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Water supply and stormwater management are two significant issues for built environments, especially as our cities grow.

Municipal reticulated water supplies are very costly. As houses grow larger and sections grow relatively smaller, the resulting increase in impervious areas means the volume and speed of stormwater entering streams is increased. More environmentally sensitive and cost-effective options are needed to minimise impacts of this stormwater runoff.

There are many approaches to managing stormwater. These include:

  • Vegetated swales
  • Rain gardens
  • Rain tanks
  • Stormwater retention ponds
  • Permeable pavers
  • Filters
  • Treatment trains
  • Greenroofs
  • Riparian strips

It is also common to have several devices linked in what is called a "treatment train".

Our research also includes assessment of the economics of various stormwater treatment devices.

Catchment management and hydrology

Our approach to urban catchment management considers the interplay of the people that live in a catchment, the environment that is affected by their actions, and the economic impact of management decisions.

The approach is a helpful way of communicating the development process and assessing its positive and negative impacts. We have assisted large-scale developers in achieving more sustainable approaches and directly measuring the success of their good ideas, and have worked with local authorities on long-term visioning.

We are currently developing numerical methods for modelling the potential contribution of alternative stormwater management strategies at the catchment scale to help with stormwater management and better target low-impact design. These will be made publicly available in the near future.

Ponds and detention systems

Constructed stormwater ponds are used in New Zealand to alleviate flooding and reduce the concentration of pollutants in water reaching downstream environments such as estuaries.

Our research has focused on better understanding the physical, chemical, and biological processes that change the hydrochemistry of water in urban stormwater ponds. The results are helping us in better pond planning, positioning and planting to achieve desirable performance. Data are being used for numerical modelling to help predict catchment behaviour.

Bioretention devices

Bioretention devices include raingardens, swales, filter strips and greenroofs; all use plants and substrate to detain and filter stormwater to reduce the impacts on lakes and streams of excessive runoff from roads, roofs and paved surfaces,and provide opportunities for enhancing natural landscape and biodiversity elements in the urban environment.

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Rain tanks

People have relied on rainwater for household, landscape and agricultural water uses for centuries. As communities have become larger and more centralised, community water treatment and distribution systems have gradually replaced the collection of rainwater as our primary water supply. As we have begun to understand the need for sustainable use of water worldwide there has been a renewed interest in collecting rainwater.

Rainwater tanks for both detention and domestic use are being used in several properties in Auckland. At one neighbourhood development potable water supply is via mains connection; however, rainwater is collected (13,500 L tanks) and re-used for toilets, laundry and external uses on 8 of the 13 houses.

Using rainwater:

  • Reduces demand for mains water supply and you save on your water rates
  • Reduces flooding by providing temporary storage for rainwater
  • Reduces wet weather sewage overflows
  • Reduces pollution of our beaches and waterways

Various regulations govern the installation and use of rain tanks and these vary with each local authority. It is advisable to contact your local authority if you are considering installing a rain tank to determine if a building or resource consent is required. Some councils offer incentives or rebates for installation of rain tanks.

Publications

Trowsdale SA, Simcock R 2011. Urban stormwater treatment using bioretention. Journal of hydrology 397(3-4): 167-174.

Voyde E, Fassman E, Simcock R, Wells J 2010. Quantifying evapotranspiration rates for New Zealand green roofs. Journal of hydrologic engineering 15(6): 395-403. ISI:000277743400004.

Voyde E, Fassman E, Simcock R 2010. Fa Hydrology of an extensive living roof under sub-tropical climate conditions in Auckland, New Zealand. Journal of hydrology 394(3-4): 384-395.

Mithraratne N 2010. Rain tanks: are they really green? LG New Zeland local government 46(12): 14-15.

Simcock R 2007. Sprouting greenroofs in New Zealand. New Zealand garden journal 9(2): 17-21.

Ira SJT, Vesely E-T, Krausse M 2007. Life cycle costing of stormwater treatment devices - a unit costing approach for New Zealand. NZWWA journal 152: 44-49.

Mithraratne N, Vale R 2007. Conventional and alternative water supply systems: a life study. International journal of environmental and sustainable development 6(2): 136-146.

Simcock RC, Meurk CD, Smale MC 2005. Maintaining and revegatating roadsides: handbook for road controlling authorities and contractors. Auckland, Landcare Research. 1-80 p.

Zanders J, Taylor M, McLeod M, Simcock R, Robinson B 2003. "Raingardens" for treating urban stormwater. In: Currie LD, Stewart RB, Anderson CWN ed. Environmental management using soil-plant systems : proceedings of the 16th annual workshop held by the Fertilizer and Lime Research Centre, Massey University at Massey University, Palmerston North, New Zealand, 12-13 February, 2002. 16 ed. Occasional report. Palmerston North, Fertilizer and Lime Research Centre, Massey University. Pp. 127-136.

Eason CT, Dixon J, Feeney C, van Roon M, Keenan B, Craig J 2003. Designing out stormwater impacts : can we make low-impact development mainstream? (based on a paper for the Stormwater Conference 2003). Water and wastes in NZ: 48-50.

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