As Brian Richter says, the ...

As Brian Richter says, the best way to get result is through satellite imagery measurements. Apart from that erosion pins, it depends on type soil present near river banks, infrastructural activities that may involve in erosion of the bank and natural erosion of soil either through precipitation or through sudden surge in river flow released by nearby dams or reservoirs. For one of my academic projects, I needed to estimate erodibility factor on land surface due to precipitation, I used RUSLE factor, as I had few hands on data.