I'd go for an August plot. One thing that does well in flooding is Alsike clover. It's really cheap and only lasts a few years but who cares- just keep re-seeding it. If it floods so bad that it dies, not a big deal BUT it stands up really well to flooding. You can read more on it on places like Welter Seed's website.
If it were me, I'd try some clover now after you kill off area really good- alsike with maybe some white clover of some type too. OR, I'd wait til August and plant a combo of winter rye, winter peas and throw in the Alsike clover.
Alsike is a unique one that may stand some flooding for a bit BUT the August suggestion of rye and peas obviously will be fine.