Environmental Engineering Reference
In-Depth Information
Fig. 5.2
Balancing cost and risk when selecting a model appropriate for a sediment study.
extent to which model calibration and validation
can be performed. In this context, Overton and
Meadows (1976) stated that:
models is therefore vital when selecting the level
of model complexity appropriate to a particular
sediment investigation and analysis (Fig. 5.2).
In assembling the methods and models to be
included in the FRMRC Sediment Toolbox, the
issues raised in the quotation from Overton and
Meadows (1976) explain why a range of tools,
extending from a very simple treatment of the
sediment transfer system that is easy to apply
(Stream Power Screening Tool) to an advanced,
transport model that routes sediment by size frac-
tion, but is costly, expertise intensive and time-
consuming to apply (iSIS Sediment), was included.
The premise here is that a risk-based approach to
selecting the tool appropriate to the application is
only possible provided that a suite of approaches
that cover a wide range of complexities and fund-
ing situations is available to end users.
'
...
if a highly complex mathematical representa-
tion of the systemunder study is made, the risk of
not representing the system will be minimised,
but the difficulty of obtaining a meaningful solu-
tion will be maximised as much data will be
required, and mathematical handling in a com-
puter model (e.g. convergence and consistency)
and complexity of mathematical processes may
even render the problem formulation intractable.
Further, the resource constraints on time,
(hu)manpower and budgets may be exceeded.
Conversely, if a greatly simplified model is select-
ed the risk of not representing the physical system
will be maximised, though the difficulty in ob-
taining a solution will be minimised.'
Careful consideration of the balance between
the risks associatedwith uncertainty in represent-
ing the behaviour of the sediment system reliably
and the rising costs associated withmore complex
Stakeholder issues
The technical strength and veracity of a tool are
two of a number of criteria that affect its utility
