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Monday, 5 September 2011

Urban Metabolic Growth

Mohammed Makki and Pavlos Schizas


Metabolic systems have been extensively studied within a biological context throughout history. However, it is only recently that metabolic systems have been researched and related to different fields. The contribution that a metabolic system, as a model, has on urban development is to ensure that the flow of energy is continuous throughout the system, where all the components that make up the system are interdependent. In other words, the backbone of the city heavily relies on allocating the natural resources that will sustain it from the onset. In modern day planning, there is a lack of consciousness in considering the availability of these natural resources and their significance in dictating urban development and growth. Ancient cities on the other hand do not seem to have the flaws that modern day cities have; these ‘evolving’ cities grew with respect to functionality and the location of resources. Despite the many paradigms that ancient evolving cities offer, modern day planners seem to overlook these examples. New research into urban metabolic growth in cities, presented here, aims to design two scenarios of metabolic urban development placed in two regions with different extreme climatic conditions, using planned cities and evolved cities as case studies to help govern the different elements that make up the cities’ fabric. Different tools and methodologies are utilised to help achieve two different scenarios that are based on the same metabolic model.


Research into urban metabolic growth begins with an analysis of the qualities that differentiate planned cities from those that evolve unplanned. To start, the planned city relies heavily on predictability. Planners must predict how many people will populate the city, the simultaneous growth of different sub-centres and in what manner the developers will implement the original plans. However, it is merely impossible for anyone to predict the expected popula¬tion of a city. The city of Brasilia, Brazil was predicted to accommodate 500,000 people, however it eventually grew to 2 million, pushing the city limits outside the boundaries of the topography for which it was originally intended. When creating a planned city, the planner must also control the rate by which the city grows. In the example of Milton Keynes, United Kingdom, the simple fact that one shopping centre grew faster than the rest had a vast negative effect on the city; retailers that were spread throughout the city could not sustain themselves, and consequently, a mono-¬centric city emerged. The analyses of several planned cities lead to a straightforward and vital conclusion: there is not any one street network that can be considered uniform and/or global enough to be applied to any site, regardless of topography or climate. The modern consensus is that the gridded street network has become the most efficient. This is completely false; the single advantage of gridded networks is a lack of congestion. Due to several routes to any destination, congestion is very rarely an issue. However, the disadvantage of this is that there are many streets that are very rarely used, leaving certain neighbourhoods ‘forgotten.’ It is within these neighbourhoods that crime is at its peak. Evolved cities on the other hand are much more culturally rich and have a high-functioning, topography-based street network. Nonetheless, it is difficult to come to a conclusion that is com¬pletely preferential towards evolved cities. This is due in good part to the variety of cultures that settle within them. The overlap of cultural neighbourhoods, each with their own unique identities and specific spatial and social requirements has given evolved cities their character. Thus, to simulate an evolved city seems impractical; to try and replicate a system that has evolved through several millennia is impossible. The logical solution seems to be an optimal balance be¬tween planned cities and those that have evolved; in other words, ‘”planning” an “evolving” city.’

Site Selection

Two test cases, one in Ningxia, north-central China, and another near Lake Argyle, northwest Australia, show the implications of a system designed through metabolic growth, and their combination within an urban environment. The common characteristic of these test cases is the area’s arid soil. However, the climatic conditions and energy and water consumption are extremely different; northern China faces cold dry winters while in Western Australia the climate is extremely hot during the summer periods.
Water resources are extremely essential for the nourishment of a developing city. The two scenarios include the indication of potential locations for reservoirs, with the help of digital fluid-simulating tools. The positions of the reservoirs allocate the paths for the irrigation systems, which will in turn inform the locations of the agricultural fields. The reservoir capacity also determines the size of the potential agricultural land, the qualitative properties of the crops as well as the population that can be sustained.

Integral Design Solutions

Through the process of expansion of superblocks along the topography some additional rules are introduced, which create variations in the density and organisation of the blocks. Three types of hierarchies are introduced in order to organise the urban space with the qualitative properties of the mix of uses within the city, and to avoid the crucial disadvantage of Modernist cities, which were completely function-dependent. Therefore, according to the size of each block, superblocks are organised into blocks of low-, medium- and high-energy demands, which in turn will acquire additional volume depending on each block’s specific needs. The volume added to the blocks is organised in such a way that the levels where people circulate around the city are incorporated within the built environment. The varied topography generates an interplay between building and landscape, often blurring the boundary between architecture and ground.

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