stream flow values in Output.rch

[GT]

I have the "output.rch" from my SWAT model output. This Output.rch has stream flow values for all sub-basins of the whole watershed. My understanding of the reach in SWAT is the main channel but I am confused why the stream flow  for each sub-basin decrease towards downstream even if the sub-basin area also increase towards the outlet of the watershed. 

For calibrating my SWAT model for the whole watershed with different sub-basins stream ( reach) flow values which stream flow value will use? is that the sum of all sub-basin stream flow or the stream flow of the downstream most sub-basin value?. If the reach in SWAT is the main channel the flow output for whole watershed should be represented by the downstream most sub-basin since SWAT uses routing method but I am confused by output of SWAT as I explain above. 

I will be grateful if someone give me more idea on which stream value ( sum of all sub-basin or downstream most sub-basin) value will use for calibrating my whole watershed.

[robert sowah]

Hi There,

if you want to calibrate the entire watershed then you will need to use the discharge from the  outlet you specified to delineate the watershed. this is not to say that you can not calibrate output from a subbasin, but as i understand you are looking to calibrate the entire watershed so i would suggest you use the outlet in the downstream subbasin, provided you have observed data at the outlet for calibration purposes. hope this helps

Robert