hydrograph 2

[engrsalah]

Respected
i want to know if i have two hydrograph of rainfall 15 minutes interval and 1 hour interval and correspondingly the same for hydrograph (15 minut and 1 hour respectively) which one will have the peak flood. 15 minute hydrograph or 1 hour hydrograph?

 

[beej67]

If I understand your question properly, it depends on the watershed.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[engrsalah]

Respected beej67
i little elaborate the question as follow.
i have a rainfall event for 24 hr. and i want to construct two flood hydro graph. if i use time interval 15 minute for one hydrograph and 1 hr for second hydrograph. having the same catchment. which one will have the peak flood. 15 minute hydrograph or 1 hour hydrograph?

 

[psmart]

In general, the hydrograph with the smaller time increment will produce a higher peak flow which will be a better representation of the true instantaneous peak. As you increase the hydrograph time step, the peak flow will be understated because each point is an average over a longer time period. A general rule of thumb is to use a time step that is less than one-half the time-of-concentration.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[beej67]

There are some softwares which will give you bogus results if your calculation time increment is not a multiple of the time increment in your hyetograph. I believe HEC-HMS used to be this way, although it's been a long time since I used it. So consider that.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com