Amohia Street stormwater catchment upgrade
Stage one of a three-stage upgrade of the Paraparaumu stormwater network begins in January 2023. The upgrade involves installing larger stormwater pipes to reduce flooding within the Amohia and Ruahine Street catchment areas and help prepare to live with more water due to climate change.
Work programme
We’re installing approximately 805 metres of new, larger stormwater pipes in stages as funding allows.
Stage 1: Iver Trask Place to Amohia Street
The new stormwater pipe needs to be laid under the road to avoid other services in the area. The stormwater pipes and access holes will be installed at about 4 metres deep in places. Due to the high water table, we need to remove water from the work trench. This means pumps and generators will be running near work sites most of the time.
We'll have traffic management in place, but the work will cause some disruption to traffic around the work area.
Stage 1a: Outfall of the Wharemauku Stream along Iver Trask Place to Rimu Road – January–April 2023
Our first task is building a new outfall structure in the Wharemauku Stream in Iver Trask Place. We'll then progress in stages along Iver Trask Place towards Rimu Road.
We'll maintain pedestrian access at all times. Traffic flow will be reduced to one lane, and no parking will be available near the work site. We may need to close the road for a few days while a new access hole is installed.
During the April 2023 school holidays, we'll install the new stormwater pipe under the south-east corner of Kāpiti Primary School’s field.
Our contractor will take all practical steps to minimise impacts of this work.
Stage 1b: Rimu Road from Iver Trask Place to Kāpiti Road – April–June 2023
We'll install approximately 160 metres of pipe progressively along Rimu Road towards Kāpiti Road.
Stage 1c: Kāpiti Road to Amohia Street, July–September 2023
During June we'll install the stormwater pipe diagonally across the intersection of Rimu and Kāpiti roads, and then towards Amohia Street.
Stage 1d: Amohia Street to near 65 Amohia St, September–December 2023
Activity to be confirmed.
Background
The Amohia stormwater catchment is part of the wider Wharemauku Stream catchment, which drains from the hills behind Paraparaumu through the Wharemauku Stream to the sea. Our investigations showed three main areas of interest within the catchment:
- Several properties on and around Amohia Street have a history of flooding during heavy rainfall, with numerous properties at risk of habitable floor flooding to a level of more than 820 millimetres during a 100-year Average Recurrence Interval (ARI) storm.
- Ruahine Street floods in heavy rain due to runoff from upstream hill catchments. The volume of rainwater exceeds the capacity of the existing stormwater network. While most of this flooding is shallow overland flow, it does back up to a level of more than 1.3 metres deep behind the train line. The runoff flows overland, generally as shallow sheet flows, before reaching an open drain downstream of Tongariro Street.
- Several properties on Kāpiti Road and near the upstream open drain are at risk of habitable floor flooding during a 100-year ARI storm.
We've been investigating this issue for several years, and considered several options and routes before deciding on this plan to install larger stormwater pipes.