Thick, healthy vegetation contributes greatly to slope stability by holding the soil together with it's root structure. Carefully examine the quality of the vegetation on the slope. Planting the right combination of riprap protection, gabions and vegetation. Leaves and pine needles on the soil surface can also help prevent erosion. This is common when a coarse layer of sand overlays a less permeable soil such as clay.
Water tends to move rapidly and freely in the sand.
Once it reaches the less permeable clay layer, it tends to flow along the clay surface and exits the slope face. Consulting a professional engineer may be a good idea. Providing footpaths with clearly defined borders and an acceptable, clearly marked parking area away from eroding slopes will help relieve this problem. Limiting access to eroding areas and slopes by installing barriers and planting prickly vegetation will also help. Vehicles parking close to the water's edge can cause compaction, and can tear up existing vegetation.