The impact of urban sprawl and Solutions

abstract
 
With the development of economy, ordinary people also have the ability to move to the suburbs, which aggravates the further expansion of population and urban space. Urban sprawl began to encroach on forests and farmland, and also brought about the impact on urban environment, transportation and other aspects. Urban sprawl, as a bad phenomenon of urban spatial expansion, has brought many negative benefits, such as economy, environment and society, which has aroused widespread social concern. The urban sprawl of this subject has a certain negative impact on all aspects of the city, and puts forward relevant suggestions, hoping to help solve this problem

 Key words: urban sprawl; negative impact; Solutions
 



1. Introduction
 
1.1 concept connotation of urban sprawl
 
Urban sprawl is a complex system related to urban planning, environmental science, sociology and aesthetics, which can be defined differently from different perspectives. After collecting various explanations of urban sprawl, this paper interprets urban sprawl as follows: urban sprawl is a phenomenon in the process of urban development, which is a process of urban sprawl from the central city to the suburb and edge of the city. In the process of diffusion, wetland, farmland and forest are transformed into residential area and commercial area, and the dependence of society on household cars is significantly increased.
  
1.2. Historical overview of urban sprawl

Just like the development of many things, urban expansion is a long process. In his book a brief history of urban sprawl, Robert Brugman divides the history of urban sprawl into four stages. The early urban sprawl, the urban sprawl during the prosperity period of World War I and World War II, the urban sprawl during the rapid development period after World War II and the urban sprawl since the 1970s.
 
The first stage. The early urban sprawl refers to two years ago when there was just a city. Both the city of Babylon and the city in the south of Mesopotamia have obvious characteristics of an ancient city. By the time of ancient Rome, the population of Roman city had reached one million. Within the walls of these cities, there are dense streets and crowded buildings, so the rich build elegant villas and palaces in the suburbs or seaside outside Rome, which is the bud of urban sprawl.
 
The second stage. During World War I and World War II, mainly in the early 20th century, the outward spread of population and Commerce began to become apparent. By the 1920s, in northern Europe and the United States, the trend of migration to the outskirts of cities was no longer limited to the rich and powerful, but had become a popular movement. In London, for example, thousands of low-income families can also move from the crowded city center to the multi family houses and independent houses on the outskirts of the city. With the migration of living population, all kinds of industries are moving out of the city. During the decade from 1921 to 1931, the population of London increased by only 10%, but the land area for urban development increased by 200%. Large industrial centers rose rapidly along the main road out of the city. At this time, the city spread in other developed countries, such as Hamburg in Germany and Stockholm in Sweden. Some big cities in the United States, such as New York, are expanding more and faster than those from European cities, because the number of residents who have the ability to move outward to the suburbs exceeds the number of people who have moved from rural areas to urban centers.
 
The third stage. The rapid development period of urban sprawl after World War II. If there are many similarities between urban sprawl in Europe and the United States in the second stage and the first 40 years of the 20th century, then there are significant differences between urban sprawl in the United States and Europe after the Second World War. The urban sprawl in America is more obvious than that in Europe. The United States has experienced a huge birth peak, unprecedented affluence and rapid population growth. As a result, the urban sprawl has intensified.
 
The fourth stage. In the last decades of the 20th century, all cities in the world have experienced tremendous growth in population and land area. Today, the largest urban areas, such as Beijing, Shanghai, Tokyo, Yokohama, New York and Mexico, have a population of more than 20 million, and the city has spread across a large area, including highways, shopping centers, industrial parks, housing land, airports and many previously separate urban entities. In the rich industrialized countries, because the traditional commercial and industrial functions of the central city have moved to the edge of the city, quite a lot of cities have transferred the inner circle of the city to the outside in some aspects. At the same time, the central city and the area close to the center of the city have become an economic area with increasing affluent residents and advanced and expensive services.
  
1.3 research significance

1.3.1 theoretical value of subject research
 
With the development of the society, the economic strength of the city is increasing, and the urban system is becoming more and more perfect. But at the same time, in the process of urbanization, various problems and contradictions are increasingly prominent. As a development stage of urbanization, urban sprawl will bring serious environmental problems, but also many sociological problems. The phenomenon of disordered expansion and rapid spread of cities leads to the consumption and waste of agricultural land, water resources and other resources. The disordered spread of urbanization is changing the social life and living space of urban residents. It is necessary and valuable to analyze the impact of urban sprawl on economic, social life, especially on the environment, and put forward constructive suggestions, no matter for the study of urban sociology or the theory of urban sustainable development.
  
2. Negative impact of urban sprawl
 
2.1 waste of resources
 
2.1.1 waste of cultivated land resources
 
The surrounding land of many cities is mostly agricultural land with fertile soil and high productivity. In the process of urban sprawl, the market will allocate land to the land developers and bidders who can bring the most profit return, while the long-term production potential, ecological benefits and social benefits of land resources will be ignored.
 
Secondly, the more developed traffic system and traffic network is one of the necessary conditions to promote the urban sprawl. The relevant data shows that the construction of traffic network at all levels of roads, railways, airports and other traffic networks mainly occupy cultivated land, especially the high-quality cultivated land in the suburbs. Therefore, the urban sprawl will inevitably lead to the loss of high-quality cultivated land and aggravate the contradiction between the supply and demand of cultivated land.
 
2.1.2. Waste of energy
 
As a result of the urban sprawl, the urban boundary is more and more far away from the urban center, and the suburban development is more and more inseparable from the expressway, which means that people's average travel distance for work, shopping, school, entertainment and other activities is also more and more far away, and their dependence on private cars is more and more deep. Increased travel directly translates into increased energy consumption. The growth rate of private cars is increasing year by year, and the original roads are gradually blocked by more and more cars. Therefore, the construction of new roads and the reconstruction of old roads have become very urgent, but the new roads make more land development, and the new land development will bring the traffic congestion back to the original level of congestion again, and then demand to expand the traffic capacity again. Although the completion of the new road solves the current local congestion problem, in the long run, it makes the remote suburbs further expand. The result is heavy consumption of land and oil.
 
2.2 environmental pollution
 
2.2.1 unbalanced access of groundwater

Urban groundwater is not only an important factor to maintain the stability of the ecological environment system, but also an important water source to maintain social and economic development. With the acceleration of urbanization, the rapid spread of the city has a huge impact on the spatial structure and ecological resources¹. The new area development and infrastructure construction brought about by the urban spread mostly need to cover the hard ground surface, which inevitably increases the surface runoff, reduces the infiltration and rainfall infiltration supply of groundwater. The decrease of seepage flow and excessive domestic water consumption of suburban residents seriously consumed groundwater source 3. And when the urban sprawl is in the design and construction of underground parking lot, underground warehouse and underground commercial street, it is often necessary to dredge the drainage in the process of underground space development, so as to affect the storage of underground water resources. The existing research results show that the development of underground space will change the hydraulic connection between surface water and groundwater, destroy or change the regulation and storage capacity of groundwater resources.The urban life range is expanding, and its life style not only affects the supply of groundwater, but also affects the quality of groundwater
 
The increase of urban population leads to the increase of garbage volume, and about 90% of domestic garbage is landfilled. The landfill waste forms harmful leaching liquid and gas through its own decomposition, fermentation and rainfall leaching, which pollutes the groundwater. Relevant scholars have shown that wastewater discharge, landfill and pipeline leakage affect the groundwater quality; the use of urban traffic road salt, turf fertilization, pesticide spraying and construction machinery oil leakage, wastewater and waste slurry generated by underground space construction, It also poses a threat to the safety of groundwater quality².
 
 2.2.2 wetland degradation
 
Wetland is a unique ecosystem with multiple functions on the earth. It not only has rich resources, but also has a huge function of environmental regulation. All kinds of wetlands play an important role in regulating climate, preserving water source, slowing down flood, purifying environment, protecting biodiversity and providing production and living resources for human beings. But urban sprawl takes up a lot of developed or undeveloped land at the expense of land, most of which are high-quality agricultural land around the city. With the continuous reduction of cultivated land and the rapid growth of population, human demand for material, including living space and food supply is also increasing. This promotes the continuous development of agriculture, animal husbandry, industry and related service industries, the continuous demand for food from land, the construction of farmland and water conservancy, resulting in the reduction of wetland supply water sources, vegetation degradation, coupled with the over exploitation of groundwater and sewage pollution, and ultimately lead to wetland degradation.
 
2.3 not conducive to social equity and solidarity
 
Compared with the efficient and compact development type city, the inefficient and sprawling development type city has larger space, worse traffic conditions, and greatly increased the travel time of residents, which correspondingly reduced the leisure and entertainment time of people. Secondly, the spread community layout increases the distance between neighbors, and reduces the harmonious atmosphere of the community to a certain extent. Third, the spread of development has also brought about social injustice and intensified the differentiation of social income levels. Urban sprawl makes people travel more dependent on cars, which is very beneficial to high-income groups to a great extent, while low-income groups may not be able to afford expensive transportation costs, thus aggravating urban social conflict³s.
 
2.4. Hinder the healthy development of the city
 
On the impact of urban sprawl on urban development, although there are still some controversies in the research field, for example, some scholars believe that urban sprawl can alleviate the pressure of reducing urban traffic, employment, housing and other pressures to a certain extent, but researchers generally believe that urban sprawl expansion consumes more resources and funds than compact development, intensifies urban social isolation, and affects urban social harmony. Urban development needs to consume a lot of economic cost, which is one of the important factors to increase the economic cost of urban development.
 
Urban sprawl has increased the government's public investment in roads, sewers, street lights and other infrastructure, making the government have to strengthen infrastructure construction, such as road construction, municipal facilities construction, etc. However, on the one hand, the vacancy of the original municipal service facilities in the central area of the city is not fully utilized. On the other hand, a large number of social resources flow to the new area, and the repeated construction of municipal facilities such as roads and sewers wastes social resources. In addition, with the migration of the middle class and the blue collar, as well as the transfer of industries and jobs from the central city, the employment opportunities in the central area are reduced, the spatial distribution of jobs and population is not matched, and the tax revenue in the central area is seriously reduced, followed by the further decline of the inner city. All of these make the city unable to develop healthily.
 
3. Solutions to urban sprawl
 
3.1 change the concept of urban development

3.1.1 New Urbanism
 
The new urbanism advocates that the community should be full of vitality, walkable, compact and mixed use, and the layout of the building should be re planned, which can combine the natural environment and the community into a harmonious whole. According to the new urbanists, there are separate goals for decentralized low-income people and fair housing sharing, but they are intertwined at the same time. Fundamentally speaking, they share the same regional goals. Establish a multi-level and mixed housing system in the region, increase the affordable housing that low-income people have the ability to buy and distribute reasonably, so as to disperse low-income people, provide them with more employment opportunities, reduce dropout, reduce crime and other social problems⁴. In addition, the boundary of urban growth should be determined so as to provide a reasonable scale for the construction of more compact communities, to revive the declining areas, and to make full use of the investment in infrastructure services, so as to achieve the purpose of protecting the regional environment and saving resources.

The core ideas of new urbanism are as follows: first, attach importance to regional planning, and emphasize to view and solve problems from the perspective of regional integration; second, people-oriented, and emphasize to build a pleasant environment and support for human social life; third, respect history and nature, and emphasize the harmony between planning and nature, humanity and historical environment.
 
3.1-2 growth management

In the 1970s, the developed countries in Europe and the United States carried out effective management on many problems in the process of urban growth, including land reduction, low-density development, traffic congestion and environmental pollution, which were widely mentioned as the growth management strategy guided by compact development, filling development and movable neighborhood⁵.

Growth management refers to the government's use of various traditional and evolving technologies, tools, plans and activities to guide the local land use patterns, including the way, speed and nature of development, so as to keep the development and protection, and the development and infrastructure of various forms in a synchronous manner, The dynamic balance between the demand for public services generated by growth and the financial supply to meet these demands, as well as between progress and equity. Growth management attempts to use planning, policies and regulations to influence the distribution of development projects in the planning area. Its development goal is to carry out new development under the conditions of protecting community characteristics, environmental resources, opening up space and restricting new infrastructure investment.In practice, in order to achieve these goals, the community has created a set of relevant measures, including annual building restrictions, delineation of urban growth boundaries, innovative zoning planning technology, land protection projects and adaptation to public utility regulations. Through growth management, many cities in the United States have effectively controlled urban growth, especially many drawbacks of urban sprawl, It improves the efficiency of urban development quality.
 
3.1.3 smart growth
 
Smart growth is mainly aimed at the disordered spread of suburbs and the decline of central cities. With local governments as implementers, it can achieve the goal of urban sprawl control by protecting agricultural land, reviving the existing communities of cities, maintaining the affordability of housing, providing a variety of transportation options and other means. It has sustainable development and operability.Smart growth measures are usually summed up in seven aspects: protecting open space; delimiting boundaries to limit the outward expansion of development;
 
Compact development and mixed use of land; walkable and public transport; renewal of old town centers, suburbs and close to failure business districts; development of reliable public transport to reduce dependence on private cars and support other development models; regional planning coordination: fair distribution of public finance and fair burden of taxes. American empirical research shows that smart growth model can greatly reduce the government's investment in infrastructure⁶.
 
3.2 adhere to the scientific and public participation in the decision-making process of urban development
 
3.2.1 scientificity of urban development decision-making process
 
First of all, we should abandon the old idea that urban development is mainly economic growth and material expansion, and that urban social development, urban environmental protection and governance should be put in a secondary position. We should also eliminate the old idea that urban management should be understood as the behavior of a single government subject, and that administrative behavior should be based on the traditional bureaucratic system. We should emphasize that urban development is the integration of economy, society and environment and the development with quality, and that urban management is a new concept of governance with the participation of government, enterprises and society⁷. Secondly, as a complex system of multi-level, multi variable and multi factor agglomeration, the decision-making of urban development is not simply determined by several people or a department of the government, but involves many disciplines such as economics, sociology, demography, ecology, architecture, law, and many related functional departments of the government, We should give full play to the role of all kinds of experts in urban government management, and give full play to the advantages of coordination and cooperation among various departments.
 
3.2.2 public participation in urban development decision-making process
 
The scientific decision-making of urban development should come from the investigation and research of professionals and the feedback to the real life situation of the public. The public should not be the object of urban management, but the leader and beneficiary of urban management. As the driving force of strengthening urban development management, the public should directly participate in the management decision-making and implementation supervision of urban sustainable development.
 
In the process of urban development, in order to make a better decision before the implementation of any major project, the government or relevant project proponent should consult the representative public in an open and transparent manner at an early time to understand the needs of residents. Make it easy for the public to obtain materials and information, use the knowledge and skills of residents, reach consensus through communication, cooperate with each other, build trust, reduce confrontation, let the public participate in the project, and improve the overall social benefits⁸.
 
3.3 strengthen urban planning and design and environmental management

3.3.1 strengthen urban planning and design
 
At the beginning of urban planning and design, first of all, it is necessary to plan out whether the future development location should be developed. The planning should not only involve a local area or business center, but also a wide and comprehensive scale. The satellite technology can be used to take a picture of the whole planned area. By analyzing the basic information of soil properties, commercial facilities, population density, hillside, vegetation and so on, a reasonable urban spatial layout plan 9 can be designed. Secondly, in urban planning and design, to restore the traditional functions of the city, the development of residential areas must take into account all the needs of urban living⁹. Third, in urban planning and design, we should make full use of the existing urban infrastructure such as roads, bridges, sewers, etc., repair and maintain the facilities that can still be used, and reduce the repeated construction and excessive waste of infrastructure construction as much as possible. Fourth, and most importantly, the personnel in charge of planning and design should eliminate all interference, maintain political independence, not be influenced by the opinions of the government leaders, concentrate on urban development issues, and seriously and efficiently solve problems.
 
3.3.2 strengthen urban environmental management
 
Urban environment usually covers a wide range, including economic environment, social environment, ecological environment, etc¹⁰. The urban environment discussed in this paper is more from the aspect of ecological environment.
 
Strengthening the management of urban environment is an important support and guarantee for the comprehensive renovation planning of urban environmen¹¹t. In the process of urban environmental management, we should not only adhere to the implementation of effective environmental management system, but also strengthen the monitoring of environmental quality and the whole process of industrial pollution, through the daily standard responsibility system of urban environment and the assessment of the comprehensive treatment of urban environment, implement the overall control of main pollutant emissions according to the environmental function zoning, allocate the total control indicators to the source, and implement the emission permit system; Reform the environmental management system¹².
  
summary
 
Urban sprawl has caused negative effects on environment, resources, society and other aspects. The government should draw on advanced urban development theories and ideas in urban development planning, solve the environmental problems in the process of urban sprawl, adopt scientific and effective plans to actively carry out planning and management, and promote the healthy development of the city.


 
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