Ecological Reclamation of Distressed Urban Fabric through Open and Green Space Networks to Enhance the Urban Vitality Based on Graph Theory and Gravity Models (Case of District 9, Tehran)

Ecological Reclamation of distressed urban Fabric through Open and Green space Networks to Enhance the Urban Vitality Based on Graph theory and Gravity Models, the Case of District 9, Tehran
Authors
Masoomeh Mohseni Fard Naghani1, Mohammad Reza Masnavi2 , Lobat Zebardast3
1. MSc. of Environmental Design, Graduate Faculty of Environment University of Tehran, Iran
m.mohseni9190@gmail.com
2. Professor of Environmental Design, Graduate Faculty of Environment, University of Tehran, Iran
3. Assistant Professor of Environmental Planning Management, Graduate Faculty of Environment, University of Tehran, Iran, lzebardast@ut.ac.ir
Abstract
Introduction
Many metropolitan areas face large urban decay and distressed areas within the city fabric. The rapid growth and unleashed urban development have led to ecological transformation and landscape fragmentation during the recent decades. These resulted in the damages to the structure and function of the urban green/open spaces especially in urban fabrics; and affected the form, function and hence sustainability of urban systems. In some metropolitan areas, the driving forces for the sustainable development and improvement of the physical structures of urban areas faced great challenges and deficiency in recent decades. The inner city or central neighborhoods like any other ecosystem will change and in some cases are losing their livability and quality of life during the time. This is due to the rapid unsustainable development and lack of proper urban open/green spaces which are essential for the residents’ quality of life. The process has consequently, turned into the neighborhoods’ ecological and environmental deficiency, and more decays in urban fabric. These are observed to be true in some part of Tehran city. The fundamental changes in the Tehran urban fabrics are seen through fragmentation of green patches and open spaces. Some researchers have suggested that the solution to this problem is to change the attitudes of planners to create or strengthen urban green infrastructures systems. Therefore, this paper utilizes the Graph theory and Gravity model, for the analyses of green space network. These, provide powerful tools and methods for analyzing and optimizing complex systems and evaluating the quality and quantity of urban green spaces, as well as developing efficient ecological landscape solutions for the efficiency, connectivity and continuity of the green space networks across the district 9 neighborhood.
Materials and Methods
In this research, the district 9, Tehran city is investigated as the case study. District 9 is one of the 22 districts of Tehran with an overall area of 1966 ha, which accounts for 2.9% of Tehran's total area. The urban landscape structural elements in urban regions include Kan river- valley in the west district which is among the most prominent structural elements of the urban landscape, and a series of small – medium green spaces. The urban landscape context in district 9 constitutes of dense, fine-grained, impermeable constructed surfaces. Landscape structural spaces include private green spaces, public green spaces, brownfield spaces renovation reserved lands. Other structural elements such as faults, high pressure power lines and accessing network are considered potential for the creation of green corridors in the area. Through review of the literature the research, is aimed at identifying and analyzing the urban green space network based on the ecological landscape design framework.
By acquiring The land use map for the district 9, different information layers of the natural and artificial features were prepared including layers of river - valleys and watercourses, canal network, access network, fault, high pressure power lines, green areas, urban development lands and reserved lands for extracted, the overlapping layers and synthesis of data landscape elements, ecological network in district 9 was developed. First, at the macro level, the ecological effect of adjacent green spaces on each other in the distressed urban fabrics was calculated and variety of alternatives were presented to develop the most efficient green network in the distressed fabrics of district 9. At the micro level, the optimal connection route among the available routes were determined using the least cost route function. Weighted cost analysis for each node was performed separately by weighted cost analysis in GIS software. Subsequently, it was selected with the help of continuity indices in optimal network graph theory to develop green spaces in the distressed urban fabrics of district.
The interaction between the nodes is evaluated using the traction model. The interaction is calculated using the following formula:



G_ab=(N_a N_b)/(D_ab^2 )=((〖∑▒L)〗^2 LN(S_a S_b))/(L_ab^2 P_a P_b )
So that Gab interaction between nodes a, and b, Na and Nb are the corresponding weights, and Dab is the normalized cumulative impedance of the corridor between a, and b. Lab is the cumulative impedance of the corridor L between nodes a, and b, ΣL is the sum of the cumulative impedance of the corridor between nodes.
Discussion
The results suggest the greater the area of cross-spaces and the smaller the distance between them, the greater the ecological effect of cross-spaces. By calculating the amount of interaction between the spaces and prioritizing the links, the ecological network pattern in district 9, Tehran can be developed based on graph theory and gravity model. Then, alternatives are in the form of four proposed connection patterns. By comparing these connection patterns and network, the alternative 3 (Beckman Model) found to be the most efficient option for developing green space network for ecological reclamation, having 36 spaces and 37 links to improve continuity and achieve vitality in the distressed urban fabrics of district 9, Tehran. Figure 1 shows the alternative 3 (Beckman Model) based on graph theory and gravity model.
Figure 1.The alternative3 (Beckman Model) in district 9, Tehran based on graph theory and gravity model.


Some of the reasons for choosing this model are as follows:
It can generalized and can be connected to the open and green spaces in adjacent areas in a repeatable pattern.
The relative cost and number of connections compared to the other two models is such that it is responsive to users on the one hand, and responsive to green connections in the ecological network on the other hand.
The project can improve the spaces and network corridor features by applying ecological principles such as maintaining the integrity and cohesion of the ecological landscape in distressed urban fabrics, which may help in strengthening the corridors and urban green infrastructure.

Conclusion
Many cities and urban areas are suffering from the expansion of distressed urban fabric in their central cores; these have led to the lack of green areas and open spaces which are essential for the urban sustainability and vitality. In this study, using concepts in graph theory and gravity modelling as well as cost analysis, the Beckman model was selected as the most efficient model in analyses and application of alternative solution in district 9 for connecting green and open spaces among four categories of connection between spaces. Each green/open spaces network will be designed according to the planner strategy, location, opportunities and constraints, taking into the account the ecological design principles of the site, as well as improving the quality of life in the distressed urban fabrics.
Keywords: Ecological Reclamation, Distressed urban fabrics, Green space ecological network, Graph theory and Gravity model; District 9 Tehran.
Main Subjects
Landscape planning and design