Work to improve flood defences in Lewes should be underway within a year.
The Government has given its approval to plans to reinforce walls surrounding Malling Brook.
The move has given the Environment Agency the green light to proceed with investigations in the area, in the hope of gaining final government approval within months.
The work will mark the first phase of the Ouse Flood Defence Strategy, which is expected to cost a total of £10 million.
Malling Brook improvements are estimated to cost about £1 million.
The Government has also given its stamp of approval to investigations into creating a tidal flood storage area on a flood plain downstream of Lewes.
Agency officials are also considering how to make use of overflow channels in Uckfield and Lewes by constructing scale models.
The agency's Sussex area manager Peter Midgley said: "The details of the final plan are complicated and it is essential they are correct so that the scheme not only works well but also uses the public purse wisely.
"Nobody will be happier than myself and my colleagues at the Department for the Environment, Food and Rural Affairs when the appropriate flood defences are in place.
"We hope to be able to do this in Malling Brook by the end of the next financial year."
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