Chichester emergency flood alleviation project, winter 2000/2001

Abstract

The River Lavant is a small ephemeral chalk stream, which is culverted through the city of Chichester. In 1994 widespread flooding resulted when the capacity of the culverts was exceeded and the river overtopped its bank. Subsequently a local multi-agency Strategic Coordinating Group was formed, and a permanent flood alleviation scheme was developed through the planning process. In November 2000, after a period of very heavy rain, the River Lavant again threatened flooding. A large-scale pumping operation to divert some water around the city was brought into place by the Fire Brigade. Additional alleviation capacity was urgently needed, and local design resources were committed to adapt the permanent scheme for rapid implementation. The project comprised several major pumping operations and open channels over 5 km long with a choked diversion to protect the village of Merston. The A27 trunk road and the railway embankment carrying the mainline along the south coast lie across the route. Piped crossings were designed involving liaison with Railtrack and the Highways Agency. Documents for the whole scheme were put together while funding approval was sought. Despite the emergency conditions, both archaeological and ecological studies were undertaken, particularly for water vole, bat and badger habitats. On 4 December 2000 construction commenced in three packages costing a total of £1·3 million, with a programme to complete all but the main rail crossing before Christmas. However, further bad weather intervened, and the partially completed works were brought into use carrying floodwater less than two weeks later. In the New Year the rail crossing was constructed during a weekend possession. The paper focuses on the implementation of the project, including emergency response, multi-agency cooperation, team working, fast-tracking approvals, unique technical solutions, and rapid construction while ensuring compatibility with the full scheme.