Stage 3: Gold rushes (1851–1880) Evidence Data on the initial gold rush is limited to anecdotal information in various reports and miners’journals. Regulation of miners’ activities, and the issuing of mining leases, meant that data needed to be collected on the number of miners and the location of their activities. Much of this information was recorded so that it could be reported to the Government. From records of different mining districts, such as appear in the Mineral Statistics of Victoria (MSV) reports, it is possible to reconstruct the number of miners and the mining techniques that they were using for the period 1859–91. Estimates were then made about the volume of sediment that each different enterprise would produce in order to give an overall sediment yield (Figure 6). Records were originally compiled for each of the gold mining districts (Figure 1). In order to fully understand the impact of the mining operations on river systems these data needed to be separated into river catchments. The VICPROD and VICMINE datasets (Department of Primary Industries c.2002) provided a compilation of around 16 000 gold mines across the state with approximate mining dates and locations alongside other attributes such as whether the mine was mining primary or placer deposits (Figure 7). These data are undoubtedly an underestimate of mining activities, and will certainly miss the earlier phase of artisanal mining, however they do act as a guide as to where most of the mining activity occurred. The estimated volumes for each mining district were distributed across the known mines in the region, and this allowed each mine to be allocated a volume of sediment. This has allowed the volume of sediment produced in each river catchment to be estimated and then compared with other data such as the SEDNET yields (Figure 5). The VICPROD dataset also allowed for the relative position of mines in their river catchments to be determined using the BOM Geofabric. Mined sub-catchments had an average size of 73 km2 and were most common on Strahler 2nd order streams. This means that mines were on average 12 km from the headwaters, and 714 km from the river outlet. In most cases they were in confined or partly confined valley settings with a limited area of floodplain on which to deposit sediment. This meant that the sludge deposition was greatest once the river debouched onto a floodplain after valley confinement was reduced. The impacts of increased sediment yield downstream were reported in contemporary newspapers (available on the TROVE archive). The impacts were so great that in 1886 an inquiry was Figure 5.  The ratio of annual sludge volumes to SEDNET natural load estimates from NLWRA (2001). Figure 6.  The volume of alluvium and quartz mine tailings produced by different techniques in each mining district for the period 1859–1891. Feature Mining to mud 47 PREVIEW JUNE 2019