Effects of water-level changes induced by weirs on the distribution of littoral plants along the River Murray, South Australia

Abstract

In 1988 a survey was made of the River Murray between Locks 2 and 4 (153 river-km) to determine whether the distributions and relative abundances of littoral plants are influenced by water-level variations associated with weir operations. Of 20 recorded plant species, some, including Cyperus sp, and Myriophyllum verrucosue, occurred in regions downstream of each weir and hence were exposed to maximal variation in river levels. Others, notably Typha spp., favoured the regions above each weir, where levels are comparatively stable. The influences of physical channel characteristics such as bank slope, bank erosion and sediment composition and of other environmental factors were not clear. These effects may have been obscured by differences in the natures of the two pools and by a tendency for factors correlated with the water-level gradients to be 'reset' at each weir. Changes in the flow behaviour of the river since 1990 suggest that these survey data may later prove useful in evaluating the effects of high turbidities associated with regulated flows from the Darling River.