Tracing Flows of Water, Energy, and Waste Through an Idealized Water Distribution Network Using an Urban Metabolism Based Approach
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‘Urban Metabolism’ (UM) is a well-established concept based on the parallels between the metabolisms’ of ecosystems and cities. These parallels consist of the intake, storage, and transformation of materials and energy, and the creation and output of wastes. These traits, which suggest cities possess a metabolism similar to ecosystems, also exist within water distribution systems (WDSs). Four common areas of UM assessments include: the evaluation of environmental sustainability indicators; greenhouse gas accounting; numerical models for the assessment of metabolic flows; and design and decision support tools. These applications show promising opportunities if applied to WDSs, and therefore a novel framework based on UM was developed specifically for the assessment of WDSs. This framework was tested on a water distribution network via three experiments. Experiment 1 utilized factorial design to systematically assess predominate network parameters (water demand, static lift, and pipe roughness). Experiments 2 and 3 studied the effects of two network management strategies (water conservation and pipe replacement scheduling) as well as the effects of static lift and pipe roughness in the presence of these strategies. The results were reported in terms of four metabolic flows: water, operational energy (O/E), embodied energy (E/E), and greenhouse gases (GHGs). Experiment 1 showed that individual increases in water demand, pipe roughness, or static lift, all led to decreases in network pressures and reductions in leakage volume. Experiments 2 and 3 demonstrated increases to leakage volumes and decreases in per capita GHG emissions in the presence of water conservation measures, and decreases in leakage volumes and increases in O/E transmission efficiency in the presence of pipe replacement programs. Experiments 2 and 3 also demonstrated a reduction in network pressures, and a resulting reduction in leakage volumes, due to additional static lift and pipe roughness. Recommendations for future work were made in four specific areas: (1) the expansion of pre-established metabolic flows, (2) the further study of the effects of pressure management under the scenarios studied, (3) the consideration of other urban systems which may benefit from the application of an UM-based assessment, and (4) the assessment of non-hypothetical WDSs using the developed framework.