Report 10 - Executive Summary

Demonstration Projects

Eight stormwater demonstration projects within Waitakere City are described in this report. The demonstration projects represent best practice management solutions for a range of stormwater issues, which range from treating polluted road runoff prior to discharge to streams, to helping prevent flooding in the urban environment.

For many years the management of water quality has been centred on controlling industrial discharges, with inadequate consideration of smaller diffuse sources of pollution from roadways, homes and agriculture, or the importance of good urban design. The focus on reducing flooding and instability has led to stormwater works aimed at efficiently removing stormwater into a reticulation system, mainly consisting of investment in kerbs, channels and piped infrastructure. This has often meant that the adverse environmental impacts upon the receiving waters and aquatic ecosystems have been overlooked.

More recent realisation is that stormwater management also needs to address the impacts of flow volumes, pollution and works on the City's streams, beaches and harbours and their native wildlife. Because Waitakere is a rapidly growing city, a major focus has been on preventing future problems through careful design of new development and its stormwater management systems. An additional challenge within the limited resources available is remedying problems arising from past solutions that have proved inadequate.

The demonstration projects described in this report, offer various soft engineering options for overcoming the stormwater issues using a range of innovative products, methodologies and approaches. The eight projects are briefly outlined below:

1. Formpave Stormwater Source Control - Parrs Park Reserve Parking
   This car-parking project, situated in Glen Eden, heralded the first use of Formpave porous pavers, in New Zealand. Runoff directed via swales to the porous paved area, is filtered through pavers and a layer of gravel beneath, which act to slow stormwater runoff and remove pollutants.
   
    
2. Grasspave Environmental Solution - Massey Community Centre Carpark
   Best management practice was used in the design of a parking area stormwater drainage system, which features a filtration and detention system, based on a series of interlocking recycled plastic grids, filled with sand and grassed.
   
    
3. Manawa Wetland Reserve - Wetland Development in New Lynn
   The objective of this project was to create a natural reserve area, which not only deals with water management, but also provides an interesting and attractive reserve for local residents, whilst retaining and enhancing natural habitat values.
   
    
4. Moselle Avenue Catchment Stormwater Treatment Project - A Technical Brief
   This project demonstrates the viability of retro-fitting an existing stormwater catchment, which includes runoff from the Council's Vehicle Testing, to manage stormwater flows and improve water quality. A sand infiltration basin, bio-swales and bio-detention zone were designed specifically for the site.
   
    
5. On-site Stormwater Management - A Domestic Rainwater Tank
   This project was undertaken to provide a solution to on-site stormwater management when a property was subdivided, and a second dwelling increased the site's impervious areas. The solution was to bury one large tank, to collect and utilise the roof runoff from both the old and new dwellings, mitigating site discharges and providing domestic rainwater use.
   
    
6. Paremuka Detention Ponds - Wetland Pond System
   A system of four ponds was designed to collect stormwater runoff and address stormwater quality from the upper Paremuka Stream catchment, which covers an area of 412 hectares, in Ranui. A large intake structure was constructed to limit the release of water downstream during storms. Integrated landscape planning was a fundamental feature of the project.
   
    
7. Stormwater Quality Pond - Kashmir Road Catchment, Glen Eden
   An on-line pond was constructed in an area, which previously had an open water course and insufficient space to construct an off-line pond. The solution included a deeper channel to aid fish passage and a densely planted wetland to maximise overall efficiency levels and compensate for a greatly reduced pond volume.
   
    
8. Waipareira Stream - Wetland Protection Works
   This stream drains the West Harbour catchment, discharging into the Waipareira Bay in the Upper Waitemata Harbour. On going erosion of a localised rare wetland was occurring as a result of increased urbanisation. The solution involved a carefully balanced placing of a rock weir and partial infilling of the affected streambed to reinstate the wetland and stream environments.

Report 10 - Full Version

Demonstration Projects
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