The property at 1 Sherwin Street, Tauranga, was identified by Tauranga City Council (TCC) as a Depth X Velocity risk property due to the proximity of a 100yr ARI overland flow exceeding the acceptable limit for residential areas (0.4m2/s) and depths in excess of floor levels.

The local layout historically caused the overland flow to concentrate in front of the property in the Sherwin Street sag point before spilling over the berm into the section.

ARAL was engaged by TCC to carry out catchment and peak flow modelling in accordance with TCC’s Infrastructure Development Code, and to develop a range of design solutions to address the 100-year ARI DxV risk in addition to improving the existing stormwater infrastructure in the area.

The final solution involved a grated channel for the safe and effective conveyance of overland flow paths, and the upgrade of an existing 300mm piped outlet using CIPP means. This included the following works:

• Cured In Place Pipe (CIPP) relining works
• Replacement of existing retaining walls that run either side of the stormwater easement
• Installation of a new concrete channel with grated cover and new drop manhole to outfall onto a rip-rap apron;
• Reshaping of footpath, vehicle access and berm;
• Construction of wall fronting 1 Sherwin Street

The project was successfully completed to the required timeframes and approved budgets for TCC.