Sentinel 1 (S1) is a radar ...

Sentinel 1 (S1) is a radar sensor of 10 m resolution, each five days you will have an image ( depends on the location).

The nice feature of S1 is that it provides data regardless of water turbidity and cloud cover.

If 10 m is not  enough , then you have to use high resolution sensors of 0.5 meter, but these are optical, i.e. affected by cloud. 

Sensing technique will also define the method to delineat river banks (river shoreline).

For optical sensors use the the water index, simple band ratio. Or if the sensor has a NIR band, u can use a simple threshold to delineat river banks. For radar, a simpl thresholding would work also (care with polarization).

For erosion deposition, for optical & radar, apply first delineation (of river banks)  and then use a standard change detection technique.

Cheers

Suhyb