There's a creek bed running through my property that's as apt to have standing water throughout the year as it is to be dry. With the rain we've had lately the creek has jumped its bank at the lower end and flooded what I call the "delta". This, unfortunately, is not an unusual occurrence. It's a big area of soil adjacent to gardens so leaving it unplanted isn't an option.
Before going on let's underline there's a big difference between wet and periodically flooded. There are many plants that will perform and please in wet soils (defined as often saturated, but rarely with standing surface water). Floodplain sites, on the other hand, will have standing surface water for one or more days at time, multiple times per year.
I'm always entertained by customers, who upon questioning, smilingly say: "Well, water does stand in that area for more than a day at a time- but it's only a handful of times a year." That's like saying you can only drown in the bathtub if there's water in it :) It's as important for roots to get oxygen as it is for our lungs. So, always go for the worst common denominator and realize that if you have these delta-like sites you need to use flood-tolerant plants, such as:
|Swamp White Oak|
|Baldcypress leaves, tree pictured at top|
|Arctic Blue Willow|
|Red Sprite Winterberry|
|The Rocket Ligularia|
|Sweet Caroline Hardy Hibiscus|
Over the years I've tried and lost a lot of plants in the delta. The above have all survived flood "tides" with flying colors.