Variability in sediment delivery and storage along river courses in Bega catchment, NSW, Australia: implications for geomorphic river recovery

In many catchments in southeastern Australia, alluvial stores have been the dominant source of sediments mobilised in the period since European settle ment. In Bega catchment, on the South Coast of New South Wales (NSW), this has been reflected by dramatic changes to river morphology. Extensive volum es of material have been released and efficiently flushed to the lowland pl ain, with a sediment delivery ratio of almost 70%. However, only 16% of the se alluvial sediments have been flushed through to the estuary, as antecede nt controls on Valley width have resulted in the lowland plain acting as a large sediment sink. The changing nature of sediment source, transfer and a ccumulation zones has varied markedly from subcatchment to subcatchment, Th e volume of material supplied to the lowland plain from differing subcatchm ents is not related to subcatchment area. Rather, the pattern of river type s dictates the spatial variability in storage and transfer. Over 67% of sed iment released has been sourced from just 25% of the catchment, from subcat chments characterised by large valley fills (cut and All River Style) that previously stored extensive volumes of material at the base of the escarpme nt. These parts of Bega catchment were especially sensitive to disturbance. Sediment exhaustion from these parts of the catchment, and from river cour ses elsewhere, has major implications for the geomorphic recovery potential of rivers, constraining what can be realistically achieved in terms of riv er rehabilitation. (C) 2001 Elsevier Science B.V. All rights reserved.