A low impact development (LID) is an alternative land development approach for managing storm water, with the aim of reducing the impact of development on water resources. The management practices include infiltrating, evaporating, or harvesting and using storm water on the site where it falls.
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In recent years, research has shown that the individual practice of LID—bioretention, pervious pavements, rain gardens and grassed swales, etc.—are highly effective in managing stormwater runoff, improving water quality, and protecting the environmental and hydrological aspects of developed areas.
LID PRINCIPLES & TECHNOLOGIES
LID uses nature as a model to manage rainfall at the source by implementing a sequence of runoff prevention/mitigation strategies and treatment controls. In brief, there are five principles of LID design:
- Conserving natural areas wherever possible
- Minimising the development impact on hydrology
- Maintaining runoff rate and duration from the site
- Using an array of integrated management practices to reduce and cleanse runoff
- Implementing pollution prevention, proper maintenance and public education programmes
LID technologies include:
- Engineered systems that filter and retain storm water from parking lots and impervious surfaces
- Modifications to infrastructure to decrease the number of impervious surfaces
- Low-tech vegetated areas that filter, direct and retain storm water
- Innovative materials that help disconnect impervious surfaces, made of material such as porous concrete and permeable pavers
- Water collection systems such as subsurface collection facilities, cisterns or rain barrels
EVIDENCE & PROFITABILITY
Researchers from the School of Environment and Energy, Peking University Shenzhen Graduate School investigated the effects of three LID techniques (swales, permeable pavement and green roof) on urban flooding in China, comparing them with the conventional drainage system design. The performance of LID designs was measured under different rainfall characteristics.
The results show that all three LID scenarios were more effective in flood reduction during heavier and shorter storm events, with performances varying according to the location of peak intensity. Swales perform best during a storm event with an early peak, permeable pavements with a middle peak, and green roofs with a late peak.
Anne Guillette, a LEED Accredited Professional, in 2016 Whole Building Design Guide reported that the Somerset community saved US$916,382 from the use of LID. This is one of the oldest communities in the US to implement LID on a large scale (60-acre development) starting in 1995, with 199 homes siting on 10,000 square foot lots. The alternative development pattern that used distributed stormwater management systems yielded six additional lots, which resulted in increased revenues at US$40,000 each.
These additional revenues and overall water management cost savings are more profitable than using conventional stormwater management technique, which directs all storm water to drains to remove it from the site as quickly as possible. With this technique, runoff needs to be managed on the site, so large ponds, or a series of ponds, are required, which will take up a big portion of land.
LID IN SINGAPORE
Post Carbon Institute reported that LID in Singapore contributes 35 per cent of the city’s water supply, with much of it integrated into innovative architecture as well as landscaping for pedestrian or recreational amenities. Two thirds of the city—rooftops, parks, medians, sidewalks, roadways—capture rainwater and convey or pump it via microprocessor-controlled channels or tunnels to 18 reservoirs.
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The design and engineering potential of urban water reclamation through Green infrastructure will not only result in sustainable built environments, but also substantial economic returns, where Singapore can become a global hub of water technologies and innovations.
The Singapore International Water Week 2018 (SIWW) conference attracted more than 24,000 participants from 110 countries and regions, focusing on emerging themes such as smart technology, resource-efficient water treatment and the accelerated commercialisation of innovative water technologies.
It garnered close to S$23 billion in total for the announcements on projects awarded, tenders, investments and MOUs with the attending countries and regions. This was an increase of 37 per cent from the 2014 conference that saw S$14.5 billion in total.
In between these main conferences, there are SIWW Spotlight series—exclusive by-invitation events to continue the dialogue and foster ongoing exchanges on pressing challenges faced by the water sector worldwide. The 2019 delegates include non-domestic water users and their supply chain vendors; key decision makers and R&D leaders.
BARRIERS TO THE IMPLEMENTATION OF LID
Researchers at the Korea Institute of Civil Engineering and Building Technology claim that some barriers for retrofitting the LID practices in urban areas include:
- Difficulty in finding suitable places for LID practices in the existing complex infrastructure
- Lack of design standard practices as most of the research is done in subtropical climate regions, which may not be applicable in Asia
- Lack of knowledge about the LID technology among practitioners and stakeholders; as well as government agencies programmes and initiatives
- Perceived difficulty and high maintenance costs
- Lack of immediate benefits of investing in LID technology
- Lack of technical capabilities and scarce financing
Considering the vulnerability of Asian cities to risks associated with storms and natural disasters, we need to seek solutions to remove these barriers. Flooding and draught not only cause casualties and damage to the environment, but also impact the economy. Urban policies should include more sustainable options and risk mitigations for natural disasters.
Also read: Flooding: Why cities in Southeast Asia need to be more resilient
LID promises sustainable and efficient solutions. Educational workshops could raise the awareness of the importance and benefits of retrofitting LID practices in urban areas. Cooperation and collaboration among engineers—civil, transportation and water engineers, as well as LID professionals—together with public sector’s support and initiatives, are key in carrying out LID practices that will lead to a safe and sustainable future.
Anisa Pinatih – Construction+ Online
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