Chapter 16
Models in hydraulic
engineering
16.1 Hydraulic models
16.1.1 General
Hydraulics and hydraulic engineering have been marked during the 20th
century by an extraordinary development of experimental methods
leading to the widespread use of scale modelsand by the application of
computational techniques.
Although many engineers use the terms mathematical, numerical
and computational model as synonyms, there is a clear distinction between
them. A mathematical modelis a set of algebraic and differential equations
representing the flow and based on assumptions about the physics of the
prototype flow and environmental processes. A numerical modelis an
approximation of the mathematical model in the form of a computable set
of parameters describing the flow at a set of discrete points. The computa-
tional modelis the implementation of a general numerical model for a spe-
cific situation. There are many computational systems available and the
user has to choose carefully among them; this choice requires, or at least is
helped by, the understanding of the underlying mathematical model.
Computational models are often cheaper than the equivalent phys-
ical scale model (see below) and do not suffer from scale effects. On the
other hand they can be applied only where the physics is known and
included in the model and where sufficient topographical and other rele-
vant data are available. Furthermore, their accuracy may be limited –
sometimes severely – by the schematization and discretization procedure
and lack of calibration.
From data handling the discipline of computational hydraulics has
grown to hydroinformatics, which uses simulation modelling and informa-
tion and communication technologies (ICT) to help solve problems in
hydraulics, hydrology and environmental engineering for further manage-