Gracefield flood protection
Value of project: $1.9 million (increased to $2.6 million)
Client Council: Hutt City Council
Main contractor: Construction Contracts Ltd
Timeframe: 2006, 2007, 2008
Diagram of the pump station discharging water from the Gracefield low lying industrial area.
Background:
Gracefield is one of the Wellington region’s major industrial centres, and a significant contributor to the Hutt City economy. This area had suffered from extensive flooding in the year 2004, resulting in lost productivity and damage to property.
During 2007/2008 Capacity Infrastructure Services undertook a flood management project in the area on behalf of Hutt City Council. The project involved the construction of a stormwater pump station to discharge stormwater from the area when the Waiwhetu Stream is in flood. It also involved the construction of a stormwater delivery main to convey stormwater to the new pump station and back flow protection.
The Gracefield project complements additional Waiwhetu Stream flood protection improvements being investigated by Greater Wellington Regional Council. Although the work at Gracefield will provide an immediate reduction in the flood risk it will not be prevent the Waiwhetu Stream overtopping its banks. The full potential of this project will be realised once the Waiwhetu Stream flood protection improvements are completed.
A programme of testing the quality of the stormwater discharged from the Gracefield area is also being carried out. Sources of contamination identified by this testing programme will be investigated so that remedial action can be taken.
The lead consultant for the job was GHD Ltd and the lead contractor, Construction Contracts Ltd.
The project was scheduled to take place in the 2006/2007 financial year with budget allocation of $1.9million, however, during the course of the project this was revisited with the scope of the project broadened to also include:
- installation of backflow preventors to prevent the Waiwhetu Stream flowing back up and out of the stormwater drains
- minor works to address specific localised flooding problems within the Gracefield area
- the development and implementation of a testing and monitoring programme to locate sources of stormwater contamination
- the development and implementation of a stormwater education programme to local businesses.
As a result the project was completed in June 2008 with the educational programme continuing to run and the budget was increased to $2.6 million.
Challenges:
The elaborate network of underground services in the area provided many challenges to the project team not least of which was where to locate the pump station which in turn would impact on the resource consent process. In the end seven locations were investigated before the final site was settled on next to the Intersection at Parkside Road and Hutt Park Road.
In the course of undertaking the work Capacity Infrastructure Services identified that the existing drains in the area were blocked and in poor condition - without addressing this issue the flood minimisation work would be compromised. An approach was made to the Council to undertake additional work clearing the drains. The Council agreed to fund further work in the area in order to improve the condition of the pipes.
Delays were experienced due to the lengthy process of obtaining resource consent and as a result remaining project funds were carried over to the 2007/2008 financial year.
Success:
Although this project went over time and budget it was considered a success by Hutt City Council because it ultimately resulted in the construction of the stormwater pumping station to prevent a stormwater lake forming in the area when the Waiwhetu Stream is in flood, as well as a new stormwater drain to convey stormwater to the pumping station.