posted 11 years ago
Without knowing the volume of water involved, it is impossible to come up with advice that would fit your circumstances. If you are in an arid or semi arid region that gets rainfall in small doses, your design would be much different (and easier) than if you live in a tropical region that gets sudden, heavy downpours, where any dam would need to be designed by a pro that understands fluid dynamics, and conservation issues.
For a low flow system, one easy and inexpensive way to collect the run-off top soil is to partially fill the hollow with cut brush. This slows the flow of water so that the topsoil has a chance to let gravity sink it to the bottom rather than spewing across the road and away.
However, if you live in an area that occasionally gets 4" in a single day, you may not want to do anything that could result in disaster.