**6. Improving River Relocation Designs**

The poor performance of river relocation channels has prompted greater awareness of new channel designs to fulfil both engineering and channel replication requirements. Here, we present examples of recent best managemen<sup>t</sup> practice approaches to relocation design.

### *6.1. Case Study: Sugar Brook Relocation, Manchester Airport, UK*

The Sugar Brook Valley relocation is an example of an alluvial river relocation that considered the geomorphology and characteristics of a natural river. The Sugar Brook relocation is located next to Manchester Airport, UK. The construction of Manchester airport required the relocation of the Bollin River to facilitate the widening of the first runway [93]. The Bollin River relocation was 780 m long and passed underneath a 25 m embankment. The Sugar Brook relocation is one of two smaller rivers that were relocated to construct a second runway at the airport.

The river relocation was designed to ensure that the majority of the channel is open with a comparable gradient to the original watercourse. A consistent and similar channel gradient is favoured to avoid increased erosion and heightened flow rates within the channel. An appropriate gradient is also essential for maintaining sediment continuity within the channel and maintaining the appropriate stream energy.

The original design of the relocated channel was problematic. Initially, the Sugar Brook relocation required a significant excavation depth to construct the required channel bed level with the resulting excavation (Figure 12a) producing a narrow deep canyon. This design was considered to be geomorphically unreliable due to clay soils and likely undercutting of the toe of slopes, which could accelerate the collapse of high banks [28].

(**b**) **Figure 12.** *Cont*.

**Figure 12.** Sugar Brook relocation at Manchester Airport. (**a**) Initial river diversion design; (**b**) newly constructed valley (in September 1999); (**c**) river relocation 2 years after construction (November 2001) [28].

To improve the stability and long-term recovery of the relocated river channel, a new design was used which considered the larger surrounding landscape in which the river is situated. A new river valley and floodplain was sculpted into an acceptable form (Figure 12b), and then a small meandering river channel was constructed within the new valley floor [28]. The Sugar Brook relocation acts as a larger valley-wide river diversion which looked more natural and stable, facilitating overall positive rehabilitation of the channel (Figure 12c).

### *6.2. Improved Design Using Geomorphic Criteria: Example of the Bowen Basin Mining Relocations*

Mining river relocation channels have received increased scrutiny owing to high-profile cases of failure and poor performance. Contemporary mining is now heavily regulated, but despite rigorous engineering practices, the performance of river relocation channels is a concern to mine regulators. In general, there is a risk of failure during mine operations, and secondly there is the long-term stability and subsequent rehabilitation of the river channel to consider. Mining river relocation channels face increasing scrutiny to fulfil long-term environmental objectives. In particular, mining river relocation presents a noteworthy case study, as there is an emerging conflict between establishing natural values within relocated channels, and the functionality or engineering stability of relocation. The risks associated with mining and river relocation have prompted a series of case studies examining the improved design of river relocation channels.
