I have seen that infiltration basins can be a valuable tool in order to get water in the ground, and to the surrounding plants.
Here is one on permies.
and Mark Shepard and Geoff Lawton talk about how Infiltration Basins are used on Mark's landhere.
But I am wondering if there is any knowledge out here about: how wide of an area an infiltration basin would be able to provide for the needs of a water loving plant? I would assume that it depends on the slope that the basin is on, causing the water to flow underground in a specific direction.
Daniel, maybe you should look into diversion swales to help supplement your water loving plants. This will help catch more water from a larger area and dump it into your infiltration basin. I think you should also look into making your IB deeper than normal, since more water will be coming in.
Of course, this all depend on how much rain you get, your climate, etc. The less water you get, you would make your IBs broader, especially if you want water loving plants in them.
Not sure if that helps or not, but that is the knowledge I have/can provide in regards to what you are asking.
Brad Lancaster talks about dimensions in his Rainwater Harvesting book one or two. I would highly recommend both as reference guides for numbers. I think he says the width should be the canopy of the tree and the depth should be about nine inches, four of that being filled with mulch.