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Impact of Built Environment on Natural Environment

Environmental Engineering is based on the sound principles of multi disciplinary fields including Geology, Hydrology, Biology, Physics, Chemistry, Engineering, Medicine, Management, Economics, Law and Biotechnology etc. It involves water supply, pollution control, waste management, recycling, waste disposal, waste treatment, radiation protection, industrial hygiene, sustainability and public health. In simple terms, it can be defined as-"the application of science and engineering principles to protect and utilize natural resources, control environmental pollution, improve quality of the environment to enable healthy eco-system and comfortable human habitation"

The Ecosphere which we normally refer to is the combination of: Lithosphere, comprising of outer shell of the earth, hydrosphere, comprising water over and under the surface of the earth, Atmosphere, comprising of large amount of gases surrounding the earth and lastly, Biosphere, comprising of all the living organisms on earth. Human beings interact with the environment in many ways impacting and affecting both the environment and human health physically, psychologically, socially and culturally.

In Environmental Engineering, the environment can be classified as - Natural Environment and Built Environment. Natural environment comprises of all living and non-living things naturally existing in a given environment while in a built environment, it refers to human made surroundings that help human survival.

Our built environment and its interactions with the natural environment are complex and have a massive impact on the world around us. Hence sustainability is a complex concept which encompasses not just energy but all the resources needed to support human activity. A large part of building sustainability is concerned with addressing the global warming that is driving climate change; using energy conservation and techniques such as life-cycle assessment to maintain a balance between capital cost and long-term asset value. It is also about enhancing biodiversity, creating spaces that are healthy, economically viable and sensitive to social needs. Rather than constantly battling against the natural environment, we need to start respecting natural systems and learning from ecological processes: creating a better balance between human need and the wider environment.

This article confines itself to some aspects of Built Environment.

Introduction

Built Environment

The built environment is an important factor to study because of its tremendously harmful impact on the natural world. Buildings, which make up a large portion of the built environment, account for nearly forty percent of energy consumption alone in the developed world. Of this, residential buildings are by far the most responsible, accounting for well over half of the consumption. As a result, the average household spends at least $2,000 a year on energy bills over half of which goes to heating and cooling.

In addition, buildings contribute over one third of the developed world's carbon dioxide emissions. Smog may not always be visible, but one cannot escape the discomfort and mugginess of heat. Indeed, thermostats in cities with one million people or more can rise anywhere between one and three degrees Celsius as a result of excessive carbon emissions.

Land use is also an important indicator of the toll that the built environment is taking on the environment. It is a known fact that urbanized land approximately quadrupled in size from 1945 to 2002, increasing at about twice the rate of population growth over this same period. The relative decrease in agricultural land is equally disconcerting. And without locally-sourced agriculture, it becomes difficult to feed ever growing cities.

The Impact

The built environment has direct and indirect effects on the natural environment. Urban form directly affects habitat, ecosystems, endangered species, and water quality through land consumption, habitat fragmentation, and replacement of natural cover with impervious surfaces. Development patterns and practices also indirectly affect environmental quality since urban form influences the travel decisions that people make. Certain patterns of development encourage increased use of motor vehicles, which is associated with growth in emissions of air pollutants and the greenhouse gases that contribute to global climate change. Air pollution and climate change, in turn, can adversely affect water quality and habitat.

Around half of all non-renewable resources mankind consumes are used in construction, making it one of the least sustainable industries in the world. However, mankind has spent the majority of its existence trying to manipulate the natural environment to better suit its needs so today our daily lives are carried out in and on constructions of one sort or another: we live in houses; we travel on roads, work and socialise in buildings of all kinds. Contemporary human civilisation depends on buildings and what they contain for its continued existence, and yet our planet cannot support the current level of resource consumption associated with them. Tables 1 and 2 refer to estimates of resources used in buildings worldwide and global pollution that can be attributed to buildings.

Resource	(%)
Energy	45 - 50
Water	50
Materials for buildings and roads (by bulk)	60
Agricultural land loss to buildings	80
Timber products for construction	60 (90% of hardwoods)
Coral reef destruction	50 (indirect)
Rainforest destruction	25 (indirect)

 

Table 2: Estimate of global pollution that can be attributed to buildings

Pollution	(%)
Air quality (cities)	23
Climate change gases	50
Drinking water pollution	40
Landfill waste	50
Ozone depletion	50

Land Use Impact

Development patterns have changed dramatically over the past century. In the early 1900s, urban areas tended to be compact, with a strong central business district and industrial facilities serving as large employment centers. Communities tended to be walk able and contained a mix of houses and convenience services such as shops. Today's metropolitan areas extend over large areas and employment is frequently widely scattered. People must rely on automobiles for access to jobs and services, as residential and commercial areas are separated, and the pedestrian environment is increasingly inhospitable. In many regions, urbanized areas have expanded dramatically. The reasons for these dramatic changes in urban form are numerous, including income increases, living style preferences, and public policy on transportation investment, housing, and taxes that have facilitated these trends.

Direct environmental impacts of current development patterns include habitat loss and fragmentation, and degradation of water resources and water quality. Building on undeveloped land destroys and fragments habitat and thus displaces or eliminates wildlife communities. The construction of impervious surfaces such as roads and rooftops leads to the degradation of water quality by increasing runoff volume, altering regular stream flow and watershed hydrology, reducing groundwater recharge, and increasing stream sedimentation and water acidity. A 1-acre parking lot produces a runoff volume almost 16 times as large as the runoff volume produced by an undeveloped meadow.

Mobility Impact

Vehicle travel has increased substantially in recent decades. Development patterns have contributed to increased vehicle use. Investment in highway capacity encourages more vehicle travel by temporarily reducing travel time and costs. Low-density development with significant distances between housing, jobs, schools, and shopping make walking, bicycling, or use of transit difficult for most trips. Urban design that emphasizes the automobile, such as large surface parking lots, wide streets, and a lack of sidewalks, make vehicle use more comfortable and safer than walking or bicycling, even for short trips.

The environmental consequences of vehicle travel and dependency include degradation of air quality, greenhouse gas emissions and increased threat of global climate change, and noise. Emissions from vehicle travel pose serious threats to ecological and human health. In 1991, air pollution from highways is estimated to have caused between 20,000 and 46,000 cases of chronic respiratory illness. Atmospheric deposition of vehicle pollutants into bodies of water also adversely affects water quality. The economic costs of air pollution in terms of health impact, crop damage, and building and materials damage are significant.

Transportation is also a significant source of greenhouse gas emissions. The accumulation of greenhouse gases in the atmosphere is widely associated with changes in global climate that could raise sea level and increase the frequency and severity of extreme weather events worldwide. Although motor vehicle emissions of most air pollutants have declined since 1970 due to improved technologies and cleaner fuels, increasing VMT (Vehicle Miles of Travel) growth threatens to reverse this trend. Greenhouse gas emissions from motor vehicles have been increasing rapidly, fueled by increased vehicle travel.

Hydrology Impact

Development in a watershed changes natural drainage patterns. Increases in impervious areas associated with development increase the volume and the rate of surface water runoff. In a study of 40 runoff monitoring sites across the nation, a 1-acre parking lot was found to produce a runoff volume almost 16 times as large as the runoff volume produced by an undeveloped meadow. Peak discharge, velocity, and time of concentration of storm water runoff were also found to be much greater. Furthermore, transportation-related impervious surfaces seem more often to exhibit a greater runoff volume than disconnected rooftop-related imperviousness of the same surface area. Channelization projects, such as concrete retention walls or lining along stream beds, channel realignment, and diversion of streams through culverts, also increase flow velocities.

Increased peak discharges and shorter lag times between storms and the resultant runoff lead to larger and more frequent incidents of local flooding. Because the faster runoff prevents percolation of water that would normally feed regular stream flow, floods are followed by longer periods of below-normal stream levels. Lower flows during periods between storms may affect the aquatic habitat and the ability of a stream to dilute toxic spills. Higher flows often result in stream bank erosion, increased sedimentation in the channel, and decreased stability. Streams may widen to two to four times their predevelopment width if storm water from developed areas is uncontrolled. Research models suggest that a threshold for urban stream stability exists at about 10 percent site imperviousness.

Sediment pollutant loads created by increased erosion can cause a broad range of impacts in receiving waters, including reduced water storage capacity, impaired dissolved oxygen for aquatic organisms, decreased light penetration, increased need for dredging, increased costs for water treatment, accumulation of pollutants, and adverse effects on fish and shellfish. When runoff increases in volume and velocity, soils have less opportunity to absorb storm water. This loss of groundwater recharge can reduce residential and municipal water supplies, decrease base flow into stream channels during dry weather, and threaten the health of local wetlands that rely on groundwater to maintain wet conditions during dry periods of the year.

Water Temperature

High volumes of runoff from hot paved surfaces and rooftops may cause a rapid increase in surface water temperatures. Discharges from storm water management devices, which retain collected runoff in unshaded ponds, also may increase stream temperatures. Increased temperature can harm fish and other aquatic life. Water holds less oxygen as it becomes warmer, which may affect habitat and make the water more susceptible to oxygen-demanding pollutants. Sustained water temperatures in excess of 70°F are considered stressful or lethal to many cold water fish species and stream insects. The availability of food, attendant life cycle chemistry, and water quality changes are all affected by water temperature.

Green House Gas Emissions

Greenhouse gases from human sources threaten to alter Earth's atmosphere, since the planet's ecosystems cannot absorb such elevated levels of these gases. Carbon dioxide (CO₂) is one of the primary greenhouse gases emitted by humans. The accumulation of greenhouse gases in the atmosphere can lead to global climate change (also called "global warming," since one outcome is an increase in the average atmospheric temperature). The results of global climate change are potentially dramatic. Increases in atmospheric and oceanic temperatures might raise sea levels and alter associated weather patterns, which in turn could increase the frequency and severity of extreme weather events worldwide. Such changes might alter current patterns of land use and human activity, as well as ecosystems and natural habitats. Even an increase of a few degrees can lead to dramatic changes in climate.

The total global warming since the peak of the last ice age 18,000 years ago was only about 5°C. In 1990 EPA estimated that a doubling of atmospheric levels of CO₂ would lead to an increase in average temperatures of anywhere from 1.5 to 5.5°C. The Intergovernmental Panel on Climate Change, USA (IPCC) in 1995 predicted an increase of about 2 to 3.5°C between 1990 and 2100. Transportation is a significant source of greenhouse gas emissions.

Global climate change may have severe consequences for ecosystems and economies around the globe. IPCC models predict a rise in sea level over the next 100 years of 20 to 86 centimeters, with the most likely case of a rise of 50 centimeters. EPA predicts a median estimate of 45 centimeters. Such a rise would inundate wetlands and lowlands, accelerate coastal erosion, worsen coastal flooding, threaten coastal structures, raise water tables, and increase salinity of rivers, bays, and aquifers.

Low-lying coastal areas would be the hardest hit, since a small sea level rise could put large areas under water. EPA estimated that a 50-centimeter sea level rise would inundate 5,000 square miles of dry land and 4,000 square miles of wetlands in the United States. Total monetary losses caused by a 1-meter rise are estimated to be between $270 and $475 billion, not including future development. The rises in global average temperature predicted by EPA, the IPCC, and the U.S. Congress Office of Technology Assessment could increase average global precipitation by as much as 7 to percent. Predictions suggest that precipitation would increase at high latitudes and decrease at low to middle latitudes, increasing the potential for more severe and longer-lasting droughts.

Effective Built Environment

Effect of built environment on natural environment can be reduced by adopting proper strategies and can be enumerated under following six heads. Important ones are discussed.

• Compact development
• Reduced impervious surfaces and improved water detention
• Safeguarding of environmentally sensitive areas
• Mixed land uses
• Transit accessibility
• Support for pedestrian and bicycle activity and other micro-scale urban design factors

Compact Development

Compact metropolitan development generally means that the space needs of a population can be satisfied with less land area. Compact development can take various forms. From a regional perspective, metropolitan areas may limit the extent of development so that it does not extend too far into rural areas. New development can be targeted to specific areas, such as re-developable areas within established communities.

There are three techniques namely, Infill development, Brownfields redevelopment and Cluster development.

• Infill Development - Infill development occurs in locations where some development has already taken place and infrastructure is already in place. In urban areas, infill development is typically executed by converting old buildings and facilities into new uses (redevelopment) or by filling undeveloped space within these areas. For example, infill development in an urban area, where parking lots are replaced by buildings, parks, and/or garages.

• Brownfields Redevelopment - Brownfield sites are different from other urban infill sites because of uncertainties about environmental liability and clean-up costs. Site owners, developers, and lenders often avoid investing in brownfields because of fear of contamination and the costs associated with it. Clean-up costs of brownfields vary widely depending on site size, the intensity and type of contamination, and the nature of the remediation required. Rather than developing brownfields, firms and investors instead turn to surrounding areas and undeveloped greenfields or relatively untouched and uncontaminated land.
• As a particular kind of underdeveloped land, brownfields have received significant attention as both a   problem and a potential source of multiple urban benefits. Brownfields are "abandoned, idled, or underused industrial and commercial facilities where expansion or redevelopment is complicated by real or perceived environmental consequences." Brownfields redevelopment has potentially strong repercussions for environmental quality and community life since undeveloped brownfield sites may be a health threat or a discouragement to further investment in established urban areas.
• Cluster development- In newly developed areas, clustering development into concentrated areas can protect natural habitat. Cluster developments are built at gross densities comparable to conventional developments but leave more open space by reducing lot sizes. Square footage of buildings and residential and commercial capacity may remain the same, but compact clusters reduce the dimensions and geometry of individual lots and shorten road lengths, as shown in Figure 4-2. In the large-lot development, private lots take up the entire area of the subdivision, while in the compact development; private lots take up only a portion of the total land area, allowing more than half the land area to remain in its natural state. Clustering has a number of advantages in addition to the environmental benefits discussed below. One of the main advantages of cluster development as a conservation tool is that it does not take development potential away from developers, since it changes the arrangement but not the number of units permitted on a property. It also can reduce costs for developers by requiring fewer miles of roads and, if applicable, water and sewer lines. Furthermore, cluster development does not require large public expenditures to purchase development rights.

Reduced Impervious Surfaces

Impervious surfaces have substantial environmental impacts. Impervious surfaces increase peak discharges, pollutant loads, and volumes and velocity of runoff. In areas with large paved surfaces (such as parking lots), high volumes of storm runoff are carried out through storm drains into watercourses, starting soon after the storm begins and continuing during the duration of heavy rainfall. During periods of heavy rainfall, widespread coverage by impervious surfaces can increase the likelihood of serious flash flooding. Absorbing runoff where it originates helps reduce flooding and maintain the water table, wells, and creeks.

Compact development often minimizes or reduces impervious land area, and devotes less land area to roads and may also devote fewer acres to buildings if residential or commercial space is built up vertically rather than out horizontally. In addition to compact or cluster development, other variations in built environment designs can reduce impervious cover and improve storm water infiltration and detention. Techniques for reducing impervious surfaces and improving water detention include:

• Modification of street standards and parking requirements
• Use of porous surfaces rather than concrete and asphalt
• Use of open and natural drainage systems
• Landscaping that helps retain soil moisture and conserve water usage

Safe Guarding Sensitive Areas

Minimizing environmental impacts not only involves decisions about how much to build, but also where to build. Some locations lessen direct effects on habitat and water resources. Minimizing harmful environmental impacts may mean forestalling development in sensitive natural areas such as streams, wetlands, floodplains, steep slopes, mature forests, swamps, critical habitat areas, and shorelines. Environmentally sensitive areas have benefits beyond scenic value. Riparian buffers along rivers and streams, for example, are often critical habitats. One study indicates that nearly 70 percent of all vertebrate species use riparian areas in some significant way during their life cycles.

Mixed Land Uses

Standard zoning separates uses into distinct zones for residential, commercial, or industrial uses. In contrast, mixed-use development locates land uses with complementary functions close together. Complementary uses may include housing, shopping, offices, restaurants, and movie theaters - any destinations that people travel to on a regular basis.

Techniques for / Types of Mixed Use Development Mixed use development can occur on a number of levels: site-specific, neighborhood, or sub-regional. On a site-specific basis, individual buildings or complexes can be designed to incorporate a variety of uses. For example, a single building might include apartments, offices, and retail. At the neighborhood level, mixed-use development refers to the arrangement of different uses across several blocks or acres of land so that they are not physically isolated from one another. Finally, at the

Sub-regional level, mixed-use often aims to balance jobs and housing so that people have the opportunity to live closer to their places of employment.

Transit Access

Transit systems that are well designed and operated can reduce vehicle travel, resulting in reduced criteria pollutant and greenhouse gas emissions. A transit bus carrying 40 passengers requires only about one-sixth the energy consumption it takes to transport each person in a private vehicle. Transit also helps to reduce traffic congestion. One full 40-foot bus is equivalent to a line of moving automobiles stretching six city blocks, and one full six-car heavy rail train is equivalent to a line of moving automobiles stretching 95 city blocks (assuming traffic operates at 25 mph). Transit provides mobility to individuals of all ages, income levels, and abilities. With an aging population and increased attention being paid to linking low-income families to jobs, improved accessibility and mobility are particularly important.

Techniques for Improving Transit Access-Shifting location of employment and housing centers within a region can render once-useful transit service obsolete. These changes have encouraged many cities across the country to rethink and improve transit access. Two general ways in which transit access can be improved are by expanding transit supply through construction or service improvements, and focusing development around existing transit (transit-oriented development).

Microscale Urban design Factors

Aspects of the built environment such as building orientation, street connectivity and design, and building design all contribute to the relative friendliness of that area to pedestrians and bicyclists, and to the general aesthetic appeal of an area. Together, these are often referred to as "microscale" urban design factors small-scale elements that affect the safety, convenience, and desirability of living and working in areas of higher density and of using transit and nonmotorized modes of transportation. These design factors affect travel mode choice. In areas that do not include adequate bicycle and pedestrian facilities (sidewalks, bike lanes, and crosswalks), people are more hesitant to travel by foot or bike. By increasing the relative desirability of walking compared with driving, urban design factors can encourage more walking or bicycling trips. Reductions in vehicle travel and emissions can occur if walking and bicycling trips replace vehicle trips.

Conclusion

There is ample evidence that the built environment matters to communities not just for social and economic reasons, but also for environmental reasons of national concern. Issues related to our built environment are growing in importance and, if left unaddressed, will make it difficult to meet our nation's environmental goals. Fortunately, communities, regions, and states are starting to find ways to expand that achieve better economic, community, and environmental outcomes. The need of the hour is to continue building knowledge about the relationships between land use, transportation, and the environment as it supports our nation in meeting its environmental and human health goals.

References

1. Our built and natural environments - A Technical Review of the Interactions between Land Use, Transportation, and Environmental Quality

2. Concise Environmental Engineering by Dawei Han