Opotiki Sewerage Project

​The sewers under the Opotiki township were first installed in 1956, and most of the pipework is still in service today. We know that the pipe is reaching the end of its useful design life as the system is not working for the town as it should be. Many in town suffer a loss of service, particularly during heavy rain. We experience overflows and wastewater coming from manholes, gully traps, toilets and basins. Of course, there are associated health risks and there are limits on the ability of the system to accommodate future development.

Council aims to provide reliable and safe disposal of wastewater and to support future development within the district. To achieve this, the Long Term Plan proposes that the Opotiki sewerage system be upgraded. The Opotiki Sewer Project carried out a number of investigations to better understand the issues and to help decide the best way to upgrade Opotiki’s sewerage. 

At the March 2017 Council meeting, Council agree to renew the existing sewers. You can read the media release about the decision or read more about the background to the d​ecision in the Council agenda (​see page 178)

History 

The investigation work had several phases. 

  1. Find out more about the network and the main factors influencing the overflows. This work was completed in 2015 and gave a very clear indication that a major contributor to the overflows was direct inflow into the sewer system.
  2. Select a pilot area to ‘find and fix’ some of the defects to see what happens to the overflow problem in that area.
  3. Evaluate the results of the pilot and see whether the improvements justify the costs or whether a different approach needs to be taken
  4. Further investigations in line with results from the pilot study.
  5. Evaluate and make a decision for the whole of the system.

Picture of Council staff and contractors smoke testing pipes

In 2013-2014 Council engineers carried out private sewer lateral investigations. We assessed the condition of private sewer lateral lines in the Opotiki Township and residents may remember CCTV (camera) investigations and sewer smoke tests.

We also been recorded significant data on rain flow events, river levels, groundwater levels, pump stations, low flows and high flows throughout the township.

Taken together, this data indicated that a big part of the problem may be from inflow and infiltration issues. To better pinpoint the extent of the issue and the sort of solutions we might be able to use, we selected a pilot suburb to work through a ‘find and fix’ programme. 

What was the ‘find and fix’ programme?

Since we know that direct inflow (stormwater getting into the sewerage system) is one of the main contributors to the overflow problem, we decided to select a small suburb, fix the ‘easy’ defects to prevent that water entering the sewers and see how well that solved the issues in that suburb.

We chose the area north of Elliot Street for the pilot area. Council engineers visited properties in the pilot area and talked to ​residents about the pipes that lead from their property into the sewer mains. They investigated the pipes on the property to see if there were any quick and easy repair jobs. These included things like replacing broken gully traps, fixing broken pipes where they had been damaged by driveways or tree roots. Council carried these repairs out at their own cost. Larger repairs, such as full pipe replacement, was noted but not carried out at that time.

Generally, the pipes within a property are the responsibility of the property owner. However, we believed that doing these minor repairs would reduce the amount of stormwater that is accidentally getting in to our sewer system and reduce the pressure on the pipes during rain events. The pilot gave us a better understanding of the extent of the improvement we can achieve if these repairs are carried out throughout the township.

Image showing location of sewer guages in Opotiki township

If you would like to know more about the project, issues with inflow and infiltration, the difference between stormwater and wastewater, ideas for dealing with stormwater on your property, or the data collected on groundwater and river levels in the Opotiki township, please check out the details on the FAQs​ page. Feel free to contact us ​with any other questions about the project.​​​​​​​​​​​​​​

Page reviewed: 27 Mar 2017 1:20pm