If this is the only ephemeral pond for miles, I might agree with you, Tyler. But honestly, if a water feature slowed the progress of water off of my property, I would make one into a pond.
Mind you, I would take all the measurements possible of the area before I started, and I would probably ensure there were adjacent areas left to do their ephemeral thing, or I would see what other structures could possibly encourage the type of ephemeral ecology necessary. But unless we're talking about endangered or at-risk species, I think many responsible permies could do better for diversity and carrying capacity of the land than the conservation of what, in many necks of the woods, are mosquito breeding pits.
I think that if there were any areas of observable outflow from the potential or ephemeral estuary in question, one might place a square bale straw dam across it, depending on how strong the inflow is. Just keeping the water there longer may cause natural formation of a biological gley layer, which will keep the water there longer as well. Trapping sediment and nutrients, both from the stream and from off the land, are some beneficial side-effects.
I would be careful to ensure that water has ways to pass relatively unencumbered even at really low levels from the stream, and I would plant into or around the bale dam with reed bed species, and probably work riparian trees into the mix where the ground could support them. Depending on where you are, willow would be great, and if they live where you are, cottonwood tend to pump water into the air when the humidity drops. Increases in
shelter and ambient humidity controls will moderate extremes and stretch out any conditions that foster ephemeral ecology.
I was trying to work straw bale chinampas into the plan somehow, but except for planting up straw bale sedimentation and water slowing dams in riparian species and maybe some human or wildlife food, I am at a loss.
-CK
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein