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| I will speak to what I know. I will put in a disclaimer that I probably know enough about this "to be dangerous". If I mis-speak, or state something wrong, someone who knows more than I know can correct me.
My understanding is there are 3 types of water erosion: sheet erosion; rill erosion; and gully erosion. Gully erosion is what you referred to - where you have low areas in a field, the water concentrates in those areas, and forms gulleys. You install sod waterways to control this.
Sheet erosion is where the soil/field has the ability for soil to move downslope in a field - uniformly. You really cannot see this happen - unless it is really severe.
Rill erosion is where you have a series of rills - "miniature gulleys" - that form across the slope of the field. In contrast to gulleys which form in concentrated areas, rills form across broad areas of the field.
RUSLE & RUSLE II does NOT measure/calculate/estimate gulley erosion. This is identified by visual observation - which you appear to be competent in doing. RUSLE & RUSLE II estimate sheet & rill erosion - erosion which occurs across broad slopes of the field. The longer the slope, the steeper the slope, the more time the soil is bare, the greater the opportunity for this type of erosion to occur.
The way to control sheet & rill erosion is to: 1) keep your soil covered (cover crops, no-till planting, high levels of crop residue, etc.); 2) reduce the length of slope of your field . You can do this by breaking the field into strips of alternating crops - every time water runs downs the slope and it encounters a strip change, it slows down the flow of water; 3) installing terraces. Most farmers do not like terraces. In fact, having the soil covered - crop residues & cover crops - is more effective than terraces. That is why you see a push to no-till and less of a push to install terraces.
I hope that answers a few questions. If you have more, please ask.
Martin
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Explain "soil erosion" to me................
