WHY USE STA?

It is the only method to know how an environment is working. In Situ measurements may provide some information and such data are often used in numerical modeling. Neither, however, provides the understanding that is achieved by STA.

Factors for considerationSTAIn Situ MeasurementsNumerical Models
Ability to extrapolate
over a large region
Can be carried out on any scalePoint location measurements onlyDependant on database
Instrumentation required

None

Instrumentation essential and subject to lossProcess data required as model input
Assumptions

None required
Assumptions must be made for best site locations and variables
Must assume what processes are operating
Incorrect or biased
results

No bias possible. The sediments provide the data that integrate all processes
Quite possible; all processes cannot be measuredQuite possible; operating processes may be incorrectly assumed
Validation
Entirely self-validatingValidation self-evidentConvincing validation often difficult
Defensibility of results

The grain-size data cannot be refuted

The chosen variables may not account for net sediment transport
Results may be 'tweaked' to provide more than one answer
Future problems resulting in unexpected expenses
In over 25 years, recommendations from an STA analysis have never been wrongIn situ measurements are frequently insufficient to determine net sediment transport
There are many examples of costly mistakes based on numerical model predictions