What can trigger head cut migration?

Head cut migration is a geomorphological process where a channel's upstream area experiences erosion due to a change in elevation, which leads to a downward cutting into the bank or bed. The degradation of the channel is crucial in this context because it often results from factors such as changes in flow velocity, sediment transport capacity, or base level changes caused by erosion or human activity.

When the channel experiences a reduction in elevation downstream, it creates a situation where the upstream channel becomes unstable, thereby facilitating the process of head cut migration. This erosion tends to move upstream over time, as the head cut propagates backwards into the channel landscape. Therefore, the correct answer identifies a fundamental mechanism behind this phenomenon, highlighting the role of channel degradation in initiating and sustaining head cut migration.

In contrast, increased sediment accumulation generally promotes stability in channels rather than erosion. Natural vegetation can serve to stabilize banks and retard erosion, while barriers across the stream can disrupt natural flow patterns, potentially halting head cut migration rather than triggering it.