The study looked at how water runoff and erosion affect coal mines. They tested different water flow rates to see how erosion changed. They found that slow water flow caused small rills, while fast flow created big gullies. The speed of water on the flat part was slower than on the slope. The amount of sediment washed away was much higher on the slope than on the flat part. Gullies were wider and shallower on the flat part, while on the slope they were narrower and deeper. This information can help predict erosion in coal mines.