Kaitaia Wastewater Overflow Reduction Study

Client: Far North District Council

The law of diminishing returns found in wastewater overflow reduction investment (example only )

The law of diminishing returns found in wastewater overflow reduction investment (example only )

Morphum Environmental were engaged to provide a review of the overflows experienced in the Kaitaia Wastewater network and to provide a cost-effective implementation plan to achieve a desired containment standard. This review would enable the Far North District Council to confirm a containment standard and to reduce the number of times the network overflowed each year to meet that standard, using an upgrade solution optimised for cost and effectiveness. Morphum Environmental proposed the optimisation and decision-making study be undertaken using data analysis of model outputs and cost estimates and used our Morphum developed wastewater optimisation toolbox for analysis.within excel, and data visualisation using GIS. 

The Kaitaia wastewater network serves the communities of Kaitaia and Awanui by a reticulated network discharging to a treatment plant located approximately two and a half kilometres west of Kaitaia.

A one-year containment standard is proposed in the Far North District Council’s Long-Term Plan. The method applied to this project was to explore how this one-year containment standard could be met for a range of network upgrade options, and then investigate changes in scope on the most promising options to achieve a higher or lower containment standard. In saying that, almost 70 options were tested with over 200 model runs undertaken. A 1-year containment required a 95% reduction in overflows!

An essential step in the option development was working closely with the operational staff and network maintenance contractors to develop, discuss and, at times, exclude options for network upgrades.

It was recommended that a staged network upgrade would enable an immediate and significant reduction in wastewater overflows. The first stage would achieve a 3-month containment standard which would then allow further network gauging and refinement of the second stage upgrade to achieve the desired ultimate overflow frequency.

Key deliverables:
•    Gap analysis of all data
•    Verification of the operational hydraulic model
•    Existing and future (do-nothing) system performance assessment
•    Options assessment
•    Cost benefit analysis (showing diminishing returns)
•    Non-cost criteria assessment
•    Data and results visualisations using GIS


Nicole Gibson

Brand Manager