Why will a drop in sea level change the grading of the river?
A drop in sea level can potentially change the grading of a river due to several interrelated factors:
Base Level: Sea level serves as the base level for rivers. When sea level drops, the base level also drops. Base level is the lowest point to which a river can erode its channel. A drop in sea level essentially lowers the point where rivers discharge into the ocean. This can lead to increased erosion downstream as the river attempts to adjust to the new base level.
Gradient Adjustment: Rivers seek to attain a gradient that allows them to transport sediment efficiently. With a drop in sea level, the gradient of the river may need to adjust to maintain equilibrium. This adjustment can result in increased erosion in some areas and deposition in others, altering the grading of the riverbed.
Sediment Transport: Rivers transport sediment from their source to their terminus (typically the ocean). A drop in sea level can affect sediment transport patterns by changing the energy levels within the river system. This alteration in energy can lead to changes in sediment deposition and erosion, ultimately influencing the grading of the riverbed.
Channel Morphology: Changes in sea level can impact the overall morphology of a river channel. This includes changes in channel width, depth, and shape. As sea level drops, rivers may widen and deepen their channels to accommodate changes in sediment transport and water flow, leading to alterations in the river's grading.
Erosion and Deposition: A drop in sea level can expose previously submerged landforms and sediment deposits. This newly exposed material can contribute to increased erosion as rivers adjust to the changed conditions. Conversely, areas that were once underwater may experience deposition as sediment settles out of the water column
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