Ecosystem services assessment of blue-green and grey infrastructure to support planning of sustainable and resilient cities.

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Theses / Dissertations
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Thesis discipline
Civil Engineering
Degree name
Doctor of Philosophy
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Journal Title
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Volume Title
Language
English
Date
2022
Authors
Nguyen, Thuy Thi
Abstract

Ecosystem services assessment and planning-support tools are evolving to become more widely used by city planners, designers and decision-makers in developing resilient and sustainable cities. Challenges in urban environments that need to be addressed are global population growth, urbanisation, physical and biological resource depletion, climate change impacts, and human well-being. These tools must have the capability to reflect the complex, multi-functional urban environment and quantify advantages and disadvantages of potential land use and/or blue-green-grey infrastructure changes in a spatially distributed manner. To provide solutions to these challenges the objectives of this research were: 1) parameterisation and refinement of the Land Utilisation and Capability Indicator (LUCI) in order to model urban ecosystem services (flood mitigation, carbon sequestration, water purification, habitat connectivity and evaporative cooling) in the Ōtākaro/Avon River catchment case study (i) in its current state and (ii) under different climate change scenarios to assess the effect of the selected blue-green infrastructure measures on urban ecosystem services; and 2) to apply the Urban Biophysical Environments and Technologies Simulator (UrbanBEATS) to determine the optimum sizes, density and locations of grey infrastructure - rainwater tanks - on water provisioning and flood mitigation under different climate change scenarios.

Three existing tools in LUCI, flood mitigation, carbon stocks and fluxes, and habitat connectivity were parameterised to reflect a New Zealand (NZ) urban context. Two new tools (urban pollutant load modelling and evaporative cooling) were added to LUCI based on previous studies. Blue-green infrastructure (BGI) benefits of five urban ecosystem services were evaluated: (1) flood mitigation, (2) carbon sequestration, (3) water purification, (4) habitat connectivity, and (5) evaporative cooling effect. The fundamental spatial input data for analysis are a digital elevation model (DEM), land cover information, and soil information. A fine resolution DEM at 1 m reflected local spatial and functional details. The kererū/NZ wood pigeon (Hemiphaga novaeseelandiae), pūtakitaki/paradise shelduck (Tadorna variegata), and the generic NZ gecko (Haplodactylis) were selected for the habitat/patch connectivity analysis. Verified parameters from the Modelled Estimates of Discharges for Urban Stormwater Assessments (MEDUSA) were used for urban pollutant modelling. The evaporative cooling effect was estimated using field observations, expert knowledge and literature values on local shade, evapotranspiration, and albedo of green infrastructure.

LUCI simulation results yielded information regarding the degree to which ecosystem services were supplied for the different scenarios that were investigated. The main flood mitigation areas Hagley Park and Travis Wetland were identified for the Ōtākaro/Avon River catchment. High flood concentration areas were the Ōtākaro/Avon River Corridor, the Cranford Basin and the Addington Brook sub-catchment. Hagley Park and Travis Wetland were also found to provide high carbon sequestration rates. Habitat connectivity would be improved by implementation of BGI, with habitats of interest for kererū and pūtakitaki increasing from 0.6 % to 3.3 % and from 1.2 % to 2.5 %, respectively. The habitats of interest are increased by expanding some existing habitats for kererū breeding and nearby foraging, for example, Hagley Park and other Council owned land. Pollutant loads (total suspended solid (TSS), zinc (Zn), and copper (Cu)) were quantified and a reduction (2 - 12 %) of TSS, Zn and Cu for the whole catchment can be achieved with the proposed BGI systems. Pollutant loads were also analysed under future climate change and the results reflected the uncertainty in climate change predictions. The potential for temperature reduction through green infrastructure and adjusted land use types in the Ōtākaro/Avon River catchment was demonstrated. The boundary of Hagley Park and the boundary around Horseshoe Lake where trees were planted in the past were identified as areas with high temperature reduction potential (2.8 to 3.5oC). The trade-off analysis revealed that Travis Wetland in particular was able to provide multiple benefits, i.e. flood mitigation, carbon sequestration, habitat connectivity, and cooling.

A DEM, soil classification, population density (people/ha), and planning rules for each land use were used as input data for UrbanBEATS stormwater tanks modelling at 500 x 500 m spatial resolution. Lot (property parcel) and neighbourhood scales were selected to determine the necessary sizes, density and capacity of stormwater tanks that would achieve a target 30% potable water substitution and 70% volumetric supply reliability. The optimum configuration of stormwater tanks considered different climate change scenarios as well. The results showed that stormwater tanks are a suitable adaptation measure to urban stormwater management under climate change for Christchurch, supplying water provisioning and flood mitigation services. Firstly, stormwater tanks saved up to 30 % of potable water demand, with 70 % tank reliability, when specific proposed locations, density and size of stormwater tanks are met (2 m3 for the smaller scale and 5.3 - 6,576 m³ for the large scale). Secondly, most of the large-scale stormwater tanks were big enough to attenuate floods (> 9 m³ - the recommended size from Christchurch City Council for flood attenuation).

Overall, this research contributes to improving the understanding of ecological benefits provided from selected blue-green and grey infrastructure of an urban environment at catchment scale using the refined LUCI and UrbanBEATS modelling tools. Specifically, it has been identified how land use change and implementation of blue-green and grey infrastructure alters urban ecosystem services, both under current and future climate change conditions.. Such information will prove useful in urban planning and policy, as well as design of sustainable and resilient cities.

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