WMS:TR-55 Outlet Data

The TR-55 dialog showing outlet data

WMS allows defining the watershed as a single basin or subdivide the watershed into multiple sub-basins. Besides computing peak flows using the standard TR-55 equations, storm hydrographs may also be computed for each basin and then combined/lagged to downstream outlets (junctions) using the TR-55 tabular hydrograph method.

When creating a watershed with multiple sub-basins, define the time of travel from one outlet (junction) to the next. The travel time for an outlet is defined by selecting the outlet and then entering the appropriate travel time. If desired, use a time computation arc to compute the travel time.

• Outlet Name

The Outlet Name is used to identify individual outlets within a larger watershed. As with all outlets created in WMS, the name is defaulted to “ID”R where ID is an internal identification number and R stands for outlet. The name can be changed to something more identifiable at any time. While TR-55 does not require that outlet names are unique, other models supported by WMS do.

• Travel Time

The TR-55 travel time is the amount of time a flood wave takes to move from the outlet to the downstream most point of the watershed. This is different than other models in WMS which enter the travel time from outlet to outlet. Computed hydrographs at each basin and each outlet point represent the amount of the hydrograph at the outlet point contributed from each basin or each outlet point. Thus, the hydrographs are already lagged when running TR-55 in WMS. The upstream hydrographs are then simply added together to determine the hydrograph at the watershed outlet point. No lagging is done in WMS; tabulated TR-55 hydrographs are pre-lagged.

Like time of concentration, travel times between outlets may be computed using a series of feature objects with equations such as Manning’s defined for each.

• Compute Travel Time
• Compute Hydrograph

Related Topics

• Channel Travel Time
• TR-55 Overview
• Basin Data
• Hydrographs