Management of Sediment in New South Wales, Australia
ABSTRACT The amount of sediment in major New South Wales rivers and reservoirs is relatively low compared to world averages. This is a result of relatively low erosion rates, the sediment coarseness and numerous sediment sinks between the erodingparts of catchments and the rivers and reservoirs. However, in some locations several problems have required attention. These include: sediment blockage of roads and culverts; sedimentation of small reservoirs and recreational lakes; sedimentation on large alluvial fans; river channel damage casued by low sediment supply; and lack of effective government control over soil erosion and sedimentation in the past. Strategies to overcome these problems start with information collection to pinpoint major problems. This enables the preparation of total catchment management plans. These require proper land-use policies, legislation and education of the public for effective implementation.
Denudational history of the south‐central uplands of New South Wales
Summary K‐Ar age determinations on Tertiary basalts provide the basis of a new chronology for part of the south‐central uplands of N.S.W. A master planation surface which truncates a very diverse lithology was formed before Tertiary times, probably during the Triassic. There is evidence neither of the early Tertiary nor mid‐Tertiary planations which figured so prominently in many accounts of the N.S.W. uplands. By the beginning of Miocene times the Lachlan and Wollondilly Rivers had cut to within 80 metres of their present beds. Basalts in headwater valleys show that this part of the Great Divide was well‐established by Eocene times. The sequence of events in this region is strikingly similar to that proposed for the southern part of the Sydney Basin.
Commentary on 'Evolutionary Geomorphology of Australia and Papua-New Guinea'
In his 'Evolutionary Geomorphology of Australia and Papua-New Guinea' Oilier (1979) draws bold, indeed some might say stunning, conclusions. However, the case for several of these conclusions is very weak. For example, the occurrence of Oligocene basalt at 650 m in the Aberfeldy area (Ollier's Figure 9) is obviously far from sufficient evidence to conclude that 'there has been a further uplift of about 6oo m since the Oligocene flow'. The elevation at which extrusion took place simply is not known. The case for the forming of lakes and swamps by back-tilting is no less tenuous. Swamps and lakes not only occur along the eastern continental divide, but are scattered across the width of the eastern highlands, and near Jervis Bay swamps on bedrock slopes occur within 50 m of sea level. Surely, Professor Ollier is not suggesting that anything about the origins of the lakes and swamps can be deduced from what he admits to be the highly biased sampling of Figure io. The most serious flaws in Ollier's account may not be apparent to those unfamiliar with Australian geomorphology. He states, for example, that relict drainage systems on the plateau of Western Australia apparently had their headwaters south of the present coastline and were sundered by the rifting of Australia from Antarctica, but he presents not one jot of supporting evidence. Of the two references cited in that paragraph the first (Ollier, 1977) presents no such evidence, and the second (Van de Graafet al., 1977) presents a conclusion diametrically opposed to Ollier's. Detailed morphological and geological mapping by Van de Graaf and his colleagues showed beyond doubt that the relict drainage systems rose in the centre of the plateau and ran towards the present coastline. Ollier's penchant for ignoring evidence at odds with the speculations of his account is again all too clear in his comments on drainage evolution on the eastern side of the continent. He claims that rivers like the O'Hare and Kangaroo have lost their headwaters and suggests that these headwaters 'have drifted off to the Lord Howe Rise and other continental fragments to the east of the Australian mainland'. Again one looks in vain for the slightest trace of supporting evidence, but has to be content with a fine non sequitur from Griffith Taylor. In fact, the Illawarra scarp which abuts the streams listed by Ollier is not a fault scarp, nor is any feature that could conceivably be such a line of rifting encountered at least until the outer part of the continental shelf (Davies, 1979). Any reduction in the catchments of the quite small plateau streams must have been due to scarp retreat. Indeed, evidence from recent work, not listed by Oilier, indicates that the modern divides are structurally controlled and that divide migration has been minimal (Young, 1977; 1978-I draw attention to the contents of this work, not to its authorship). The resume of climatic change during Tertiary times differs from the conclusions in a recent, detailed review of palynological evidence (Martin, 1978). Oilier states that 'there may