Drainage areas do not add up?

[ftroop82]

I have two subcatchments DA1 & DA2 , DA1=4.97 cfs and DA2=6.44 cfs, I have both areas routed thru a link to give a combined flow offsite, but the link, gives a total of 8.66 cfs. The total flow should be 11.41 cfs offsite.

 

[ftroop82]

I know the Tc changes to info, but is there a way to add these up to show a total pre flow off of a site? These two areas flow off in two different areas, but Ineed to show a total for the entire site.

 

[TerryScan]

I'm confused by your two posts.

If you are routing the areas together, and the Tc is not the same, the combined peak flow will NOT be a simple addition of the two peaks. It will be the maximum of adding together the flow rates AT EACH TIME INCREMENT.

If the areas are flowing to different locations, I can't understand why one would be adding them up at all. In my locale, one cannot exceed pre flow rates at each runoff location. Not total site. That would be dangerous.

For example, pre Area A had a 1 cfs rate, and Area B had a 99 cfs pre rate...and post Area A had a 90 cfs rate and Area B had 8 cfs...one would be complying with a reduced overall rate, but very likely causing problems at A (1 cfs -> 90 cfs).

If you still only need the simple total of peaks...just write them down...add them up and submit them.

 

[ftroop82]

I just added the areas up and submitted the information in a brief summary.

Thanks

 

[psmart]

Peak flows will add directly ONLY if the peaks occur at the exact same time. To see the addition at each time increment, right-click the tabular hydrograph report and select "Inflows".

The combined volume, on the other hand, should always be the exact sum of the individual hydrographs.