I think the only Winter Series event that has been seriously flood-affected in the past has been my Stansted Airport Express, with several rivers on the route that are prone to overflow, a couple of fords, as well as that notorious dip under the old railway bridge at Takeley Street (hello Big Saxon!).
Huggy may have some organiser's wisdom to impart. Just reading through the route sheet I can't see any potential issues for Saturday's ride, apart from the Chelmer at the foot of North Hill, at Papermill Lock. If the river is very high a section of the road does get flooded (there's a depth gauge alongside the road after the bridge). From there it's only 10km to the finish, so wet feet might be more bearable! If it's as wet as forecast, there will certainly be some big puddles - I'll be going top-to-toe waterproof coverage including long waterproof socks!