For discharges close to critical or supercritical flow, and for very short reaches (with time step constraints), SHIFT HYD can be used. Comparisons with the kinematic wave method show that, for a circular conduit, the time lag can be selected with the relation:

Time lag = reach length / (alpha – full pipe velocity)

where alpha is given by the following table:

0.40 1.10
0.60 1.17
0.80 1.19
1.00 1.11