Auckland Council catchment planners and stormwater team identified Sunnynook, located within the Wairau Catchment, North Shore Auckland as a significant flooding risk, with a number of residential and commercial properties at risk of inundation, along with SH1. This is due to insufficient detention of stormwater at Sunnynook Park, and significant flooding predicted downstream of this park.
In 2011 AR & Associates Ltd (ARAL) was engaged by Auckland Council’s Stormwater Planning team to undertake an options assessment analysis to address these flooding issues. This primarily involved provision of temporary detention storage within Sunnynook Park for the reduction of peak flows.
After this initial involvement ARAL was further commissioned in 2014 to undertake the preliminary design, which evolved to become a fully integrated project between Auckland Council’s Stormwater and Parks departments. This enabled the initial objective of stormwater management to coincide with sports field improvements within Sunnynook Park and also at Wairau Intermediate School (adjacent to Sunnynook Park). There was also ancillary items to the main works that included additional overland flow path conveyance and landscape improvements.
ARAL has worked closely with the stormwater unit throughout this project, leading the stormwater and civil design aspects, along with various consultation with the multiple affected parties and stakeholders within these major works. ARAL also managed and organised all sub-consultants required for the design works.
The main aspects of design included excavation of approximately 35,000m3 of earth in Sunnynook Park (an existing dry pond) to create more flood storage and optimise the detention function. This will coincide with an upgrade to the field surfaces creating a sand carpet drainage, for better sports facilitation. The cut material from these works will be disposed at Wairau Intermediate School with the objective of levelling the existing fields and improving the playing surface and drainage.
Other works include on site drainage design at Sunnynook Community Centre, which currently experiences localised flooding and drainage issues in winter months. Similarly on Tonkin Drive residential properties are susceptible to overland flows spilling into their land and causing a greater level of flood risk. It is proposed that the overland flow will be conveyed into Sunnynook Park as a safer alternative, through the excavation of a wide swale and concrete path along with the re-profiling occurring on the upper field.
In 2016, ARAL was again commissioned by Auckland Council Stormwater department to conduct the detailed design and construction methodology for Sunnynook Park and associated work elements, to further enhance the design and provide appropriate detail for the project to be ready for construction.
Overall this flood mitigation project will help increase public safety through the Sunnynook Suburb in the Wairau Catchment, where predicted flow velocities and depths in large storms currently considered a risk to people and property.