Water Management Projects
Blue-green infrastructure using “biofiltration” is increasingly used to design stormwater management and manage natural waterways to lessen flood risk, and improve water quality, in the form of swales, overland flow and retention ponds/rain gardens.
There is an associated use of landscaping to enhance biodiversity, create eco-corridors and improve amenity. Wetlands could include the old wetlands in Mangawhai Community Park and the Mangawhai Golf Course.
The preferred option for water supply is to continue to rely on water harvesting for household use with no extension of the public supply. This will require new houses to be capable of collecting rainwater in sufficient quantities. Communal water storage for firefighting is supported. This water could also be sourced from MCWWS for emergencies, via connection to the Fire Station to be sited on Mangawhai Community Park.
The intent is that no untreated stormwater flows directly into the harbour or sea. This is a Council activity that has seen the least investment in Mangawhai over time, with plentiful remedial work required.
While more knowledge is needed to determine the best response, the preferred approach is, where practical, low impact bio-mechanisms (biofiltration) to manage stormwater. This is not always possible because of differing ground conditions. Where there is insufficient soakage, or workable overland flow, piped network may be necessary.
Where possible, drains/overland flow paths will be naturalised into streams with biodiverse riparian planting. Roads will be the first choice for overland flow in storm events. Retention ponding/swales will be used to treat stormwater before it soaks into groundwater or flows into the harbour where this will work. Otherwise a mechanical treatment device may be necessary.
The Stage One projects for the Water Management work stream have been scoped and identified to be the installation of 100-year design storm water pipelines that will mitigate current issues with storm water and sewage discharge in Eveline Street and Quail Way.
Eveline Street
This Stage One project for the Water Management work stream has been scoped and identified to be the installation of 100-year design stormwater control that will mitigate current issues with storm water and sewage discharge in Eveline Street.
The start date is still to be confirmed, due to private works taking place nearby and the need to allow any overlapping projects to be completed before proceeding. Road work may temporarily block access to properties. Track and discharge work will temporally close the track to the beach and may block access to some of the beach area. More information will be available when the start dates are known.
**Detailed images in fact sheet below
Quail Way
The first Stage One project of the Mangawhai Community Plan for Water Management, was completed in conjunction with Abergeldie Harker Limited. 1200mm and 900mm stormwater pipelines have been installed on Quail Way, along with swales and energy dissipaters at the outfall on Breve Street; these are positioned to alleviate the flooding issues that were prevalent on the site.
The area had been flooding with regular occurrence towards the end of March 2017 due to the ground water table being inundated, and its inability to drain away under the frequency of rain storms. This new work is part of wider stormwater upgrades across the district.
At the same time, contractors did some base level work to remediate the Breve Street coastal access walkway, this will receive future improvement in stages to come.
Before
Mangawhai Waste Water Treatment
The Mangawhai Community Wastewater Scheme is being managed as business as usual and will be reported on outside of the MCP Project.
Project |
Description |
Priority One 2018 - 2020 |
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Overland flow path/ ponding location and protection |
Develop a stormwater bylaw that allows intervention in areas where legacy issues require resolution. Use easements to protect existing overland flow not effected by development (or re-direct to the road corridor if possible). Formalise and protect overland flow paths within roads and incorporate overland flow function into the road corridor as part of future road upgrading works. |
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Investigate and develop where appropriate wetlands/ponding to collect stormwater in the Mangawhai Heads area that would otherwise go directly into the harbour |
Re-water the original wetlands within Mangawhai Community Park from overland flow paths. Look to create wetlands as public parklands on land around the Mangawhai Golf Course and Mangawhai Community Park Improve outlets and operation of stormwater to Golf Course wetlands. |
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Engineering standards revision |
Revise engineering standards to include: - Testing, design, construction, monitoring and maintenance of soakage systems (biofiltration) - Protection of overland flows from development - Protection of amenity and character. |
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Priority Two 2021 - 2024 |
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Improve knowledge and remodel performance (Catchment management plan) |
Identify more clearly existing overland flow paths. Gather accurate information of current infrastructure and systems. Understand soakage capacity including effects of groundwater levels and soil types. Complete downstream assessments. Gather and log as-built information in GIS. Identify new or improvements to stormwater system and implement them |