These trenches act as trap for the water and minimise soil erosion. The trenches do not need to be very large to be effective. A trench about 10 feet long, one foot wide and one foot deep is very effective. Try to stagger them on the hillside so that water is slowed evenly across the entire slope. This technique should only be used where the trenches will not complicate the use of the field. However, if the field is being used for grazing of animals, they could be injured in holes and trenches.