Statistical description of wetland hydrological connectivity to the River Murray in South Australia under both natural and regulated conditions

Abstract

Summary The effect of river regulation on the connectivity of the South Australian River Murray to its floodplain wetlands was examined using unregulated ‘natural’ and ‘regulated’ river flow data simulated between the years 1895 to 2009. A sample of 185 wetlands was used to calculate a range of connectivity statistics under both simulation scenarios. These statistics summarised the timing and duration of both connection and disconnection, as well as inundated area. Wetlands ranged from being permanently inundated, connected multiple times per year due to both small fluctuations in river level and the annual flood pulse, to flooded with diminishing frequency depending on the size of the annual flood pulse and their position on the floodplain. Under the natural scenario a wide range of wetland connectivity profiles were recorded whereas under the regulated scenario wetlands tended to be either permanently inundated or infrequently flooded. Under natural conditions wetlands that required higher flow before connecting were less frequently connected and for shorter periods. Under regulated conditions a larger proportion of wetland area was permanently connected than under natural conditions, however the annual flood pulse connected a larger area of wetlands under natural conditions. The information derived from this analysis can be used to design wetland management plans for individual wetlands within a river-wide management regime restoring lost hydrological variability.