عنوان مقاله [English]
Fundamental changes in social, economical, and political institutions have caused rapid increase in urban population in recent decades. Unprecedented urbanization and prolonged growth of population not only have created large cities, but also they led to the formation of cities, changes in the size of them and their development in different sizes and shaping of informal settlements, advancing towards existing environmental spaces, natural resources, farmlands, and gardens surrounding them. Therefore, this trend has caused a lot of problems in different dimensions such as housing, unemployment, informal settlements; and inability of urban environments to make the problems due to rapid change such as inharmonious growth of city suburbs and influx of urban land use within that. The population of settlements in Tehran boundary has grown about 200 percent from 1986 to 2006 in Tehran metropolitan region, while in this period Tehran’s population has merely experienced 30 percent growth. As a consequent of these changes on the population, physical transformations have been much more in suburb of the city. This transition caused this area to face with many challenges which show the necessity of planning for Tehran limit line. In this paper, given the fact that urban greenbelt policies has successfully been implemented in different cities around the world, as a kind of planning for the suburbia and the restriction policy of urban growth, greenbelt policy with conservational development approach has considered for this limit boundary. With this in mind, the main aim of this article is to guide and control the growth of Tehran and other cities within its limit line through studying how to create greenbelt and defining a range of permissible operations in this area. Permissible operations in suggested greenbelt are generated through an integrated approach including four factors of conservation, facilities and infrastructures, agriculture and urban. For this aim, two questions are put forth in this research:
1) how can greenbelt be created in the fringe of Tehran metropolis? 2). whether the suggested greenbelt would be effective in guiding and managing the city growth or not? This study methodologically is a descriptive- analytical one. The used method in this research is Delphi together with overlaying spatial layers. In this process, first indicatorsof permitted functions were rated by Delphi method, then indicators were relocated in spaces and finally spatial layers were over-laid based on the coefficient of importance of indicators, in ARC GIS environment to reveal the zone of the performance in the limit situated in the greenbelt of Tehran metropolis. Analytical model in this research is in fact procedural definition for achieving to a zone entitled greenbelt with four functions including urban, conservation, agriculture, and infrastructure areas in Tehran limit line with the aim of management of urban development. The findings of analysis indicate that north and east zones of Tehran’s limit line, although agricultural acts and gardening are practiced there sporadically, are prior to theconservational and the agricultural functions since they are environmentally qualified; but south part of suburbia in addition to main farming function is suitable for urban and infrastructural developments. In this sense, combination of four performances can be seen in that part. Regarding to that, in suggested greenbelt, prioritization of zoning was based on preservation in conservation and development of agricultural activities. Moreover, suggested areas for urban development do not interfere with the other two and have completely taken into account environmental observations. Also, the degree of changesin the four performances levels in suggested greenbelt and the existing situation were compared. The difference was about 65 and 100 percent growth in the conservation and agriculture levels; while the increase of the level of urban and infrastructure zones was about 25 percent (with preference of the conservation of agricultural and other lands). Therefore, it can be concluded that greenbelt policy is an effective one among the polices of guiding and control of cities growth for Tehran urban growth management and protection of valuable lands of this area, based on integrated approach and intended functions in this approach. Under these circumstances, it is suggested to develop an organizational structure for guide and control the growth management in Tehran limit line in one hand and to codify the zoning rules and monitor its implementation by the intended institutions on the other hand. In addition, it is strongly recommended to do more researches on Tehran limit line at existing pathology and optimum management. It is also suggested to do more study on evaluation of the effects of the creation of green belt in the Tehran limit line by other authors.