In addition to the full hydrodynamic solution techniques Flood Modeller also includes flood routing methods. Flood routing is used here to describe the process of determining the change in shape of a flow hydrograph as it moves along a channel without necessarily calculating water levels. Both the Muskingum and the Muskingum-Cunge flood routing methods are available and velocities can be estimated as a user-defined function of flow, for use in the Flood Modeller Water Quality model.
A particular feature of flood routing facility is the ABSTRACTION unit. This unit can act as a flow boundary or can be placed between a JUNCTION or RESERVOIR and flood routing units. It allows the user to specify rules for abstraction of water or reservoir operation. These rules may specify the abstraction or flows as a function of variables defined at any node in the model so that, for example, abstracted flow could be specified as a percentage of the base river flow. At each abstraction, a number of logical rules defined by Fortran-like 'if statements' may be specified and these rules can be applied as a time series. In this way the effects of abstraction licences with seasonal variations can be modelled.