outxx.out file - saveconc

[Colline]

Hello,

a small question about the output files created by the option :
saveconc.

Are the results suppose to be the same than the corresponding
subbasins in the output.rch?

For example for the same subbasin : Sed_out of the output.rch
shouldn't be the same than Sed of the ouxx.out file ?
I compare this two columns (with unit conversion that this comparison
requires) but find some slight differences or even big ones which can
go up to 5 Tons.

Any clue why. Which file should I use to study water quality and
sediments and nutrients loss in my Watershed. Do you know a documents
explaining this file a little bit more than the Input_Output manual
file?

Thank you in advance for your answer!

Colline

[Marylee Murphy]

Hello SWAT users,

I am modeling a small (500 ha), mixed land use watershed in Minnesota
and am having a problem where about 100 kg per year of phosphorus that
has been transported from the landscape settles in the stream
(Calculated from the .rch file as (ORGP_Inkg - OrgP_Outkg) + (MinP_Inkg
- MinP_Outkg) ). This is nearly half of the phosphorus exported from
the landscape in low-flow years. I have the stream water quality
inactive and the Aglae/CBOD/Dissolved Oxygen simulation inactive. I
experimented with the SPCON and SPEXP parameters and they did not alter
the settling. Has anyone else noticed this and does anyone have any
idea which parameters control this channel phosphorus deposition?

Thanks,
Marylee
--
Marylee Murphy
Water Resources Specialist
Three Rivers Park District
12615 County Rd 9
Plymouth, MN 55441
763-694-2048

[Jim Almendinger]

Marylee --

I'm pretty certain that you're right, that SPCON and SPEXP control sediment deposition only, which is entirely separate from phosphorus deposition in SWAT (they are of course coupled in reality).  

If I recall, P deposition in channels in SWAT is controlled principally by a settling or deposition parameter within Qual2e -- and if Qual2e is turned off, then P isn't lost to the channel.  In the old AVSWAT interface to swat2000, I noticed that the radio buttons to turn on/off the stream and lake water-quality routines appeared to be reversed -- but you probably know this, and in any case this should've been fixed in the new ArcSWAT interface.  It'd be worth checking your txtinout input files to make sure Qual2e really is inactivated (there's a parameter that serves as a flag in one of the control files).  Again, I suspect you checked this.  

I suppose excessive transmission losses could result in P losses in the channel.  Seems unlikely.  

I suppose I'd check the subbasin output of P, to see if it matches the total input to the channels in the Reach file (you'd have to be careful not to double-count what is being passed downchannel).  Simplest would be to look at a few headwater subbasins separately, to see how subbasin outputs matched reach inputs, and then reach outputs.  

But -- unless Qual2e is accidently turned on, I don't have an answer.  The channel should not be depositing phosphorus unless you activate Qual2e and have a positive settling rate and a non-negligible phosphorus content per algal body.  

Please -- if others spot something I've missed, let us know. 

Cheers, 

-- Jim

Dr. James E. Almendinger, Senior Scientist

St. Croix Watershed Research Station

Science Museum of Minnesota

16910  152nd St. N

Marine on St. Croix, MN  55047

tel: 651-433-5953 X 19

fax: 651-433-5924

email: din...@smm.org

web: www.smm.org/SCWRS/