*4.1. Lined Channel Relocation*

Lined channel relocation has been carried out from as early as the 1800s as a consequence of mining. Early watercourse modification was typically for the consumptive use of water through race construction and sluicing [53]. However, many river channels were also relocated to gain access to alluvial materials underneath the channel, such as alluvial gold deposits. The majority of early river relocation efforts were local, small-scale, and predominantly unrecorded [54]; they were comparable to modern artisanal and small-scale open-cast mining river relocations. Larger river relocation channels were constructed using large timber flumes (Figure 4), whereas smaller river relocations were dug as ditches into the surrounding landscape. Historic river relocation flumes lacked geomorphic characteristics of the natural channel; they were fully artificial and were prone to failure during large floods.

**Figure 4.** River relocation flume (circa 1907–1918) in the Porcupine Mining District, Alaska. (**a**) The flume was 2.4 km long, up to 2.4 m deep, and 7–12 m wide; (**b**) early flumes were prone to failure during floods (Source: Sheldon Museum).

### *4.2. Case Study: Morwell River Relocation, Victoria, AUS*

A particularly challenging type of relocation is where the diverted channel is carried in an elevated flume or channel. A good example of this type of relocation is the Morwell River relocation (MRR) in eastern Victoria, Australia, constructed to access coal reserves at the Yallourn coalmine, Australia's largest open-cut coal mine [55]. The MRR is a 3.5 km channel carried in an elevated embankment that relocated the river through the middle of the open-cut mine pit to connect with the Latrobe River downstream [56] (Figure 5). The embankment was constructed using engineering fill from 13 million cubic meters of overburden that was stripped from the mine itself [56]. The Morwell river has been previously relocated for coal mining at the Hazlewood coal mine, and its present course is the result of multiple relocation attempts.

**Figure 5.** Map of the Morwell River Relocation. The Yallourn coal mine is located to the north of Hazlewood coal mine, where additional river relocation has previously taken place.

The design of the river relocation channel included an artificially meandering channel and a floodplain, with a width that varied between 40 m and 60 m, compared with the 1000 m width of the original natural floodplain [57]. The embankment collapsed during a large flood on 6 June 2012, diverting the Morwell river into the adjacent Yallourn open-cut mine pit (Figure 6). The downstream Latrobe River reversed direction and flowed up the diversion and into the mine pit. The flooding stopped coal production in the state's major coal mine and threatened power supplies. The mine had considerable trouble disposing of the millions of litres of polluted water that entered the mine [58,59]. The flooding reduced production from the state's major coal mine to 25% capacity for 4 weeks [60], and the total cost to repair the MRR was between 109 and 150 million AUD [60,61]. Despite its meandering morphology, the diverted channel developed no natural channel characteristics before its eventual failure.

**Figure 6.** The 2012 Morwell River collapse. Note the meandering relocated channel and associated embankment collapse (Source: Environment Victoria).
