The FBP is a 87ha rural area located in the east of the Waiuku ICMP catchment, proposed for rezoning for business use under Plan Change 23. The FBP Structure Plan features an integrated open space system that contributes to stormwater management through a network of wetlands, ponds, open waterways and riparian planting; provides for cycleways/walkways; and links and acts as a buffer between different areas.
Hydrologic/hydraulic modelling confirmed that flooding occurs in the west and south-west of the FBP area due to capacity restrictions in stormwater infrastructure, especially culverts under main roads, and/or the inadequacy or absence of suitable overland flowpaths.
A number of upgrade options were modelled for each area, focusing on pipe/culvert upgrades and/or detention wetlands/ponds, with dam removal and stream restoration also being considered for the Golf Course Creek. These options were then compared on a cost-benefit basis.
The preferred option for the Waiuku Stream involves two large treatment/detention wetlands upgradient of a contractor’s depot. The preferred option for the Golf Course Creek involves two off-line treatment/detention wetlands and twin 2x1m box culverts under Collingwood Road, as this is the only option that achieves the desired stormwater management objectives in terms of stormwater quantity and quality control, erosion protection and flooding. Additional small treatment wetlands may need to be provided in other parts of the FBP. These measures can readily be integrated into the proposed “stormwater/recreation reserves” component of the FBP.