Hey Rick...
When I think of rain water collection, I'm thinking that in most instances it's from the roof via gutter into barrels for later use. However, other uses of rainwater are through diversion on the ground by way of trenches to the base of trees and into beds, swales which are small dams that both collect rainwater into organic material such as dead wood and mulch, as well as divert it into a holding area like a pond, pool, or reservoir.