Simply to try something different and see what happens. I was thinking that some red mangroves would look awsome along with some schooling fish. The portion that has water 365 days a year would have regular aquatic plants. The other portion would have mangroves. Durring the "wet season" I'm sure many of the aquatic plants would grow up onto the higher terrain, and as long as the transition was fairly slow, some may even survive being out of the water (I know that my sword plants almost always were growing right up out of the aquarium). It would be interesting to watch fish swimming in an area that was previously land only a few weeks ago, and then return to the lower portion during the "dry season".
Living in arizona, it is interesting to see how some washes become rivers during the monsoon, and then become dry beds during the winter. I could try something like this, however desert plants do not enjoy being up to their leaves in water for more than a rainy day or two.