Applications of Best Practice Water Sensitive Urban Design Solutions on the Ebbsfleet Development
This thesis sought to address the growing vulnerability or urban environments to stormwater runoff and flooding through the increased impervious surface area, commonly from roofing, paving and roads. This can cause significant peak flows of stormwater that have the capability to overload the local drainage system capacity. Water sensitive urban design has emerged as an approach to return urban environments to a more conventional natural water drainage cycle by utilising blue-green drainage infrastructure.
The Ebbsfleet Development was chosen as a relevant case study given the ongoing work with the Urban Flood Resilience research group and the significant uncertainties in drainage demands from the effects of urbanisation and climate change. By assessing the current and future applications of water sensitive urban design through a comprehensive literature review, a range of measures were found from international best management practice examples, broadly split into asset and process applications.
An adaptive planning framework was utilised with real options analysis to value managerial flexibility in the face of inherent, deep uncertainties when designing the drainage infrastructure. Comparison of the option pathways was modified from the conventional discounted cash flow analysis to incorporate analytical hierarchy process using a range of criteria that can be altered through stakeholder engagement to reflect local priorities.
The rational method was used to calculate the drainage requirements for three scenarios over a 50-year design period to reflect lower, greater, or expected discharge demands from the catchment area. This first approximation used data available in combination with assumptions to assess four option pathway approaches. It was shown that an adaptive mix approach, utilising a hybrid combination of blue-green and grey infrastructure provided the greatest return on investments accounting for externalities.
However, this information must be framed to highlight the benefits to urban developers, responsible for delivering the final on-the-ground drainage solutions. There is scope for further work to apply and scale this tool on with real-world decisionmakers to refine the process for future applications, within the UK and further afield.