Aerial photographs taken in 1945Aerial photographs taken in , 1957Aerial photographs taken in ., 1970Aerial photographs taken in , and 1985 were used to examine the invasion of red gum {Eucalyptus camaldulensis Dehn.) into an extensive, natural grassland. This grassland occupied a high flood frequency stte adjacent to the major River Murray, Australia. Photogrammetric techniques were used to provide information on the successive states of 200 m X 200 m grid cells covering the wetland. The information collected was then assembled into a Markov Chain model of change in the wetland. Prior to 1945 the tree-plain boundary appears to have been stable. The model, extrapolated into the future, showed the almost complete extinction of extensive grass plains, although small-scale intimate mixtures of plain and red gum will exist as a stable form. Analysis of hydroperiods suggested that a major factor in this is the increased summertime levels and reduced winter-spring levels of the River Murray as a consequence of the need for downstream transmission of irrigation water. The affected areas tend to lie between the summertime heights of the river in the pre-regulation and post-regulation days. Although there are few water management options for this particular wetland, it is likely that other riverine wetlands have suffered similar changes but could be managed to avoid some of the adverse effects of such changes in hydroperiodicity.

Abstract. The effect on removal of lower, mid, and upper slope vegetation on the diurnal variation in streamflow from a 46-ha catchment was observed. The diurnal variation in streamflow of the small stream was measurable during the late-spring-to-late-autumn period. The amplitude in streamflow variation reached a maximum in early summer and declined during autumn. Observation of diurnal variations during the periods of higher flow in winter and spring showed that they may occur but were masked by much larger variations associated with storm runoff. Simulation of the characteristics of the flow measurement system showed that diurnal variations can only be studied using V-notch weirs and float recorders during periods of low flow. No effect of the clearing of slope vegetation on the phase of the outflow could be found. However, there was evidence of a significant increase in amplitude, probably due to increased groundwater outflow from the slopes. It was concluded that the diurnal variation is due to transpiration by the riparian and near-riparian vegetation only, and that the lower to mid slope vegetation plays little role in this variation. Simulations suggested that increased amplitude is associated with increased flow rates, and that the amplitude is not directly affected by water use of vegetation on the catchment slopes. It was concluded that the amplitude of the variation is insensitive to changes in slope hydrology and cannot be used to provide insight into deep slope processes.

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Forests of river red gum (Eucalyptus carnaldulensis Dehnh.) occur along the River Murray in Australia. These forests are important for biota, recreation, grazing, and wood products. They occur in a sub-humid to semi-arid environment and require flooding for adequate growth and regeneration. The largest continuous area is the Barmah (Victoria) and Millewa (New South Wales) forest near Echuca (Vic.). Information from maps showing the extent of inundation of Barmah Forest for particular floods was related t o flow data upstream of the forest, and maps showing the distribution of vegetation and forest site quality. Vegetation associations were shown to occur in characteristic flood frequency ranges, with red gum being the dominant species on all but the highest and lowest flood frequency sites. In general, higher red gum site quality was associated with higher frequency of flooding. The extent of flooding depended on the magnitude of peak flows in the river. Regulation of the river since the first filling of Hume Dam in 1934 has caused a reduction in the frequency of flows associated with partial flooding and an increase in the occurrence of small summer floods. Areas with a high flood frequency were most affected. It is possible that the forest may change to types associated with reduced duration of inundation in the long-term unless ameliorative action is taken.

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