M.Sc. Outi Tahvonen will defend dissertation Scalable green infrastructure and the water, vegetation and soil system. Scaling up from Finnish domestic gardens on Friday 25 October 2019
Opponent: D.Sc. Adjunct professor Tapio Katko, Tampere University
Kustos: Prof. Juanjo Galán Vivas
The ‘urban green’ concept should be considered in the context of multi-scalar green infrastructure (GI) designed to face the complex challenges of contemporary cities. GI is a spatial network that includes all urban greenspaces and penetrates all land-use categories regardless of their primary function. The main components of urban GI are water, soil and vegetation. Urbanisation and the concomitant increase in impervious surfaces decrease the soil’s access to sunlight and precipitation, reducing the potential for site-scale vegetation growth and generating runoff that demands special attention to stormwater management. Impervious coverage defines the extent of soil disconnected form GI. However, water, vegetation, and soil can be integrated as the core system of GI that exists throughout urban landscapes.
This dissertation focuses on the multi-scalar GI of one land-use category, low-density housing (LDH) in Finland. The aims are to study the role of private domestic gardens in LDH as part of the GI and to improve the potential of these gardens to more effectively support city-scale GI and the generation of multiple ecosystem services. LDH can support city and regional ecological connections and functions as the proportion of non-sealed surfaces is relatively higher than in other urban land uses. However, LDH is typically comprised of many plots, each with a separate owner, making the achievement of this goal difficult with conventional planning tools. The multifunctional and spatial nature of private gardens in LDH areas was studied via literature review, followed by a two-year experiment in a test field to study the functioning of the GI’s core system through the concept of bioretention. An iterative design process to improve the performance of private gardens on the plot, block and neighbourhood scales used a variation of the research by design method.
The results provide knowledge for urban planning, garden design and landscape construction that work mainly at different scales of GI. For urban planners the results formulate a check-list to recognize the garden scale multifunctionality in planning process of LDH and criteria for multi-scalar and hierarchical design process for scalable GI. For designers this dissertation proposes improved and integrative design process to functionally combine vegetation and stormwater management at plot scale. For the needs of practical landscape construction in Finland it develops construction details and material specifications of bioretention.
The results promote the integration of stormwater management and vegetation and the application of the GI’s core system. Designers’ knowledge of the core principles allows them to adaptively integrate stormwater management and vegetation with soil throughout the garden space. In addition, the continuous character of the GI’s core system relates to the idea of grey and green continuum to provide garden-scale microhabitats and benefit from sealed surfaces for the needs of vegetation. In turn, this garden-based biophysical environment may enhance GI at the block and neighbourhood scales and, thereby, the ecological network of an entire city.
The dissertation notice and the published dissertation are placed for public display at Väre (Otaniementie 14), close to the Info Desk, at least 10 days before the defence date.
Link to audience etiquette and dress code of the public defence (into.aalto.fi)