Environmental Engineering Reference
In-Depth Information
Although both morphological and cascading systems are convenient conceptual models
which aid an understanding of processes occurring in the landscape, they are clearly
approximations to the many complex interrelationships which occur between inputs,
outputs, flow and the morphological structure. This set of connections between the
throughput of energy and matter on the one hand, and morphology on the other, is best
explained in the third type of system, the
process - response system
, which emphasizes
the relationships between process and form. Thus Figure 1.6 illustrates the process - form
relationships between the slope subsystem of the valley sides of Upper Wharfedale and
the channel subsystem of the river Wharfe. The relationships between the processes and
their responses are shown again by positive and negative controls. An increase in slope
erosion will lead to an increase in stream bed load, which in turn causes a decrease in
channel erosion, and eventually a decrease in valley-side slope angle, and ultimately a
decrease in slope erosion.
The 'knock-on' effects of change within any process - response system take the form
of
feedback
loops. Feedback refers to 'the feeding back of part of the output of a system
as input for another phase of operation, especially for self-correcting or control purposes'
(Chorley and
Figure 1.5
The cascading system of slope hydrology.
Kennedy 1971).
Negative feedback
acts in a conservative manner, by which a change in
the cascade produces morphological changes which create variations in the cascading
system, leading to a damping down of the effects of the original change. In short,
negative feedback slows down the rate of change.
Positive feedback
occurs when closed
