Sadman Islam

Increasing populations and migration towards built areas are driving the growth in urbanization, resulting in increased stormwater runoff into receiving water bodies, increased flood peaks and degraded runoff quality. Initial challenges of conveying stormwater runoff focused solely on easing flooding through a network of grey infrastructure including conveyance pipes and detention facilities. New methods for stormwater management involve the use of Sustainable Urban Drainage Systems (SuDS) which serve not only flood attenuation and water quality improvement functions, but also deliver a range of socio-cultural and environmental ecosystem services, such as air pollution mitigation, habitat enhancement, improved health and well-being etc. However, current literature mostly evaluate SuDS based on a single functionality or ecosystem service (ESS) and fails to describe the linking interactions and interdependencies between them.

This dissertation focuses on the two main functions (surface runoff management and water quality improvement) and a set of five ESS (noise mitigation, carbon sequestration, air pollution mitigation, biodiversity enhancement and amenity value uplift) that can be derived from SuDS using green infrastructure (GI). The research highlights key parameters for quantifying each function and ESS. It then seeks to assess the magnitude and interactions between the benefits obtained from such an installation, by establishing a hierarchy of desired benefits amongst a stakeholder group and changing the design parameters and environmental conditions.

The research methodology consisted of an extensive literature review to identify ways of evaluating the primary functions and additional ESS of SuDS. This information was then applied to a particular type of SuDS called bioretention cells in Brunton Park, which were put in as a flood management mechanism in the Ouseburn catchment in Newcastle. A range of different positions were then considered from the point of view of Brunton Park residents to develop a list of prioritised benefits, through an Analytical Heirarchy Process (AHP) which is a form of multi-criteria decision analysis (MCDA). This was then used to change certain physical parameters of the bioretention cells to satisfy residents, which then highlighted the gains and tradeoffs between the functions and ESS. Soil moisture, vegetation coverage along with planting substrate type and source were identified as key parameters that govern the operation of the core functions and additional ESS. While increasing soil moisture and vegetation coverage reduces the water storage capacity of SuDS, changing to a higher infiltration rate planting substrate can improve runoff management but has a detrimental on water quality improvement. Increased soil moisture also causes noise absorption to drop rapidly which can be countered by increasing the vegetation cover. It was also found that, a larger leaf surface area promotes carbon sequestration, air pollutant absorption, biodiversity and amenity value. However, carbon sequestration only occurs in discrete periods (during plant growth) whereas the remaining four ESS occur continuously. Planting substrate that is not native to the region where the SuDS is installed creates a large carbon footprint due to transportation and reduces the ability of the SuDS to adapt to climate change. Finally, obtaining benefits from a SuDS depends largely on its maintenance regime, where debris removal, weeding and watering (during dry periods) need to be done properly to ensure the survival of the vegetation cover and to prevent harmful pollutants from being released during the first flush.
This study shows that SuDS do not simply deliver their primary functions, but are versatile structures, producing multiple services which can be exaggerated or diminished by changing certain parameters.