WMS:TR-55 Sheet Flow Equation

Sheet flow generally occurs in the headwater of streams. The following equation is used to describe sheet flow:

File:WMSEqation132.png

where:

</math>T_t</math> = travel time (hr).

</math>n</math> = Manning’s roughness coefficient (see Table 3-1 of the TR-55).

</math>L</math> = flow path length (ft).

</math>P2</math> = 2year, 24 hour rainfall (in).

</math>s</math> = slope of the hydraulic grade line (ground slope) in ft/ft.

2 year, 24 hour rainfall values can be determined from the map in appendix B-4 of the TR-55 reference manual for eastern US locations and from the NOAA Atlas 2 maps for the western US locations.

Generally the sheet flow equation should not be used for lengths greater than 300 feet.

Related Topics

• Overview of Map Data Equations