Resilience of Water Sensitive Design Assets in Urban Environments Against Flooding and Climate Change

Urban sprawl has led to the conversion of previously natural, pervious land into impervious surfaces. Consequently, this increase in impervious areas has elevated the risk of urban flooding. Water Sensitive Design (WSD) assets are engineered green infrastructure implemented in new urban environments or retrofitted into existing ones. WSD assets, inter alia, have been largely successful in controlling flows from urban catchments and providing pre-development hydrology whilst mitigating the risk of flooding. Abundant research exists around quantifying the performance of WSD assets for their flood mitigation in terms of peak flow/volume reduction. However, it has been identified through the literature review carried out in this thesis that current flood resilience metrics focus on quantifying the performance of these based on flood volume/duration. WSD assets are identified to not only reduce catchment flooding but also control other parameters within a catchment. Hence, a measure of how resilient these WSD assets are based on a more holistic metric is deemed a fairer method of assessing performance compared to currently used indicators to measure flood resilience. This research developed a novel flood resilience metric through a literature review and research to quantify the resilience of WSD assets against flooding in urban environments. This normalised resilience metric compares the resilience of a catchment (with modifications to improve resilience) with the existing state of the catchment, allowing a score between 1 and 0, with 1 being the best level of resilience achievable for the catchment, and 0 being no improvement in resilience. The results show that WSD assets are the best method of mitigating urban flooding for the current climate for small and large flood events (with an average resilience of 0.66, and 0.32 respectively), across multiple rainfall events. The conceived flood resilience metric was able to identify that methods that were previously thought to enhance flood resilience (e.g. improving stormwater conveyance by increasing conduit capacity in a catchment), were in fact, reducing the catchment resilience, as even though they provided a reasonable level of resilience against catchment flooding, they had a low resilience for outflow volumes and outflow rates from the catchment. Following this, with the use of climatically adjusted rainfall data, predictions were made on the level of resilience that these WSD devices could provide in urban environments for future climates. The results ascertain the variation in resilience with a changing climate, and the developed resilience metric was able to identify improvements that can be made to the WSD and the catchment itself to enhance urban flood resilience into the future. Thus, this resilience metric would be a critical tool be used by decision makers to identify how to best to implement WSD assets into urban environments to best supplement the urban drainage infrastructure to mitigate urban flooding in the current climate, and into the future.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Civil Engineering

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2025

Author dc:creator

• Dharmasena, Thivanka Vishwajith

Advisors dc:contributor.advisor

• Zorn, Conrad
• Shamseldin, Asaad

• Urban Flooding
• Stormwater Modelling
• PCSWMM
• Flood Resilience
• Climate Change

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/75320

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/75320