significantly reduce flow and sediment regimes to the downstream ecosystem effecting differential channel adjustment at various locations. It is not known how macroinvertebrates adjust to flow regulation, either spatially or temporally, because research is lacking into how morphological adjustment affects benthic habitat. Feedback mechanisms that initiate the adjustment process must first be identified, then the effect on benthic habitat becomes apparent, thus, providing a link to macroinvertebrate response. Since regulation there has been a 95% reduction in flow volume, a complete downward shift in both the flow duration and flood frequency curves and a 194% increase in flow constancy compared to the pre- dam period. Furthermore, Jindabyne Dam traps 99.9% of the total incoming sediment load. Upstream of the tributary the dominant river response was accommodation adjustment with subsequent contraction of the river channel. Associated feedback mechanisms were 'armouring' and vegetation encroachment. Downstream of the tributary response was more complex, with channel contraction through aggradation and specifically the formation of a tributary mouth bar and fan, mid channel lobate bar, transverse bar and in-channel bench. Associated feedback mechanisms were interactions between vegetation and sediment; channel morphology, flow and sediment distribution; and sediment distribution, flow and channel morphology. These processes have had site specific and reach scale impacts on benthic habitat. Macroinvertebrate response to flow regulation was habitat specific (riffle or edge) and seemed to correspond to either site, or reach scale morphological adjustment, whereas, flow constancy seemed to affect edge macroinvertebrates throughout both reaches. Spatially, macroinvertebrates have not adjusted to the post- dam flow regime and temporally, macroinvertebrates have not recovered 30 years after the closure of Jindabyne Dam. How physical processes change habitats and how these impact on a river's ecology and at what scale, are important considerations in river management.
|Date of Award
|Martin THOMS (Supervisor) & Richard Norris (Supervisor)