Making urban stormwater management more sustainable. A case study of Tallinn, Estonia

Abstract: The concept of sustainable urban drainage systems (SuDS) is increasingly recognised as a valuable approach to flood risk mitigation and urban landscape planning. Many European cities are considering integrating SuDS features to their stormwater management practices. More frequent weather events and water quality issues have emerged among the main drivers to advance the discussion on innovative ways to handle stormwater, especially in urban environments where the proportion of impervious surfaces significantly alters natural drainage patterns. Due to the relative novelty of the SuDS scheme, promoters of its components struggle with uncertainties and reluctance to change of key actors involved in making decisions about stormwater management. In this context, this thesis intends to reveal some key conditions that are necessary for the implementation of SuDS, by focusing on the planning process of stormwater management taking Tallinn city as a case study. It highlights opportunities but also key barriers that must be addressed to include SuDS into the urban landscape and planning decisions. The methodology of the research project includes a literature review on the SuDS concept, as well as an overview of the stormwater regulatory environment in Tallinn that helps put the SuDS adoption in context. To address its first objective, this research borrowed elements from theories of innovation diffusion and technology acceptance to investigate how perceptions of SuDS techniques’ attributes influence decision-makers’ attitudes towards their adoption as well as the determinants driving adoption in the case of Tallinn. A key feature of this first research objective was a survey conducted among stormwater planners, engineers and other relevant stakeholders. The survey results showed that a favourable perception of SuDS usefulness, ease of use, and benefits on the stakeholders’ side is likely to support and favour its adoption. While perceived insufficient resources could negatively influence intention toward adoption. Other relevant findings include some of the most significant barriers that currently hinder SuDS implementation. Furthermore, the study investigated whether a proposed geospatial approach could help detect flood susceptible areas at the city scale. To validate the method, a comparison was performed with prior flood points. From the obtained results and analysis, a few flood-prone locations were selected as potential SuDS sites. This led to the third objective of the research, which was to demonstrate the usefulness of a conceived planning method to help decision-makers select possible SuDS solutions depending on the site’s characteristics, SuDS benefits to prioritise and local preferences. Results from both approaches are promising as early stage, first assessment tools in SuDS planning practice which can be applied in order to first find suitable SuDS locations and then identify site-specific SuDS measures to address stormwater challenges. Based on the findings and valuable information included in this thesis, proponents of SuDS techniques will be better prepared to foster diffusion of these strategies at the city level. Recommendations for policy measures as well as suggestions for future research are provided as well. This thesis contributes to methodology, theory and practice, decision-making and policy studies.