In the Channel Stability section, we discussed how stream channels can go through a multi-step evolution following a major disturbance within a watershed. Watershed disturbances can be either human-caused or natural, and can have repercussions well beyond the reorganization of the stream channel. Becoming aware of the potential implications of human actions can aid us in making better-informed land use and management decisions.
Natural disturbances include drought, floods, wildfires, insects, and disease. In many cases, ecosystems can restore equilibrium following these types of events without human intervention. Ecosystems by design are resilient; biological systems have evolved under conditions of periodic droughts, floods, and fires.
In contrast, human alterations to stream channels can have significant rippling effects within stream systems. Dams, constructed for reasons including generating hydroelectric power and storing water, disrupt the natural fluctuations in stream flows and diminish the amount of water reaching the downstream portions of the watershed. Sediment that is transported via the stream is trapped behind the dam and does not reach the downstream portion of the river, affecting hydrology and habitat. Additionally, the temperature of the stream exiting the dam is much lower than the natural stream temperature, threatening biological communities that evolved under warmer stream conditions.
An animation of how stream corridors respond differently to flooding events depending on how they have been altered.