Authored by Caleb Clarke and Brian Sharman. Prepared for Water NZ 2012 Stormwater Conference.
This paper describes conceptual stream enhancement options considered for Meola Creek as part of the Central Auckland Stormwater Initiative (CASI) in Auckland.
Catchment-wide options included in the CASI options analysis for flood mitigation required either naturalisation, or naturalisation and widening of the main stream. This project considers opportunities to meet the required conveyance objectives, as well as opportunities for naturalisation, daylighting of piped sections, culvert upgrades and improved floodplain storage.
The channel widening concepts explored in this project reveal opportunities to achieve objectives of habitat creation, floodplain engagement, lowered velocities and increased opportunity for amenity and naturalisation. This is achieved by design of wide, shallow, multi-stage channels which slow flows. these show less vulnerability to future changes than pipes or incised channels as they are less sensitive to blockage or extreme events, with a small additional freeboard catering for a greatly increased flow.
Purchase of flood prone and stream side properties would be required to implement such stream widening concepts. However, these could potentially be redeveloped as higher density residential alongside the new stream "green belt" access corridor. Urban design benefits of this redevelopment could include increased amenity, and a more compact urban form.
The wider options assessment of the CASI project is proposing catchment solutions that do not require significant stream widening. However, the naturalisation options will be progressed with consideration of the hydrological regimes required to optimise environmental objectives for the Meola Creek.