Which type of scour is associated with short-term changes in downstream water elevation?

The correct type of scour associated with short-term changes in downstream water elevation is general scour. This phenomenon typically occurs when there are fluctuations in flow that can lead to erosion of sediment in the riverbed, often as a result of changing hydraulic conditions such as increased discharge or altered flow patterns. General scour affects a larger reach of the riverbed and is primarily driven by the overall energy of the water flow, making it responsive to rapid changes downstream.

Other types of scour include live-bed scour, which occurs when sediment transport is happening both upstream and downstream, and this is influenced by the sediment size and flow conditions. Clear-water scour refers to conditions where sediment is removed from the bed without significant transport downstream, and this typically occurs when the flow is below the threshold for sediment transport. Contraction scour is related to the constriction of flow, which can increase water velocity and cause erosion near bridge piers or other obstructions. While these other types of scour have specific conditions associated with them, general scour is particularly responsive to short-term hydraulic changes, making it the correct answer in this context.