A 25m-wide overflow channel -- rivalling the size of the River Thames -- is one of two schemes being considered to prevent flooding in Oxford.

The £100m channel, which would skirt the west of the city from Binsey to Kennington, was one of more than 50 potential schemes to combat flooding.

Engineers at the Environment Agency has confirmed that a giant flood relief channel remains very much in the running along with a rival scheme to widen existing streams in the Thames's floodplain.

But problems remain with plans to widen existing streams because many, such as Bullstake Stream which runs under Botley Road, are closely bordered by housing developments.

The EA has not ruled out working the two schemes together but the idea of a 25 metre-wide channel sparked concerns from environmentalists.

With the Oxford floodplain containing a number of protected sites of Special Scientific Interest, the Wolvercote botanist Dr Alison McDonald and the MEP Caroline Lucas were among those to raise concerns about the impact on Port Meadow, Wolvercote Common and other sites protected at European level.

The EA says it is also to examine change of land use upstream of Oxford, with extensive tree planting on pasture land seen as a way of slowing the passage of water. It will also consider storing flood water in reservoirs upstream of Oxford, for release back into the Thames and River Cherwell when flows return to normal levels.

The spokesman said: "The results of the testing highlighted over 50 potential solutions to the problem of flooding in Oxford.

"Each was then assessed to establish how well it would perform in the rigorous feasibility tests set by Government to ensure that any scheme is cost-effective, technically-achievable, and is not damaging to the environment.

"Only schemes that succeed in all three areas will be considered for funding. From this work a final short-list of options was drawn up. These are all based on the two core solutions."

The idea of a giant underground flood water store has been ruled out as impractical from an engineering perspective because of the huge amount of water involved.

The widening of the Thames to increase its flow capacity was also rejected, because of the environmental impact and cost of widening and replacing bridges and property next to the river.

The EA says the intention is to reduce the risk of flooding to about 3,500 properties located in the Oxford floodplain.

The agency plans to seek Government approval by 2007, with construction unlikely to begin