Soil erosion transports soil from someplace you wanted it to stay, to someplace you did not want it to go.  Although soil erosion is a natural process, the actions of people have been known to greatly accelerate it.  Unfortunately, those who accelerate erosion don’t usually volunteer to transport the soil back to where it was.

How Do People Accelerate Soil Erosion?

Human activities frequently divert water from where it was going, to someplace it did not go before. Think about how drainage patterns were revised, and how to prove it. Perhaps there are some previous photographs, or a previous topographic map or survey. More water creates higher flowing velocities which transports more soil. We have also seen cases where piles of loose soil were dumped into an existing ditch or flowline, then they were washed away later.
The steepness of the slope can be increased by placing fill materials on the uphill side or excavating on the downhill side. Either of these scenarios will usually increase the tendency of soil to erode. Did either of these happen? Can you prove it with photos or other documentation?
The tendency to erode varies greatly between various types of soils. Gravel and big rocks are more resistant to erosion because they require higher velocities to keep them moving. Silt particles are easily mobilized and will also remain suspended at relatively low velocities. Whether or not a particular type of soil is likely to be eroded can be determined by industry-standard calculations, or charts and tables in-lieu of calculations.
Since erosion is a huge problem, many solutions are available. Entire manuals have been written about erosion control measures. Hundreds of techniques and products are routinely-implemented in accordance with industry standards. Erosion can be reduced to virtually nothing by implementing industry standards. Those who caused erosion should have paid to reduce it.

Try This:

Perhaps you can find pre-erosion photographs, such as aerial photographs of the pre-existing (non-eroded) condition by searching online (try using Google Earth or Maps).

Resources for Further Research

Whatever jurisdiction you live in, there is probably an adopted drainage and erosion control manual. Search online to see if you can download it.  If you see soil erosion, it is likely to be the result of not following the guidelines for your jurisdiction.