...
Piecewise routing allows you to specify how K varies with flow. If x=1, then K must always be less than or equal to the time-step. In BigMod routing, the highest value of K is found in the travel time relationship, and the reach should be sub-divided into sufficient divisions such that the highest value of K for each division is less than the half the time-step.
...
Link rating curve
Rating curves are used to describe the physical characteristics of the reach and convert a flow into a level, ie. they produce an output of level. They can be specified in one of two ways:
...