Stormwater Infrastructure Upgrade for Carlton Crescent Flood Mitigation

Background Carlton Crescent is located in the beachside settlement of Maraetai in the Franklin Ward. The residential subdivisions were done many years ago with limited stormwater infrastructure being constructed. Stormwater runoff from the properties discharges onto the ground and flows along natural contours of the land.

The roads servicing the residential properties were originally constructed with open surface water drains on either side of the road to collect the surface water from the road and the adjacent properties. These drains in turn discharged into natural overland flowpaths following the natural contour of the land.

Over time these open drains have been removed and kerb and channel and limited stormwater infrastructure was progressively installed by the legacy Manukau City Council. Current Issue To Be Addresed A development recently approved by the Auckland Council at No 60 Carlton Crescent has resulted in 10 new residential lots being created on the land parcel, within an overland flow path.

As a result, some of the new houses constructed on the subdivision are being subjected to surface water flooding. Description of Works To alleviate the problem, it is proposed to new construct kerb and channel along the east side of the Carlton Crescent to direct surface water away from these properties.

Other associated works include stormwater manholes, stormwater pipes, catchpits and catchpit leads, plus a small amount of road widening that requires a granular pavement and surfacing, and associated signs and roadmarking.

The berm behind the new kerb and channel will also be shaped with a mound immediately behind the kerbline to prevent water flowing on the the adjacent properties, should the road water flow over the top of the kerbline. The berm will also be topsoiled and grassed.

Interim Works An earth mound was installed prior to this contract being developed as a temporary measure to prevent flooding of the adjacent properties in the short term. This mound is not to be removed, but it may need to be moved back in places from the edge of the road to allow the new kerb and channel to be installed. Covid-19 Pandemic Additional clauses covering the Covid-19 pandemic are attached to this RFT.

At this point, it should be assumed that the work included in this contract will be carried out under the Government Alert Level 1.