What is Green Infrastructure definition?

One of the major challenges for the growing number of mega-cities (>10 million inhabitants, Li et al., 2015) is water, specifically management of urban stormwater (Larson et al., 2016). Managing urban stormwater is a critical topic because global population became majority urban in 2010 according to data from the United Nations and World Bank. In many older cities, existing wastewater infrastructure is surcharged in wet weather, resulting in combined sewer overflows, when untreated sanitary wastewater dominated by stormwater is diverted into nearby waterways.

Climate change and sea-level rise, are likely to overwhelm this traditional approach to stormwater management, so civil engineers and urban designers have been developing a range of techniques for managing stormwater at its source in order to reduce the level of urban runoff entering the sewer system, include techniques such as Low Impact Development (LID) and Best Management Practices (BMPs), in different parts of the world (Fletcher et al., 2014), that generally call them as Green Infrastructure/Low Impact Development (GI/LID).

Green infrastructure definition and projects are being embraced by many U.S. and European cities as a cost-effective way to control urban stormwater (U.S. Environmental Protection Agency, 2010, 2011) among other challenges. The potential impact of green stormwater systems on biodiversity, traffic accidents, and other city attributes is currently unknown, so valuing the effect of these facilities is germane to policy discussions that attempt to link city greening efforts with quantifiable measures that can be incorporated into the decision making process (Nelson et al., 2009).

Green infrastructure leverages ecosystem functions such as soil infiltration and plant evapotranspiration to reduce or slow the stormwater entering the sewer system (Dunn, 2010; DEP, 2010). However, green infrastructure definition in practice has appeared as part of a novel, environmentally sensitive approach to stormwater management that uses small-scale, natural or engineered technologies and strategies to infiltrate and recycle stormwater runoff.

The green infrastructure should operate at all spatial scales from urban centers to the surrounding countryside (URBED, 2004). The green infrastructures including bioretention basins (shallow, vegetated basins that collect and treat runoff through infiltration and evapotranspiration), green roofs (covered by growing media and vegetation, which infiltrate and evapotranspiration stored rainwater), and permeable pavement (pavement with suficient voids to infiltrate and store water).

However, new infrastructure, both gray infrastructure and green infrastructure, comes at a cost of capital, materials, and energy inputs. In other words, they can reduce local flooding, economic loss, and discomfort at flood events with medium or frequent return periods. In addition to controlling stormwater at the source, they provide many other ancillary benefits to the public and the environment by restoring lost vegetation and disrupted hydrology. This helps restore ecosystem structure and revive ecosystem functions, which may generate a flow of goods and services valuable to humans (Ruhl, Kraft, and Lant 2007).

Some types of green infrastructure have been widely studied and empirically tested. For example, Berardi et al. (2014) assess more than 100 papers published over the last decade about technical, social and environmental aspects of green roofs. Their review suggest that water management is one of the most important impacts of green roofs, particularly in their capacity to reduce stormwater runoff. They explore a wide range of runoff mitigation capacity between 25 and 100 percent.

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Related post: EPA Green Infrastructure