Comparision of Arc SWAT and Hec HMS

[cva shrestha]

Dear all

Can anybody help me find out which among these two can provide
better results
one of friend using hec hms had over 90% efficiency
and in swat i got only 80%.Does that mean swat is not good as hec hms..hec hms can take discharge data as input and swat cannot.so snow data from remote sensing couldnt be fed into swat ,,is there any technique for this.
Whats the efficiency SWAT can provide  ?

Also,other models calculate precipitation using Thiessen etc.
Whats in the case of SWAT

Thank you
Shiva

[Kyle]

Shiva,
I wouldn't say that SWAT or HEC HMS is better than the other. Each
model has its strengths and weaknesses. Some watersheds perhaps you
can get better results with one model over another. Sometimes a user
is simply better at using one model versus another.
As mentioned in the previous response, if you want to add discharge
flows from a soure, you can incorporate a point source or an inlet
flow depending on the location (inlet would be coming from outside the
watershed, point source can be used within the watershed). I know
there are tools available for incoroporating radar-derived
precipitation into SWAT. The name of the tool escapes me at the
moment, but I'd bet if you do some Google searching with key words of
SWAT (or soil and water assessment tool) with radar, you'll probably
run across it. Perhaps another person can answer from the group.
In regards to the efficiency SWAT can provide, it really depends on
the situation. The quality of data and the efficiency of the user can
greatly affect your results.
Precipitation in SWAT is generally input by the user. You can add as
many weather stations as you have available, and SWAT will assign
precipitation for each subbasin based on the weather station that is
closest to that subbasin's centroid. Again, I'd refer to the SWAT
documentation for details on how SWAT handles precipitation. It is
covered in much more detail than you will get here.
Regards,
Kyle

[zorba_cva]

kyle
Thanks a lot.
To make you more clear in what i am stuck into.
1.From remote sensing we can develop shapefiles of snow and using TANK
model
the discharge can be found out..now the question is how will the swat
model the flow(routing procedures)..i m
happy with your answer that swat can take it by point input
discharge..
2.There are two routing methods in swat.i wanted to know what does is
opts for?i couldnt find it,
3,your answer about hec hms and swat is convincing..however i am
confused abt which is better...which to prefer and when???
4.My question on precipitation...is averaging techniques like thiessen
better or the one that swat follows..during my hydrology classes
i always was suggested inversed distance relations...
Thanks again
Shiva

[Kyle]

Shiva,
1. I guess I'm unclear on what you mean in terms of how SWAT will
handle this. I'm envisioning that you will have your shapefiles with
the snow pack, and you would have discharge (flow contribution) from
these snow areas. You'd have to break it up into your subbasins, and
add a point source in each subbasin where you are going to contribute
that flow. In your precipitation files, you'd want to make sure
precip is set to 0 as to not double your snow contributions. As far
as being routed into your stream reaches, I believe SWAT would simply
"dump" that contribution from the point source into the beginning of
the reach where it would be combined (and mixed) with the upstream
flow contributions (if any), and these would all be mixed together and
routed downstream. If you have more questions as to the processes of
the routing, I would suggest looking at the Theoretical Documentation
(check 2005 version since I don't believe 2009 is on the SWAT website
yet), or you can hope that someone else can describe in more detail
than I did. As far as using your method that you outlined above, does
your TANK model account for sediment or nutrient loading accompanying
your flow? If SWAT has zero precipitation, it isn't going to erode
anything off your landscape (although in channel erosion/deposition
would still occur). I would just keep this in mind depending on the
scope of your work.

2. Are you looking for a description of Muskingum versus Variable
Storage? If so, go to the Theoretical Documentation (2005 version
most likely).

3. I'm not sure which model is preferable in different situations.
The SWAT website has a "Publications" link on the top of their main
webpage. There are options for finding different professional
publication articles. I would guess somewhere there is an
professional paper describing the differences between the two models.
Or maybe someone else can jump in on this conversation. I don't have
enough experience with HEC-HMS to give you a good opinion.

4. When it comes to precipitation, it'd be hard for me to give a
preference of one technique over another. To me, the most important
factor is the number of precipitation observations that you can find.
The more rain gages you can have, the better off you will be. The
nature of precipitation events makes it very difficult to accurately
interpolate actual precipitation. A storm event could be very
localized over a precipitation gage, and regardless of the averaging
technique, they can simply be wrong if there was no precipitation
across the rest of an area. Precipitation accuracy is always an issue
that you just need to account for when reporting results. There are
going to be rain events missed or rain events that will cause
precipitation to be over-estimated in your watershed, regardless of
your technique. One potential solution is to use radar-based
estimation. The intensity of rainfall measured by radar can allow for
an estimate of total rainfall at a given location. This remote
sensing technique can help to fill in those gaps. How accurate is
it? I don't know off the top of my head, but it is another option
that you can try and research.

I hope this helps.
Regards,
Kyle

> > > Shiva- Hide quoted text -
>
> - Show quoted text -

[Johanson, Christopher]

I used HEC HMS in a Hydrology Engineering class I took a while back, and as I recall, HEC HMS was very focused on flow, and approached it from an engineer's 'worst case scenario' point of view.

SWAT on the other hand, models a lot more stuff: sediment, nutrients, pollutants, etc. It simulates more complex land use and management processes (different crops, agricultural practices, filter strips, street sweeping, etc) and more complex in-stream processes. I think SWAT can take larger amounts of complex inputs that HEC HMS ignores.

So it depends upon what you are trying to model and what results are important.

CJ Johanson

________________________________________
From: arc...@googlegroups.com [arc...@googlegroups.com] On Behalf Of zorba_cva [istanda...@gmail.com]
Sent: Friday, April 08, 2011 10:27 AM
To: ArcSWAT
Subject: [ArcSWAT:3300] Re: Comparision of Arc SWAT and Hec HMS

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