Problem

How does the Travel Time (Tt) affect the runoff hydrograph using the TR-55 method?

Solution

The travel time represents the time runoff takes to travel after it leaves the outfall of a catchment. For example, say the outfall of a catchment is a channel which transfers the runoff downstream. The time in the channel is the Travel Time. The longer the travel time the greater the attenuation and kinematic shift of time to peak of the hydrograph. Leaving Tt = 0 gives you the hydrograph at the immediate catchment outfall point.