dredge pools, and depressions or linear marks that indicated a dredge track (Figure 15). The absence of floodplain features such as palaeo-channels was also evidence that dredging had occurred (Figure 16). The 2010 land use present at the dredge sites was identified using high resolution aerial (0.15 m2 pixels) and satellite imagery, and was manually classified by the vegetation type and the presence of urban features (Figure 17). Bucket dredges were a floating factory up to 167 m in length. They either sat in the channel or had an artificial lake formed on the floodplain to house them. At the front of the dredge was a chain of steel buckets that could be manoeuvred and raised up and down so that the sediment in front of the machine could be excavated (Figure 14). They did not operate well in stiff clays, but were able to excavate coarse sediment up to the size of cobbles. Clean, reliable and plentiful water was essential for dredging operations, firstly to enable the dredge to float, and secondly for the treatment of alluvium. Water from upstream or from bores was used, and settling ponds both settled fine sediment and provided a clean source of water to be re-used. The largest dredges could dig down into fluvial gravels to a depth of 40 m. During the excavation the dredge separated out coarse and fine sediment using a rotating cylindrical screen. The fines were passed over undulating riffles allowing the gold to settle out in the hollows. Mercury was sparingly used to amalgamate the gold, however, the full details of its use are unknown (Davies, Lawrence, and Turnbull 2015). The excavated sediment was deposited out of the back of the dredge, either into the dredge hole or into a settling dam. The result of this was a complete stratigraphic change in the channel margins or the floodplain, often leaving behind layers of fines topped by coarse sediment. Early complaints about the coarse material deposited near the surface led to the use of more advanced redistributors that put fines on the surface. Advance stripping was also undertaken by removing the top layer of soil and storing it nearby. Once the dredging was completed the soil would be replaced over the surface. The stacked sediment, and the dredge pond itself, were exposed to flooding and were a continuing source of sediment. Interpretation Whilst we understand the likely volume of sediment that was excavated on floodplains, we do not yet fully understand the impact of the early in-stream dredging, or how much sediment entered waterways from dredge operations on floodplains. Clearly Figure 15.  A linear dredge track, and an associated channel diversion, shown using aerial photography (left) and LiDAR (right). (source: Department of Environment, Land, Water and Planning). Figure 16.  A dredged floodplain on the Ovens River indicated by the loss of palaeochannels, shown using aerial photography (left) and LiDAR (right). (source: Department of Environment, Land, Water and Planning). Feature Mining to mud 53 PREVIEW JUNE 2019