Amohia Street stormwater catchment upgrade
Stage one of a three-stage upgrade of the Paraparaumu stormwater network began in January 2023. The upgrade involves installing almost 900 metres of larger stormwater pipes to reduce flooding within the Amohia and Ruahine Street catchment areas and help prepare our district to live with more water due to climate change.
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This means we should be able to open Rimu Road to limited one-way traffic travelling south from Kāpiti Road and for Iver Trask Place to return to two-way next weekend. This differs to what we have previously publicised, in an aim to lessen the impact on the wider roading network.
We know this work is disruptive and appreciate your patience and cooperation as we undertake this significant stormwater upgrade to reduce flooding to more than 350 properties.
See Stage 1b for more information.
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 manholes 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 was to build a new outfall structure in the Wharemauku Stream in Iver Trask Place. Work then progressed along Iver Trask Place in stages towards Rimu Road.
In April 2023 we began installing the new stormwater pipe under the south-east corner of Kāpiti Primary School’s field.
Stage 1b: Rimu Road from Iver Trask Place to Kāpiti Road – May–August 2023
We're installing approximately 150 metres of new pipe and two manholes along Rimu Road towards Kāpiti Road. Workers are carrying out construction in four stages, and will need to change traffic flows as the work progresses.
The first stage required s full road closure of Rimu Road just north of Iver Trask Place for up to four weeks while our contractors installed a large manhole in a trench five metres wide and six metres deep.
The following three stages will see our contractors installing stormwater pipe along Rimu Road until they reach Kāpiti Road around September 2023. Detours will be in place and traffic flows will change as the work moves along Rimu Road.
Please take extra care in the area. We thank you for your patience and cooperation as we get this important work done.
Rimu Road stage 1 will take up to four weeks: 21 May to 10 June. See larger image[JPG 203 KB].
Detour route while Rimu Road is closed. See larger image[JPG 126 KB].
Rimu Road stage 2 will take approximately four weeks: 10 June to 16 July. See larger image[PNG 137 KB].
Rimu Road stage 3 will take approximately five weeks: 16 July to 20 August. See larger image[JPG 389 KB].
Stage 2 and 3 allow for one-way only traffic flowing north to south for the remainder of the work along Rimu Road. This is different to what we've previously published. We'll continue to work with all directly impacted parties to make sure any accessibility needs and access to service lanes are addressed before we move onto a new stage.
Rimu Road stage 4 will take approximately five weeks: 20 August to 24 September.
Stage 1c: Kāpiti Road to Amohia Street, September–December 2023
During September we'll install the stormwater pipe diagonally across the intersection of Rimu and Kāpiti roads, and then head east along Kāpiti Road towards Amohia Street.
Stage 1d: Amohia Street to near 65 Amohia St, December 2023–March 2024
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.
