SEEING THE UNSEEN – OPPORTUNITIES FROM A HOLISTIC NATIONAL VIEW OF STORMWATER ASSETS AND FUNCTIONS

A. Allan (WSP), P. Christensen (Storm Environmental), P. Eyles (DIA), K. Hill (Tauranga City Council), T. McCartney (Pracxus), H. Shaw (Beca)

ABSTRACT

The 2022 Water Services Reform Legislation required Territorial Local Authorities (TLAs) to create allocation schedules. These would enable newly formed Water Entities and TLAs to deliver their legislative responsibilities. To facilitate the holistic management of stormwater, critical information about catchments, including piped networks, natural drainage, conveyance pathways, and water quality treatment, was vital for the Water Entities.

TLAs shared their geospatial stormwater network data with the Department of Internal Affairs. The legislation in place at the time required the identification of stormwater assets and functions that would transfer to new entities (i.e. core urban networks) and those that would remain with TLAs (e.g. transport stormwater assets).

The automated analysis of 3.1 million stormwater assets from 66 TLAs, using a standardised approach, unveiled, for the first time, a comprehensive national overview of New Zealand's stormwater networks. This included 820,000 private stormwater assets, 570,000 transport-related stormwater assets, 63,000 assets in rural areas, 44,000 waterway features, 6,000 dedicated stormwater treatment devices, and 4,000 mixed-use stormwater treatment devices.

The data standardisation and result validation processes revealed large differences in nomenclature and information detail between council datasets.

The initial TLA data upload generally included hard assets, limited to engineered structures and piped networks, and data set gaps relating to ‘soft’ infrastructure and mixed-use assets including watercourses and wetlands that form part of the managed catchments.

There were important information gaps about natural urban watercourses and overland flow paths. Watercourses serve a critical conveyance function within catchments and are part of both water quality and flood management. Watercourses are complex due to uncertain responsibility between TLAs, Regional Authorities and private landowners. Similarly, unformed overland flow paths for stormwater were absent from data sets; information on these exists at differing levels across the country.

Data gaps were made apparent once data was in a visual format. This enabled quick dataset comparison and feedback from council staff was positive regarding the ability to notice gaps and update information. Having standardised data and automated tools to analyse data meant that the updates were fast and efficient.

This paper provides a transformative perspective on national stormwater infrastructure management. The identification, comprehensive analysis, and mapping to a common nomenclature of 3.1 million assets, including private, transport, and rural, offers a groundbreaking national overview. The standardised approach and utilisation of automated assessment tools to identify ownership and maintenance responsibility addresses critical challenges within the industry, tackling discrepancies in nomenclature and information detail. The ability to visualise diverse datasets facilitates the identification and rectification of information gaps, like the large gaps found for ‘soft’ infrastructure, or individual data gaps in hard assets. By benchmarking at a national scale, this work forms a foundation for the establishment of a consistent approach to regulation and efficient management of stormwater through the creation of a common language and assessment approach. If a consistent approach like that outlined in this paper is adopted nationally, this will help to optimise the use of the limited resources available in the New Zealand stormwater industry.