Reshaping the urban water management paradigm: towards a new decision-support framework for the sustainable design of hybrid systems

大型集中式供水系统提供了普遍覆盖，并利用了规模经济优势，几十年来一直主导着全球的市政供水服务。加拿大的大多数城市都依赖单一的水源，蒙特利尔的88立方米/秒的污水处理设施，可能是世界上最大的流量能力，很好地体现了这一范式。然而，今天，许多城市污水系统以最大容量或超过最大容量运行，限制了城市发展并造成不利的环境影响。为了避免大规模的系统扩展成本，越来越多的人建议完全分散的污水系统（如化粪池）服务于新的城市发展，由于不适当的运行条件，可能会造成灾难性的长期环境和公共卫生影响。在这两个极端之间，中小型“卫星”污水系统可以纳入大型城市规划。事实上，为了支持城市水系统（UWS）的战略规划，需要重新审视集中式和完全分散式的模式，采用新的替代方案，多尺度的UWS方案，并需要新的分析方法和工具来指导设计未来可持续和有弹性的城市的决策。本研究考察了新型“混合”UWS配置的技术、经济、环境和社会潜力，即在混合规模下运行。为此目的，将发展未来情景分析、系统建模和综合评估工具的混合方法。将对魁省和安大略省现有的供水系统进行分析，以确定影响供水系统效率的城市化模式(1)提供供水服务的成本效益和规模经济；（ii）污水排放及合流污水渠溢流对环境的影响；（三）从不同用途和接触改善的水质中获得最大的社会和公共卫生效益（O1）。在魁北克南部的一个案例研究城市中，将根据可持续性的三个维度评估利益相关者和社区对未来UWS的偏好，形成为UWS发展提供信息的情景分析的基础（O2）。为满足案例研究城市未来系统容量需求，新的混合配置将使用废水处理和污水系统建模工具（O3）进行建模，并将使用将开发并集成到空间规划工具（O4）中的新的空间多标准决策分析框架，在可持续性方面与传统选择进行比较。这种高度跨学科的方法将增强UWS的科学稳健，创新的空间规划，具有克服技术锁定和路径依赖的潜力。提出这样一个新的UWS规划范式是创新的，这种管理模式的现场评估尚未在城市规模上实施，利益相关者的参与是具有挑战性的；然而，预期的社会、环境和经济效益是巨大的。

Large centralized systems, providing universal coverage and taking advantage of economies of scale, have dominated municipal water services worldwide for decades. Most cities in Canada rely on a single water source, and Montreal's 88-m3/s wastewater treatment facility, with probably the highest maximal flowrate capacity in the world, exemplifies this paradigm very well. Yet today, many municipal wastewater systems operate at maximum capacity or beyond, limiting urban development and causing adverse environmental impacts. To avoid large system expansion costs, fully decentralized wastewater systems (like septic tanks) are increasingly proposed to serve new urban developments, causing potentially disastrous long-term environmental and public health impacts due to inadequate operating conditions. Between both extremes, small and medium scale 'satellite' wastewater systems can be incorporated into large urban schemes. In fact, to support strategic planning of urban water systems (UWS), the centralized versus fully decentralized paradigm needs to be revisited with novel alternative, multiscale UWS options, and new analytical approaches and tools are needed to guide decision making in designing future sustainable and resilient cities. This study examines the technical, economic, environmental, and social potential of new 'hybrid' configurations of UWS, i.e., that operate at a mix of scales. To this end, a mixed methodology of future scenario analysis, system modelling and integrated assessment tools will be developed. An analysis of existing UWS across the provinces of Québec and Ontario will be performed to identify urbanisation patterns that affect UWS's efficiency in terms of (i) cost-effectiveness in delivering water services and economies of scale; (ii) environmental impacts from wastewater effluents and combined sewer overflows; and (iii) maximal social and public health benefits from different uses and exposure to improved water quality (O1). In a case study city located in Southern Quebec, stakeholder and community preferences for future UWS will be assessed according to the three dimensions of sustainability, forming the basis for a scenario analysis that informs UWS development (O2). New hybrid configurations to meet future system capacity needs in the case study city will be modelled using wastewater treatment and sewage system modelling tools (O3) and will be compared with traditional options in terms of sustainability using a new spatial multicriteria decision analysis framework that will be developed and integrated into a spatial planning tool (O4). This highly interdisciplinary approach will enhance scientifically robust, innovative spatial planning of UWS that has the potential to overcome technology lock-in and path-dependency. Proposing such a new UWS planning paradigm is innovative, field evaluations of such a management model have not yet been implemented at city scale and stakeholder engagement is challenging; yet, the expected social, environmental and economic benefits are huge.