How increased urbanisation has induced flooding problems in the UK: A lesson for African cities?

摘要

This paper explores the relationship between increased urbanisation and subsequent capacity problems within drainage infrastructure. The respective merits of resolving these problems using: (i) 'quick fix' engineered solutions and (ii) long-term 'planning-based' remedial measures are investigated for a UK case study catchment. In the UK context a 'quick fix' approach would often involve the provision of in-sewer storage (e.g. a storage chamber or oversized sewer pipes) to store excess flows, releasing them back into the sewer later for subsequent conveyance to a treatment facility or outfall. SuDS retrofitting may represent an attractive alternative to this 'hard engineering' approach, but has proved difficult to implement under the UK's current regulatory framework. A long-term 'urban planning-based' approach, on the other hand, involving the imposition of 'pre-urbanised' (greenfield), or even stricter, runoff restrictions to all new developments (or redevelopments) within urban areas could incrementally reduce the storm-water runoff entering the system over time. Historical maps are used to demonstrate how the case study catchment has become increasingly urbanised over the last 50 years; and a simple modelling exercise demonstrates how this process has been directly responsible for exacerbating the catchment's flooding problems. The case study also demonstrates practical opportunities for reducing or resolving the flooding problems with 'quick fix' engineered solutions, retrofit options, and long-term 'planning-based' remedial measures. These issues are specifically illustrated for a UK case study containing known 'surface water' flooding problems, but parallels to the urban African context are drawn and discussed.