Renewals – Spend Some Money On Investigations Or Just Do Like-For-Like Replacement?

The Park Road Rising Main services approximately 17% of Hastings. It has a conglomeration of six different sewer pump stations all competing against one another to discharge into a single DN375 concrete rising main.

This paper outlines how by taking a more holistic approach to renewal projects and time spent in the investigation phase, a more robust multifaceted solution can be found. This has the potential to save the Client thousands of dollars in construction and operation costs, while also addressing growth and minimizing community disruption.

Rather than diving into a capital works intensive solution of replacing like-for-like, which has often been the historical approach, the project team worked with the Council to step back and invest time and money in the investigation stage. By doing this, the team were able to significantly reduce the capital investment required.

Following rising main bursts, pipe samples were taken and we identified that the Park Road rising main had minimal service life remaining and needed replacing. This coupled with desire from the Council’s roading team to carry out a full road reconstruction, meant that there was strong pressure just to get in and replace the rising main.

By undertaking extensive investigations and strategic planning, we developed the master plan. We looked at the impacted and surrounding catchments. We assessed the surrounding catchments because there were interconnections and complications not readily understood without in-depth assessments. By using a combination of GIS, network modelling, real-time flow monitoring and piezometers we discovered that the main servicing problem could be narrowed down to a single catchment. This catchment had a wet weather peaking factor of approximately 15, three times the accepted limit. In addition the pump stations were in an arms race with one another pushing pumps off their curves in wet weather resulting in a poor level of service.

Our master plan has now been refined and is entering the detailed design phase. It sets out the best way to stage the ultimate goals given the budget and time available while still remaining flexible due to the continuing inflow and infiltration investigations.