Pelham Brook joins the Deerfield River in Charlemont MA, about 5 miles downstream from Fife Brook dam. Where a smaller tributary enters are larger river, it is not uncommon to see large rocks pushed out into the main stream from the smaller one. This is particularly true on a regulated river like the Deerfield; upstream dams will modulate high flows during floods, while the unregulated tributary may experience very high flows, and thus have the ability to move large materials. These are deposited well into the main stream, and flows are forced towards the opposite bank. Notice the eroded bank on the far shore, particularly visible in the June 4 image.
This phenomenon of tributaries altering the flow of the receiving river, with consequent bank erosion on the opposite bank, occurs in at least two other nearby locations; at the confluence of the Cold River and the Deerfield, about a mile downstream of this image (https://riversmartvt.umass.edu/virtual-tour-stops/533/543); and at the Black Brook / Cold River confluence, about 2 ½ miles up the cold river. In the latter case, both Black Brook and Cold River are unregulated by upstream dams. However, in this case a general principal may apply; the smaller stream will typically have a steeper slope than the larger stream, and thus may be more capable of carrying larger materials in high flows. This may explain the presence of large rocks and boulders cutting across the flow of he larger stream, and directing the flow towards the opposite bank. During Irene, the bank eroded right where a bridge abutment stood, rendering the bridge impassible until repairs could be made. LINK HERE.