Based on specific observations in the lower sections of a stream, discharge (the volume of water flowing in a stream channel per unit of time) plays a role in the rate of erosion, particularly through its interaction with the stream's gradient (slope).
Discharge, Gradient, and Erosion in Stream Channels
In the lower reaches of a stream, the volume of water (discharge) is typically much higher than in the upper sections. This higher discharge, combined with often lower friction along the streambed compared to steeper, rockier upstream areas, significantly impacts the stream's ability to transport sediment.
The Role of High Discharge in Lower Reaches
With greater discharge and reduced friction, the stream possesses considerable energy. This means the stream does not require a steep gradient to effectively move its sediment load downstream.
When Erosion Occurs: The Gradient Adjustment
The provided reference highlights a specific scenario:
- Context: Lower stream reaches with high discharge.
- Energy for Transport: High discharge and low friction mean the stream needs only a gentle slope to carry its sediment.
- Potential Mismatch: If the stream's actual gradient is steeper than what is necessary just to transport the sediment load, the stream has excess energy.
- Erosion as an Adjustment: This excess energy can lead to the erosion of the streambed and banks.
However, this erosion process itself has a direct consequence that affects the rate of further erosion. By wearing away material from the streambed, the stream effectively reduces its own gradient in that location.
As the reference states: "...this would decrease the gradient leading to a decrease in erosion."
The Feedback Mechanism
Therefore, according to this specific mechanism observed in lower stream reaches with high discharge, the effect of erosion is a form of self-regulation. Erosion occurs when the gradient is too steep for the conditions, but the result of that erosion is a reduction in the gradient, which in turn decreases the rate of erosion.
In summary, in this particular context described, while high discharge can contribute to the potential for erosion if the gradient is excessive, the resulting erosion acts to lower the gradient, leading to a decrease in the rate of erosion over time as the stream adjusts towards a more stable profile.
