Dodson (Dodson & Associates, 1992) compiled several equations from hydrologic publications. WMS has implemented many of these equations and allows you to choose from the ones listed below to automatically compute lag times/times of concentration. Because most of the equations were developed for specific watersheds (e.g. size, land cover etc.) you should consider the assumptions made about a given equation, and try to identify one that used watershed conditions similar to the one you are studying. The following is a list of the equations available in WMS. The SCS also found that for many cases the lag time could be related to the concentration time by the following equation:
This relationship is always used by WMS to determine lag time when a method for computing time of concentration is chosen, or to compute time of concentration when a method for lag time is chosen. Methods used for lag time begin with “TLAG =“ whereas methods used to compute time of concentration begin with “tc =“.
Lag Time Based Equations:
Colorado State
Customized
Denver
Eagleson
Espey
Putnam
Riverside County
SCS
Taylor Schwartz
Tulsa District
Time of Concentration Based Equations:
Fort Bend
Kerby
Kirpich
Ramser
Related Topics:
Travel Times from Basin Data
Travel Times from Map Data
Assigning an Equation