there were circumstances where there were releases of sediment into the channel, some of which may have been deliberate and others accidental. Any sludge that was released entered into a channel already modified by previous mining, exacerbating the issues of overbank deposition and reducing water quality. Dredging activities also included the straightening of river channels, or when the channel itself needed to be mined, the relocation and replacement of a channel – in the same position with the original dimensions. This latter practice makes it difficult to identify where dredging had altered the channel, however, sometimes the channel was “rocked” to limit channel migration into the subsequent mining pond. Increased numbers of reservoirs for water supply and flood mitigation had been constructed by the time dredging commenced. This suggests that any offsite impacts from sediment mobilisation might be mitigated by storages north of the divide in the west of Victoria, but this was not the case in the rest of the state. In particular in the Ovens River, where the majority of dredges operated, no dams and weirs have been constructed. Thus, any disturbed sediment could have been transported throughout the Ovens River. The Bendigo Advertiser (1906, 2) suggests that Laanecoorie weir was considerably built up with sludge, with about 18 inches (0.45 m) of silt on the bed, and 10 inches (0.25 m) on the sides. More sediment was deposited at the head of the reservoir. When the water level dropped a channel 14 ft (4.2 m) wide and about half a mile (800 m) long was cut through the sludge and the resulting sediment was deposited downstream for about ¾ of a mile (1.2 km) on the riverbed. The differential deposition of sediment in the dredged area led to unworkable surfaces for agriculture and, even with surface pre-stripping, the lower soil structure was not favourable to plant growth. Sub-surface groundwater flows removed layers of fines leading to sinkhole development. The current land use patterns in these areas (Figure 17) shows that they are not being used for intensive agriculture, and it is likely they will never fully recover because of the depth of disturbance. Stage 7: Incision and downstream redistribution (non- dredged sites approximately 1890s, dredged sites approximately 1930s – 80s) Evidence The reduction in mining activities, mining sludge legislation and its enforcement, removal of in-stream wood, construction of levee banks, bank stabilisation and continued regulation of river systems led to rapid incision of channels. The reduction of sediment yield combined with the increased catchment runoff after vegetation clearance meant that both natural and artificial channel deepening occurred and this reduced flood risks. The current stream network in Victoria has many examples of incised streams; however, the exact timing of their incision is not well documented. We have used historic photos, reports and newspapers to suggest that much incision may have occurred before dredging started. In some cases where dredging occurred there was further aggradation in the channel followed by incision when it stopped. Most of the evidence appears to suggest that incision in mined streams had occurred by the 1930s, or was underway by that point in time (Figure 18). Channel incision meant that the sludge deposited on the surface was removed and often the erosion continued down into the original pre-sludge floodplain. The riverbanks clearly show a transition between a darker pre-sludge floodplain and a lighter sludge layer. Similar layering results from clearance triggered deposition followed by erosion, but deposition resulting from mining is indicated by finer clast sizes with less evidence of coarse sediment in flood couplets. To verify the source of the sludge sediment on the Loddon River we used an Olympus Delta XRF gun in the field and in the lab. The stratigraphy of the riverbanks was described, and XRF measurements were taken on the riverbank surface providing Figure 17.  Land-use on historically dredged sites identified using aerial imagery from 2010 and current satellite imagery. Figure 18.  A photograph taken of the Loddon River near Guildford in 1946 showing the light-coloured sludge layer on top of an older and darker floodplain surface (source: River Basin Management Society). Feature Mining to mud 54 PREVIEW JUNE 2019