It is well known by engineers and town-planners that the run-off co-efficient of an urban area is high (0.95....) while that of a natural forest is very low (0.05). THis shows that very little of the water that falls on the forested area actually runs off rapidly. Most of the water is collected and stored in the surface leaf litter and the top soil layers. These areas are high in organic material, which has the ability to hold large volumes of water.


So, replanting all areas that are not directly needed for production is a valuable and effective water harvesting strategy - on a reasonably large scale.