Environmental Engineering Reference
In-Depth Information
Fig. 5.1
Relative contributions of
interpretational and analytical approaches in
different tools in the FRMRC Sediment
Toolbox. CAESAR, Cellular Automaton
Evolutionary Slope and River Model; HEC-RAS
Sediment Transport (ST), Hydrologic
Engineering Center River Analysis System;
REAS, River Energy Audit Scheme; SIAM,
Sediment Impact Analysis Method.
In deciding whether further reductions in un-
certainty merit the expenditure of time and re-
sources necessary to achieve them, it is prudent to
consider the level of risk stemming from the un-
certainty. In some cases, uncertainties may be
large, but may pose little risk to the outcome of
a proposed project. Attempts to further reduce
uncertainty through additional data collection or
use of a higher accuracy model are justified only if
the risk associated with the current level of un-
certainty is too high to allow the project to pro-
ceed. In this context, according to Brookes and
Dangerfield (2008), the level of uncertainty should
be assessed as being:
.
Unacceptable: risks associated with existing
uncertainties cannot be tolerated and further ef-
fort must be made to reduce them at least to a
tolerable level and ideally to an acceptable level.
.
Tolerable: the risks associated with existing
uncertainties are significant but can be lived with
and effort to reduce uncertainties further would be
disproportionate to the risk reductions achieved.
.
Acceptable: the risks associated with existing
uncertainties are insignificant.
It follows that, when selecting a sediment anal-
ysis tool and designing the data collection cam-
paign to support it, the target should be to reduce
uncertainties to the level at which they are ac-
ceptable or, at least, tolerable, recognizing that it is
impossible to eliminate them entirely.
This approach requires consideration of all the
various risks associated with sediment and its
analysis, including those related to the nature of
the problem being investigated, the physical en-
vironment, the objective of the modelling inves-
tigation, and the time, human resources and
money available to support the work. The fact is
that time, human resources and money will al-
most always limit the levels of detail and com-
plexity that can be included in the study and the
