4.2.7 Design of Channel Realignments

Where channel relocations cannot be avoided, the realigned watercourse reaches will be designed using natural channel design principles, by qualified technical experts (e.g., fluvial geomorphologist with input from hydrologists, fish biologists and landscape architects as appropriate). The design will involve careful consideration of the ability of the realigned stream reaches to properly convey flow and sediment (ensuring stream gradient, flow velocity/discharge are such that natural geomorphic processes will be maintained along the realigned reach). Natural channel design principles include, but are not limited to the following aspects:

• The new channel sections will be designed to re-instate and wherever feasible enhance the habitat features and functions that occur along the existing channel section and their inter-relationships. Features include morphological elements, particularly pool:riffle complexes, substrates, particularly mixed and coarse materials, and instream and overhanging cover.
• The bankfull and low flow channel sections will be designed to match the existing channel sections (assuming similar slope conditions), or otherwise designed to maintain or enhance existing fluvial geomorphic processes that support fish habitat elements.
• Maintenance or enhancement of fish movement under all relevant conditions (e.g., low flow and higher flows) will be integrated in the design and construction of the new channel section and transitions. Avoidance of potential barriers to movement will consider channel slope and velocity and potential for barriers to develop in the future in relation to channel stability (e.g., either too high/potential for degredation or too low/potential for aggredation).
• The details of the channel installation will be done under the direction of a fluvial geomorphologist. ‘Field fitting’ of the detailed installation of the channel sections and specific habitat components is a critical component of their installation, to ensure the stream channel and habitat maintain or enhance existing conditions and transition easily with the up and downstream reaches.