A naturalized basin is a detention basin designed to behave like a wet meadow instead of a bowl of mown turf. It performs the same hydraulic function and does several other things at the same time.
Deep-rooted native vegetation and an amended soil profile increase infiltration across the basin floor. A share of the runoff soaks in rather than leaving through the outlet, which reduces both peak discharge and total volume downstream.
Dense vegetation slows sheet flow, and slow water drops sediment. Plant roots and soil biology take up nutrients that would otherwise reach a creek. Water quality treatment becomes a property of the basin rather than a separate structure.
Established native root systems hold banks and the basin floor through repeated wetting and drying far better than shallow-rooted turf, which is why naturalized basins usually need less repair after large storms.
Mowing twice a year rather than twenty times is a meaningful line item over the life of a development. The trade is a establishment period of two to three growing seasons, during which the planting needs real attention.
A fenced concrete pond is a liability on a site plan. A planted basin with a walking path around it is open space, and it supports pollinators and birds while it does its engineering job.
The hydraulics are identical. The difference is what the site gets for the same acreage.