台北地區都市建設代謝作用物質流分析與能值評估

MATERIALS FLOW ANALYSIS AND EMERGY EVALUATION OF TAIPEI'S URBAN CONSTRUCTION

都市代謝作用係指維持都市居民生活及生產所需提供之物質，這些物質在生產及消費行為經轉換後再輸出或排放出都市的過程。近年來都市規模快速擴張，除加速其代謝作用物質的流動量，而其所產生的線性代謝作用模式更對環境產生極大之影響。本研究以台北地區公共工程（包括道路、橋樑、下水道、防洪、捷運工程）及建築工程等都市建設活動所產生的代謝作用物質（包括砂石、水泥、瀝青等建材資源及廢棄土）為研究對象，分析近二十年來台北地區都市建設代謝作用物質流動的趨勢。根據估算結果顯示台北地區都市建設代謝作用物質流動量主要以砂石資源為主（佔91%），且每年約產生3000萬噸的棄土量，其中以公共工程所佔比例最大。能值評估結果顯示，台北地區都市建設所使用之砂石、水泥、及瀝青，在總體生態經濟系統之貢獻雖因都市工程建設逐漸完成而減少，但仍佔極重要之份量。其中，尤以水泥為最。此外，廢棄土能值在廢棄物中之比例極高。為進一步探討台北地區都市開發建設行為對於自然、人文環境的影響，本文並建立整合都市建設、代謝作用及自然作用的永續性指標。分析結果顯示目前台北地區資源使用結構仍以都市建設活動為主，但已趨於平緩，且建材資源的使用效率已有明顯的提昇，不僅使每人擁有道路面積及污水下水道普及率提高，亦使淡水河嚴重污染程度降低。另一方面，土壤大量流失使淡水河輸沙量增加。在廢棄土方面，每年所產生的棄土量高達3000萬頓，約為台灣地區三分之一，且資源使用量亦高達1000萬頓，對地表是雙重的破壞，而回收再利用或回填的比例相當低，僅有500萬噸左右。未來除積極開發多樣性的砂石料源，建立健全的砂石資源市場供需調查機制，並有效的回收利用廢棄土，提高資源使用效率，解決砂石料源短缺的問題，且應以興建鋼骨結構物為主，以符合建築開發與環境共生共存的理念。

The metabolism of a city can be seen as the process of transforming all the materials and commodities for sustaining city's economic activity. The rapid urban growth has not only accelerated the material flows of urban metabolism; its linear pattern has also resulted in the adverse environmental effects. This paper attempts to apply urban metabolism concept to investigate Taipei area's urban sustainability due to urban construction. The material flows (sand and gravel, cement, asphalt, and construction waste) 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 during the past decade. As a result, the consumption of sand and gravel is approximately 90% of total construction material used, and the generation of construction waste in Taipei exceeds 30x 106 ton per annum. In order to evaluate the contributory value of material flows to the ecological economic system, emergy 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 emergy value of construction materials in Taipei is equivalent to 46% of total emergy use. Although the livability in Taipei has improved but 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 also is vital to the sustainable development of Taipei.