Stormwater management for highly urbanized areas in the tropics: Life cycle assessment of low impact development practices

Abstract

Within the contemporary view of stormwater management, introduced through integrated urban water management approaches (e.g., low impact development [LID]), there are several strategies that can be used in urban settlements to enhance sustainability. These strategies include the construction of runoff source controls and changes in development patterns. To understand the environmental trade-offs, the comparison of single LID devices using life cycle assessment (LCA) is spreading. However, assessing both LID practices and the urban catchment hydrological response is a less explored field - especially in regions under climate conditions other than the temperate urban areas where LID first emerged. In this context, this paper aims to assess the environmental impacts and the hydrological effects of applying LID practices in a highly urbanized area in the tropics. Using a settlement in Brazil as a case study, three projects were developed and assessed using a hybrid framework based on hydrological modeling and LCA. Even though the projects had different elements, their system function was the same: assure flood protection for rainfall events with a 2-year return period and for a 30-year service life. The business-as-usual scenario, entitled Scen.CONV, used a conventional urbanization and storm-sewer conventional drainage system (CDS), commonly known as gray infrastructure. The alternative scenario, entitled Scen.WELL, used a conventional urbanization and CDS associated with the use of the LID controls to disconnect the lots (infiltration wells). The last scenario, entitled Scen.LID, used LID controls to disconnect both lots and streets (infiltration swales and swale trenches, considered green infrastructure measures) integrated with changes in development patterns. The hydraulic-hydrologic results pointed out Scen.LID as the best alternative for flood protection (100% of runoff source control), followed by Scen.WELL (60% decrease in the peak flow compared to Scen.CONV). The LCA total results indicated Scen.LID as the scenario with lower life cycle impacts, and Scen.WELL as the most impactful. However, this capacity-based approach could not capture the hydrological benefits of Scen.WELL, which were addressed using a performance-based functional unit. Assessing potential impacts per managed stormwater volume, Scen.WELL's life cycle impacts were 51-65% lower than Scen.CONV, and Scen.LID's were 74-82% lower than Scen.CONV, both in all life cycle impact categories. This joint approach provides a new perspective to stormwater systems assessment, enhancing their hydrological benefits, without burden shifting.