A classification of floodplains and wetlands of the murray-darling basin based on changes in flows following water resource development

We present a regional classification of 40 floodplains and wetlands of the Murray-Darling Basin, Australia, based on changes in flows since river regulation and water resource development. The classification is based on a similarity percentage analysis of nine metrics relating to frequency, duration and volume of floods, and seasonality of flows. The major changes in flows were a delay in mean Julian day of occurrence of low flow and reduced variation in occurrence, lower frequency of flood events and reduced variation of flood duration. The spatial distribution of floodplain classes highlights the differential effects of river regulation across the Basin, with greatest change in rivers in the southern Basin, particularly the Murray, Murrumbidgee, and Lachlan, and the least change in unregulated or less-regulated rivers, predominantly in the north. There is generally good spatial concordance between distribution of floodplain classes and the Murray-Darling Basin Sustainable Rivers Audit index of riverine ecosystem health, and the distribution of major communities of waterbirds. Our results suggest, when compared with published reports of ecological condition, that very lowgradient, terminal floodplain wetlands characterized by low discharge volume and anastomosing distributary channels may be particularly susceptible to adverse ecological impacts arising from relatively slight alterations to flows.