Materials Flow Analysis and Emergy Evaluation of Taipei's Urban Construction
The metabolism of a city can be seen as the process of transforming all the materials and commodities for sustaining the city's economic activity. This paper attempts to incorporate resource and material flow analysis to investigate Taipei area's urban sustainability due to urban construction. The material flows (sand and gravel, cement, asphalt, and construction waste) during the past decade for constructing major urban engineering projects such as roads, bridge, MRT, flood prevention projects, storm drainage and sewerage pipes, and buildings are analyzed for Taipei metropolis. In order to evaluate the contributory value of material flows to the ecological economic system, emergy (spelled with an M; previously known as embodied energy) evaluation is incorporated in this research. A framework of indicators including categories of: (1) intensity of resource consumption; (2) inflow/outflow ratio; (3) urban livability; (4) efficiency of urban metabolism; and (5) emergy evaluation of urban metabolism is developed for measuring the effect of urban construction on Taipei's sustainability. The consumption of sand and gravel is approximately 90% of the total construction material used, and the generation of construction waste in Taipei exceeds 30×106 ton per annum. The emergy value of construction materials in Taipei is equivalent to 46% of total emergy use. Although the livability in Taipei has improved, the significant amount of construction waste remains an important environmental issue. The recycling and reuse of construction waste can not only create circular pattern of urban metabolism but is also vital to the sustainable development of Taipei.