Sedimentary Budget - Feedback Mechanisms

Feedback Mechanisms

In order to understand the sedimentary budget of a coastal environment it is important to know the different types of feedback that can determine whether there is stability. When a beach environment is effected by wind, wave and tidal energy it responds with either positive or negative feedback which determines whether the system is balanced and in equilibrium.

Negative feedback is a stabilising mechanism acting to oppose changes to coastal morphology and establish equilibrium. A coastal environment in equilibrium is able to dissipate or reflect incoming energy without the occurrence of sediment input or output and change to morphology. For example; when a beach in equilibrium erodes during a storm it forms an offshore bar that in turn forces waves to break over it. By doing this the waves lose a lot of energy and dissipate before reaching the shoreline, significantly reducing further erosion. When the storm calms, the bar is then re-worked back on to the beach.

In contrast positive feedback pushes a coastal system away from equilibrium by modifying its morphology until a threshold is reached, whereby a different type of response occurs. For example; if a storm event was to breach the foredune of a beach that is not in equilibrium, a vulnerable area would be created, which in turn would become susceptible to the formation of a blowout due to wind exploiting the absence of vegetation.