Innovative infrastructure
Water supply and stormwater management are two significant issues for built environments, especially as our cities grow.
Municipal reticulated water supplies are very costly and 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 often increased. More environmentally sensitive and cost-effective options are needed to minimise impacts of this stormwater runoff.
Integrated urban water management – linking the management of urban water supply, stormwater runoff, and wastewater with the management of natural urban waterways and water bodies – embodies the principles of LIUDD.
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.
The central functions of rain tanks are to reduce stormwater flows, thereby protect natural urban waters and/or reducing demand on the reticulated water supply.
The LIUDD programme found that Auckland’s climate can provide enough water to meet needs in commercial and residential buildings.
A commercial building can meet its full needs, if the rainwater tank overflow, combined with uncollected roof water, exceeds the demand from reticulated services.
In a typical Auckland house, which currently needs approximately 240 m3 per year of reticulated water, a rainwater tank can collect 180 m3 per year on average. Simple demand management technologies such as low-flow fixtures, along with accounting for reduced leakage in rainwater tanks (relative to a reticulated system), can make up the difference.
There is also evidence that rainwater tanks provide educational benefits to the community on the availability of water. Residents using rainwater tanks report increased awareness of water consumption, and, if supply is low, can change their behaviour to reduce demand. Besides water quantity, users of rainwater tanks are also concerned with the health impacts of rainwater consumption. While there have been relatively few disease outbreaks linked to contaminated roof rainwater, research found that following best-practice system design and best-practice maintenance schedules will reduce the level of pathogens and other contaminants entering rainwater tanks.
Our research has provided more insights into the life-cycle costing of rain tanks when compared with reticulated supply. A life-cycle costing study that included the benefit of foregone investment in upgrading existing stormwater infrastructure to cope with increased development found that conventional and LIUDD approaches were similar, but found the LIUDD approach also represented an investment in innovation.
A study that looked only at water-supply benefits showed that continued investment in reticulated water supply LIUDD (including an increased level of demand management) can be up to 80% more costly than investment in rain tanks for supply if the ongoing benefits of water savings are included. Not all infrastructural costs are financial. Energy and greenhouse gas emission costs have also been studied using life-cycle analysis.
Over a 100-year period, concrete rainwater tanks consume the least amount of energy, while reticulated supply (with demand management technology) emits the fewest greenhouse gas emissions. This demonstrates the complex trade-offs that must be considered when planning infrastructure, especially as the most expensive, most energy consuming, and highest greenhouse gas emissions were calculated in the hybrid scenario where investment is made in both reticulated supply and rainwater harvesting.
Vegetated swales
Swales – or biofilters – are vegetated areas used in place of kerbs or paved gutters to transport stormwater runoff and which can also temporarily hold small quantities of runoff and allow it to infiltrate into the soil.
Vegetated swales can serve as part of a stormwater drainage system and can replace kerbs, gutters and stormwater systems. Swales are best suited for residential, industrial, and commercial areas with low flow. Swales reduce peak flows, remove pollutants, and promote runoff infiltration, and they tend to have lower capital costs. While swales are generally used for stand-alone stormwater management, they are most effective when used in conjunction with wet ponds, infiltration strips, and wetlands.
Rain gardens
Rain gardens, preferably planted with native plants, are strategically located to collect, infiltrate and filter rain that falls on hard surfaces like roofs, driveways, alleys, or streets to minimise the negative impacts of excessive runoff from these surfaces on lakes and streams.
Rain gardens – also known as a bioretention device – are designed to take the place of a stormwater system and soak up and filter the water that comes off a roof or paved area.
There is no standard size for a rain garden. One formula provides that the bioretention area should be 5% to 7% of the drainage area that the rain garden is intended to accommodate. A rain garden should be placed near impervious surfaces so that rainwater will drain into the dip or depression. Locate the rain garden strategically near to impervious surfaces, such as alleys, sidewalks, driveways, and under downspouts or gutters, to capture the rain as close as possible to the point where it falls.
Green roofs
Green (or living) roofs are increasingly being legislated for and promoted around the world.
They are effectively a thin planted layer on top of a building or house to achieve maximum stormwater and energy benefits while keeping additional structural costs to a minimum.
New Zealand has very few thin green roofs, but local lightweight substrates, suitable plants, and the benefits for stormwater and biodiversity have been quantified as part of the LIUDD programme.
Using roof space for growing plants has the major benefit of not competing with highly valuable ground-space, while adding value to underutilised space that generates most of the stormwater, reflected heat, and ugly views in a city.
Green roofs are very popular in North America, Asia and Europe to enhance city environments and reduce building energy demands.
Green walls
Green walls, vertical gardens and living building facades, whether free-standing or fixed to a wall, reclaim often disregarded and neglected city spaces (walls and fences) with minimal adverse effect on ground-level usable area. They supply large areas of cooling, insulating and filtering surfaces for a negligible building footprint. This technology has rapidly grown over the last five years with the development of cable and modular trellis systems, and lower maintenance.