Jim Summers

Under the Building (Dam Safety) Regulations 2022, all Classifiable Dams were required to be identified and assigned a Potential Impact Classification (PIC) by 13 August 2024. To achieve compliance, Tauranga City Council (TCC) engaged Tonkin + Taylor in November 2023 to undertake a district-wide dam identification study, complete PIC assessments, and prepare Dam Safety Assurance Programmes (DSAPs) for Medium and High PIC dams.

Using LiDAR and asset database reviews, 156 depressions with storage volumes exceeding 20,000 m³ were identified for further assessment. Under the original size criteria (≥1 m height and ≥40,000 m³, or ≥4 m height and ≥20,000 m³), 90 structures met the definition of a Classifiable Dam. Of these, 59 were owned by TCC, comprising 14 purpose-built water-retaining dams and 45 inadvertent dams such as roadway embankments and sports field bunds.

Following a regulatory amendment on 28 March 2024, which revised the Classifiable Dam threshold to ≥4 m in height and ≥20,000 m³ storage, the number of TCC-owned Classifiable structures reduced to 23. This included 9 Classifiable Dams and 14 Inadvertent Dams. A further 11 structures, although below the revised threshold, were identified as posing potential life safety risks and were assessed accordingly.

The study highlighted the prevalence of inadvertent dams within urban environments and the potential risks posed by smaller structures outside the regulatory definition. TCC is now considering how best to manage these assets within its Dam Safety Management System, balancing statutory compliance with broader public safety responsibilities. Consideration is also being given to the potential implications of including dam break flood information on Land Information Memorandums and the associated effects on property transactions and community expectations.