Provisional Green Infrastructure in Indian Megacities: Assessing the Upscaling Potential of In-stream Interventions for Sustainable Urban Water Management

Abstract

The management of stormwater and wastewater is a critical challenge for urban sustainability, and one that is increasingly attended to by researchers and designers across a range of disciplines. Traditionally, water quality has been managed through large-scale, centrally managed infrastructure such as pipes, drains, and wastewater treatment facilities. Green infrastructure (GI) is an alternate approach that supplements these systems through decentralized nature-based solutions. This dissertation introduces a new type of GI, Provisional Green Infrastructure (PGI). PGI is posited as a speculative innovation typology for sustainable urban water management emerging from the Indian megacity, with important implications for other contexts. PGI is defined as “Informal nature-based retrofits to existing grey infrastructure networks for the purpose of improving water quality within highly unpredictable, space-constrained, and contaminated urban environments.” Throughout the research, PGI serves as a “boundary object” for grounding multiple lines of inquiry. Chapter 2 defines the PGI concept, and suggests its relevance for megacities characterized by a broad range of spatial, infrastructural and governance constraints. I situate PGI in the context of urban informality and introduce two distinct types of upscaling (spatial and organizational) as pathways for future diffusion. Chapter 3 draws on interviews and surveys to explore barriers to broader PGI adoption, identifying specific misalignments between innovators and Potential Future Adopters (PFA’s) using the Diffusion of Innovations (DOI) framework. It is suggested that additional efforts by innovators should be made to emphasize the simplicity and relative advantage of PGI to decision-makers. Chapter 4 establishes the efficacy of PGI designs for a range of important water quality parameters, and discusses the limitations on PGI performance in an in-stream context. PGI using both gravel and terracotta substrates both perform reasonably well for detaining or removing physical and biological contaminants, but show limited reductions of pathogens and Ammonia-N (for which there was an increase). KBOD5 removal rate was statistically significant for gravel substrate. TP removal was higher in terracotta substrate. Chapter 5 explores the potential for citywide impact using the Stormwater Management Model (SWMM 5) and discusses how various upscaling scenarios and variations in the spatial location and configuration of PGI’s may impact cumulative catchment-wide performance (including cost, water quality improvement, and issues of public access). The study is intended to be used as a model for future Decision Support Systems (DSS) for decision-makers by combining Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) along with a post-hoc sensitivity analysis to interpret the results given various weighting of input variables. The results suggest that upgradient dispersed configurations of PGI may be most advantageous in cases where the importance of public access and TSS capture is given more weight. Dispersed configurations of PGI performed better than centralized for reducing TP loading at downstream receiving waters and are higher ranked as advantageous when the importance of TP is given more weight. Citing the above as evidence-based design, the research concludes that PGI should not be viewed as a functional replacement for conventional wastewater treatment infrastructures, but rather as a supplementary stop-gap function in contexts where functional separation of wastewater and stormwater are unlikely to occur, or where existing large scale WWTP’s operate below their designed capacity.