Many people in Banbury recall the Easter of 1998 not as a time of celebration but as a time of severe devastation. Heavy rain caused a flood which closed the railway station and many roads. Approximately 125 residential and 35 commercial properties were affected, resulting in more than £12.5 million of damage. Another flood in the summer of 2007 reinforced the need to fully implement a flood alleviation scheme.
The geography of the valley along the river that runs through Banbury made the community particularly susceptible to flooding during heavy rains. The Environment Agency, a public body crucial for delivering the environmental priorities of the central government – including managing flood risk – engaged Black & Veatch to provide the study and design services for the Banbury Flood Alleviation Scheme.
The flood alleviation scheme consists of five major elements: 1) a large flood storage reservoir upstream of Banbury, 2) a key highway with raised elevation into the community, 3) new earth embankments, flood walls and pile walls in strategic locations, 4) a new pumping station and 5) a bio-habitat, complete with ponds, trees and hedgerows.
The team worked together to identify ways to reduce costs for the client and overcome challenges. Availability of material was a significant challenge. A local borrow pit provided 100,000 cubic meters of earth needed for the reservoir embankment. Limestone blocks discovered in the borrow pit were used as an alternative to stone-filled gabion baskets in the river, or crushed to provide granular material for the haul roads. This removed the need to import material.
The unique manner in which floodwater is managed sets Banbury Flood Alleviation Scheme apart. The rate at which floodwater is impounded in a new storage reservoir is controlled entirely by the shape of special structures. Commonly, such control is achieved though a system of gates that require power, control systems, and often an onsite operator. At Banbury, these are unnecessary.