Watershed delineation: Inlets and Outlets

[Trigger]

Hi there!

I am still in the beggining working with ArcSWAT and the first step
is the watersged delineation. After I have performed the flow
direction and flow accumulation and created streams and river
junctions the next step is the outlet and inlet definition. According
to the manual of Arc-SWAT the user has to define the inlets and outlet
points by editing manually the points. How am I supposed to know where
are the inlets and outlets in the watershed just by looking on the
DEM. Does anybody know???

Thanx in advance!


Trigger

[Jim Almendinger]

Your "outlet" point is the lowest (farthest downstream) point in the watershed that you want to include in your model.  

If you are modeling the entire watershed above that point, then you will not have any natural "inlets".  I would say this is the most common case.  If you are including some point sources, then perhaps these are also considered inlets, because in a way they are.  

If however, you are modeling only some lower part of a watershed, your "inlet" point would be the uppermost point on the stream to be included in your model.  You might have more than one of these "inlets."  However, you would need to have a complete flow (and water quality if needed) record for each inlet for the entire period to be modeled.  I don't think this is commonly known or done.  

Cheers,

-- Jim

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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/

[Trigger]

I think I confused things a little bit...
The watershed delineation dialog in Arc-SWAT has 5 parameters

1) DEM setup
2) Stream definition
3) Outlet and inlet definition
4) Watershed outlets(s) Selection and Definition
5) Calculation of subbasin parameters

I think you are mentioning about the 4th one which is about the the
whole watershed's outlet.
I was talking about the 3rd one which if I'm not mistaken (according
to the manual of Arc-SWAT) is about the subwatersheds' inlets and
outlets.
I know it's not difficult to determine the outlet of the whole
watershed but how about the outlets of the subbasins???
This is what I don't understand...

Thanx in advance!

Trigger

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[Colin Ragush]

Trigger,

The only time the inlet really is of concern is in the case it is a
point source.

the inlet(s) of a subbasins is/are the subbasin(s) upstream of it.
It automatically consideres these ones and usually isn't a problem.

Don't stress about this part unless you have unaccounted sources or
are having trouble moving to the next step.

Care

Colin

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[Jim Almendinger]

The watershed delineation routine will automatically create the outlets for each subbasin, based on the "critical source area" you specify -- i.e., the threshold level you specify for the minimum size of subbasin.  The smaller this area, the more subbasins ArcSWAT will delineate (and the higher spatial resolution your model will have).  

These outlets are the points at which SWAT delivers its output data -- you may obtain flows and loads at each of these many points.  

Usually, you will want to compare model output with monitoring data from the watershed.  Consequently, you would like to have the locations of your monitoring stations coincide with the outlets that ArcSWAT determines.  To do this, make a table of your monitoring site locations and enter them into ArcSWAT just prior to the subbasin delineation step.  These are "table added outlets."  Then ArcSWAT will not only delineate the subbasins as usual, it will also make sure that an outlet is created at the location of your monitoring stations -- giving you a place where you can compare model output and monitoring data.  (The location of the monitoring stations you give in the table have to be close enough to the stream channel for ArcSWAT to "snap" the point to the channel.)  

-- Jim

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[Behnam Ababaei]

Dear users,

Is there any document on how SWAT ( or other similar mothels ) can delineate subbasins using DEM Map or any programming codes related to this job?

 

Thanks

Behnam

[Trigger]

Behnam,

when you download Arc-SWAT for ArcGIS the folder is included in
that contains the ArcSWAT documentation as a .pdf.
I don't know about other softwares but that's how it is for ArcGIS.

Cheers.

[giannis]

Dear all

1) A suggestion from my experience in using Avswat for years: Just
delineate your watershed with a small number of subbasins if you are a
beginner. It will be easier for you to have a look at the output files
and to understand the results. Additionally, model run will be much
more quick and you can run the model tenths of times per day. If I
used the model for first time I would delineated the watershed with
just two outlets. One subbasin and the total outlet with measurements
available on those sites as well.

As I am also a beginner with ArcSWAT I have also 2 questions and I
would appreciate if someone could help me:

a) why when I push the final button of the watershed delineation
dialog the model crashes when it calculates subbasin geometric
parameters? Unfortunately, I can not continue with the land use
definition as those selections are not becoming active. The model
stops suddenly the operation and the dialog of watershed delineation
appears again with the catchment delineated with the subbasins but
with the parameters calculation being stopped. What would be the
secret here? I'm really very interested in learning because some weeks
ago SWAT calculated the parameters successfully with exactly the same
inputs and in the same PC but now it is unable!!

b) how can I obtain the source code of the model? I know that SWAT is
open source. Where can I download it from please?

Thank you all in advance

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[Naresh]

b) http://www.brc.tamus.edu/swat/soft_model_2005soft.html

On Nov 22, 3:06 pm, giannis <yiannispanagopou...@gmail.com> wrote:
> Dear all
>
> 1) A suggestion from my experience in using Avswat for years: Just
> delineate your watershed with a small number of subbasins if you are a
> beginner. It will be easier for you to have a look at the output files
> and to understand the results. Additionally, model run will be much
> more quick and you can run the model tenths of times per day. If I
> used the model for first time I would delineated the watershed with
> just two outlets. One subbasin and the total outlet with measurements
> available on those sites as well.
>
> As I am also a beginner with ArcSWAT I have also 2 questions and I
> would appreciate if someone could help me:
>
> a) why when I push the final button of the watershed delineation
> dialog the model crashes when it calculates subbasin geometric
> parameters? Unfortunately, I can not continue with the land use
> definition as those selections are not becoming active. The model
> stops suddenly the operation and the dialog of watershed delineation
> appears again with the catchment delineated with the subbasins but
> with the parameters calculation being stopped. What would be the
> secret here? I'm really very interested in learning because some weeks
> ago SWAT calculated the parameters successfully with exactly the same
> inputs and in the same PC but now it is unable!!
>

> b) how can I obtain thesourcecodeof the model? I know that SWAT is
> opensource. Where can I download it from please?

[Latha Baskaran]

Regarding problem a) - I once had the same issue. SWAT kept crashing
at the stage of calculating the subbasin parameters. This happened
even with the example dataset. It turned out to be a space issue on
my PC. I had 5GB of free space on my PC and that wasn't enough. I
freed some more space (20GB or so) and I was able to get rid of the
problem!

Hope this helps.