**3. River Relocation Classification**

Relocated channels can either be temporary or permanent [36], with a varying effort to replicate the original river's natural condition. The new channel can be cut across a floodplain, blasted through bedrock, or in some cases, constructed as an embankment. Broadly, relocated river channels can be lined or unlined (Figure 3, Table 1).

**Figure 3.** Classification of river relocation.



Unlined channels use the underlying natural materials to create the new channel (such as relocated channels located within a floodplain or through bedrock). These materials can vary among bedrock, alluvial sediments, or a combination of these materials, occasionally reinforced by hard engineering in places along the channel. Lined channels are constructed using artificial materials, such as timber, synthetic geotextiles, covered pipes (concrete inverted siphons), or hard engineering, such as concrete or rip-rap along the channel. In some cases, a new channel is engineered on an embankment that sits higher than the surrounding landscape (for example, through a mining pit) and can also be accompanied by a series of drop structures to maintain the energy and velocity of the river flow within the relocated channel.

This paper concentrates on the issues surrounding permanent river relocation channels (highlighted in blue in Figure 3), as this type of relocation usually presents the most managemen<sup>t</sup> challenges. Note that artificially cutting off river meanders is a form of relocation, but these short relocations are only considered here where they are cut through bedrock. Note also that the definition of full flow river relocation can be complicated, depending on how much of the flood flows are diverted by the constructed channel. Some just divert up to the bankfull flow and allow the flood flows to continue to pass down the old channel/floodplain section.

We now describe examples of lined, bedrock and alluvial river relocations (with examples of each) from the above classification, and the problems associated with each type. From these examples, and

other sources, we summarise the key managemen<sup>t</sup> challenges associated with these diversion channels. We begin with fully artificial relocated channels (i.e., lined channels) and move to river relocation channels cut in natural rock or sediments.
