Which outcome arises when a major river's stream gradient decreases due to regional tectonic subsidence?

💡 Explanation

When tectonic subsidence decreases a major river's stream gradient, the flow competence is reduced because the river's energy declines, leading to increased sediment deposition and floodplain construction. Therefore, aggradation and floodplain widening results, rather than incision, increased velocity, or reduced delta sediment, which depend on increased stream power.

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