I have planted a new orchard in a field with erosion problems. The soil is vulnerable to water erosion due to a combination of slope and clay in the subsoil. Heavy rains had created rills and soil was carried away year after year. The good news is that this problem is confined to two low points where tributary rills convey, so I have been able to tackle it.
When water can not be drained away quickly enough, a temporary runoff does the job . That happens from top to down in the slope. However, rills are created from down to top, carving the soil in an upward movement. That happens because little tributaries merge to form a greater water course. Water speed carries fine particles in these sites, braking the surface and increasing the water gradient and speed, so erosion is magnified in a cascade effect.
This process can be prevented if the water exit is modified with coarse material. A mass of peebles and small stones is difficult to erode. If you locate it down where erosion starts, you can halt it in an effective way. I have done so in the field. I located those peebles in the lower parts of the rills, and repeated it every 10 meters uphill. I did so close to the most afected tree sites and also added some organic substrate to the trees in order to compensate the soil for the years that was affected by the runoff. After that, normal cultivation levels the field and the soil has a discreet protection when the next storm strikes.