Figure 2.8 A Sankey Diagram

Figure 2.8 A Sankey Diagram

Source: Author elaboration (Sebastian Moffatt). Note: A Sankey diagram is comprised of partitions, nodes, edges, and arrows. A partition represents the transitions or stages within the fl ow where transformations may occur. The nodes are the divisions within a partition; they represent processes or events that regulate or transform the quality of fl ows. Edges are the paths (or noodles) that emerge from nodes and that direct fl ows to nodes on the next partition. The width of the edges is proportional to the fl ow quantity. Arrows indicate fl ow direction.

lar to the metabolism of a living organism that consumes natural resources to stay alive. If Sankey diagrams are used to illustrate these nature-to-nature fl ows, they are referred to as meta diagrams. Flows of resources may be illustrated for individual developed sites or for whole cities. Flows are typically averaged over one year, although both the time period and the spatial scale may be selected to answer whatever questions are of the most interest.

Figure 2.9 provides an example of a meta diagram for water fl ows through a parcel (a house site) in New Delhi. The Sankey has fi ve preestablished partitions: sources, converters, demands, reconverters, and sinks. Converters and reconverters are general terms for the on-site urban infrastructure or appliances that store, convert, regulate, separate, process, or recycle any fl ow. A converter is on-site and upstream of all service demands, while a reconverter is on-site and downstream of at least one service demand. In the example shown, the majority of water fl owing through this parcel arrives as rain, about 60 percent of which passes directly through the site to be absorbed in the ground. The remaining rainwater is captured by the roof and stored in a cistern, from which it is mixed with a neighborhood groundwater system and used to supply many household needs. The greatest single use of freshwater is the cooling system. The diagram quickly reveals advanced looping systems: water from the kitchen and baths is reclaimed and used for toilet fl ushing, and water from the septic tank is reused for pipe irrigation.

Meta diagrams constructed at the parcel level, such as the one shown, may be summed to create a Sankey for a collection of parcels, the neighborhood, or a city. An example of a citywide meta diagram shows baseline water fl ows for Irvine, California, a community of 180,000 people south of Los Angeles (fi gure 2.10). The climate in Irvine is dry (13 inches of rain per year), and the city has developed one of the most complex and advanced water systems in the United States. The diagram provides all the key information on a single page.

Five Reasons for using meta diagrams in systems analysis and design

1. Understanding the whole picture. A meta diagram may be designed to convey quickly many aspects of a system to people of diverse

“ The built environment as a self-organizing system functions as a ‘dissipative structure’ requiring a continuous supply of available energy, material, and information necessary to produce and maintain its adaptive capacity and rejecting a continuous stream of degraded energy and waste back into the ecosystem (entropy).”

Source: Rees (2002: 253).