Here is a roadside hedge that captures water and silt/gravel movement from a bitumen road with dirt driveways nearby. So far, approximately 10-15cm of material has been caught behind the hedge. This hedge is shaded from Autumn onwards in the North and somewhat shaded in Summer from the South, thereby not being as thick and robust as it could be.
Even being thin, and with an obvious hole visible in the hedge, any fixed obstruction to water movement is a benefit. This one has the benefit of creating mulch for the planting behind it.
