The Waiwhetu Stream in Lower Hutt has been subjected to industrial contamination over the last two decades and is prone to flooding during heavy rainfall. Greater Wellington Regional Council has decided to take action to enhance the stream environment and reduce the flooding risk.

Brian Perry Civil was chosen as contractor on the project. The work will involve:

• Excavating approximately 12,000 cu.m of contaminated sediment from the stream bed within working cells formed by sheetpiled coffer dams. 
• Widening and deepening the stream, including erosion protection works. Where neighbouring buildings inhibit widening parallel CFA secant walls will be installed.
• Services into and across the stream will be upgraded through rationalisation, realignment and duplication.
• Ecological enhancements to the area through planting native vegetation, wildlife features and wetlands.

The major challenges to the team on this project are: safely removing about 4,500 truck movements of contaminated sediment and sludge; working around a large number of live services and bridge structures; and working within very strict resource consent conditions.

Work progress in May 2010

1. All contaminated material has been removed from the stream. All coffer dams were removed from the stream, and the stream is now flowing and looking good.
2. Lots of work took place on the CFA secant wall, and it is essentially complete with only 6 out of a total of 235 panels left to go in.
3. Capping and backfilling has progressed following wall installation: 550m of capping beam has been constructed out of a total of 690m. The majority of this length has already been backfilled ready for topsoiling.
4. Ecological enhancements including planting and landscaping are all ready to happen in June over the whole site.
5. At the end of the month constant downpours filled the newly-reconstructed stream to overflowing, but there were no dramas as all our in-stream works were well finished.

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