What are the circumstances in which swamps or everglades can have dramatic low and high tides?

Question

I'm actually trying to create an alien ecosystem, so changing orbits, what's exhibiting tidal forces and the geography and such is welcome if needed. I also wonder how stable a setup with dramatic tides (flowing into an otherwise stagnant area) would be. The point of this specific ecosystem on my planet is the evolution of the dominant race; they evolved in fertile swamps that had dramatic tides. The high tide would be about 7 or 6 feet deep or so (essentially tall enough for a human to swim in), and the low tide would be knee/ankle deep, with days where there's almost no water at all. Anyway, it would need to be stable enough for a species to evolve and adapt to it.

BONUS: It would be helpful to know how this setup could develop, too, but that information is not necessary. I really only need to know if it is possible and stable.

Answer 1

Mangroves in an area with naturally high tides works

Here is a mangrove forest in Kiribati at high tide:

Here is one in Thailand at low tide:

Mangroves are designed for this sort of enviornment. They are able to grow in salt water by diffusing all the salt that they suck in from their roots into sacrificial leaves, which are then shed.

The next thing you need is to find a place that has high tides. Fortunately, I happen to know of a place that has mangrove swamps and also huge tides. Bissau, the capital of Guinea-Bissau in West Africa has around 4-5.5 meter tides, or 14-18 feet. At 6:54 am this upcoming morning (in Africa time), the tide is predicted to be 0.17m, or 0.6 feet. By 12:28 pm, or 6 hours later, the tide will be 5.41m or 17.7 ft.

As for fertility, there are lots of fish to be found in these places, so if your people are fish-eaters or maybe Sahuagin, they should do well here. Agriculture is a tougher call, in salt water, but they could also grow bugs fed on tree leaves, farm shrimp in pens or a variety of other things. Incidentally, Bissau also has a powerful monsoon, so the tide marshes fill with fresh water and dirt washed down from the hills once a year, which is good for re-fertilizing the soil. I'm sure you could come up with some adequate food chain for an intelligent species.

This should be the sort of environment and tidal variation you are looking for. So, it is possible and stable, because it exists on Earth.