Download Whitepaper - Evaluating the Retrofit Proprietary Treatment Devices.


Long term environmental monitoring and reporting has indicated that water quality in Omaru Creek a small heavily urbanised stream system draining to Tamaki Estuary is impaired. The high level of impervious surface and historic infrastructure development practices in the catchment have led to changes to the natural flow regime and increased pollution from stormwater runoff derived from land uses typically regarded as being high contaminant load generating activities.

Large-scale regeneration that has already begun across the catchment – driven by over 11,000 new homes - offering a once in a lifetime opportunity to deliver substantial stormwater related benefits to the local community.

Those benefits aim to enhance the existing environment, by not only mitigating for the intensification in development but also by addressing the existing stormwater problems. This includes improving water quality by upgrading existing infrastructure and incorporating modern water treatment technology into these existing networks.

The main town centre of Glen Innes has been identified as an area of concern within the catchment. However, available land in the Glen Innes town centre is a significant constraint to infrastructure renewals or retrofitting ‘at source’ or large space-hungry communal water quality improvement options.

‘At source’ retention/detention areas, bioretention devices and in-pipe storage tanks or filtration devices have limited potential within the town centre. Devices that require minimal space requirements including the start of pipe inlet screens and catchpit inserts, in pipe vortex separators or screens and end of pipe trash racks, baskets or netting devices would be more suited.

This paper: 

  • Focuses on the evaluation and assessment of a variety of gross pollutant traps (GPTs) in Glen Innes Town Centre aimed at improving water quality in Omaru Creek by improving the removal of gross pollutants and coarse sediments.
  • Outlines the development of an approach to proactively determine the drainage sub-catchments, to calculate the contaminant loading and their transportation and estimate removal rates of a range of retrofit options to the existing stormwater network informed by literature review.
  • Outlines the development of a methodology to objectively assess and evaluate the suitability of GPTs as retrofit opportunities at a sub-catchment level.
  • Offers (in collaboration with suppliers) a series of different GPTs from two main suppliers based on their relative advantages and disadvantages and treatment performance.
  • Offers a cost-benefit assessment for the selected devices.



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