[GRASS-user] help with r.gwflow

[Vishal Mehta]

Thanks Soren,
for your script.

i'm using r.gwflow in v6.5svn, which does not have the budget parameter
option. do you know how i can get the 7 version to work in my 6.5 version?

also, i'd like to know how all th rest if it is set up - the river_bed
parameters etc. do you have complete documentation of it? i'm trying to
model the coupled water supply-extraction and groundwater system of a city,
so more complex real world examples of the use of r.gwflow would be really,
really useful. have you used it in a ocomplex setting perhaps for your
dissertation?

thanks again,
Vishal

On Wed, Jul 18, 2012 at 2:47 PM, Sören Gebbert <soerengebbert at googlemail.com
> wrote:

> Hi Vishal,
>
> 2012/7/18 Vishal Mehta <vishalm1975 at gmail.com>:
> > hi Soren,
> >
> > my constan head boundary conditions on the edges are causing water
> tables to
> > build up everywhere else. so i estimated a constant flux 0f 0.0019 m3/s
> that
> > i want to apply for edge cells. this is what i am trying in order to
> impose
> > a constant flux on the edges
> >
> > r.mapcalc "sink.init=if(row()==1 || row()==444 ||col()==1
> > ||col==477,-0.0019,null())
> >
> > #sink.init is the constant flux on edges
> > # my r.gwflow script runs at monthly time step- ihave a loop
> $month-here's
> > the r.gwflow snippet
> >
> > r.gwflow --o -s solver=cg top=top bottom=bottom status=bc2 hc_x=k.1
> hc_y=k.1
> > s=s.1 type=unconfined dt=2592000 error=0.05 phead=sim.$((prevmonth))
> > r=gwnaturalms.$((month)) q=sink.init output=sim.$((month))
> >
> > my boundary condition map (bc2) has contant head in strea pixels. all
> else
> > are calculated.
> >
> > do you think the above implementation will correctly impose the constant
> > flux on the edges? it seems though that since this is not a boundary
> > condition, how can it ensure a constant flux at edges?
>
> Your script looks reasonable, except that the error term is much to large.
> You may need to use a smaller number like 10⁻7,
> otherwise your results my be wrong.
>
> I have attached a small r.gwflow example to show you how to estimate
> the constant flux at
> a western boundary using the budget computation. Since the flow will
> be specified
> as a source term, it will be constant the whole computational time.
>
> Maybe you can apply this method to estimate the boundary flux in your area?
>
> JFYI i am using r.gwflow of GRASS 7.
>
> Best regards
> Soeren
>
> >
> > Thanks for any help you can provide,
> > Vishal
> >
> > On Mon, Jul 16, 2012 at 1:46 PM, Vishal Mehta <vishalm1975 at gmail.com>
> wrote:
> >>
> >> Thanks Soren,
> >> From you response, can you please tell me how to do the following two
> >> tasks (which i dont find in the online manual for r.gwflow): the
> remainder
> >> of your comments i have figured out.
> >>
> >> - How can i compute the flux in [m^3/s] for each cell with r.mapcalc?
> >> and
> >>
> >> - i have set the bc of the edges and stream cells at constant head for
> >> now- how can i get the budget raster maps you mention?
> >>
> >> thanks again,
> >> Vishal
> >>
> >>
> >> On Sat, Jul 14, 2012 at 12:05 PM, Sören Gebbert
> >> <soerengebbert at googlemail.com> wrote:
> >>>
> >>> Hi,
> >>> sorry for the delay.
> >>>
> >>> 2012/7/11 Vishal Mehta <vishalm1975 at gmail.com>:
> >>> > Thanks Soren,
> >>> > That explains some of the results i'm getting, with water piling up
> >>> > above
> >>> > the surface in the edges in low-lying areas.
> >>> >
> >>> > Can you please tell me how i can change that to constant flux or
> >>> > constant
> >>> > head? If constant flux, should that be in m/s units?
> >>>
> >>> Constant flux can currently only be defined using sources/sinks with
> >>> unit [m^3/s], that is option q.
> >>> But i can add two new options (fn, fe) that defines the flux in
> >>> northern or eastern direction using the unit [m/s]
> >>> that will be multiplied internally with the northern or eastern face
> >>> area of the cell?
> >>>
> >>> Otherwise you need to compute the flux in [m^3/s] for each cell with
> >>> r.mapcalc.
> >>>
> >>> >
> >>> > My problem though is that i dont know what a constant flux or head at
> >>> > the
> >>> > edges should be set to. For now the only bc i have put in there
> >>> > deliberately
> >>> > (beyond the default you mention) is that i have set constant head in
> >>> > stream
> >>> > pixels. I'll have to let flow through at the edges but i have no idea
> >>> > what
> >>>
> >>> You can use the river boundary condition to specify the flux in stream
> >>> pixel.
> >>>
> >>> > that flow should be. Are there some ways of setting the edge
> conditions
> >>> > such
> >>> > that the gw evolution in the central areas of interest are not highly
> >>> > influenced?
> >>>
> >>> You can set the boundary of interest to constant head pixel and
> >>> compute the flow throw the boundary pixel using the budget option.
> >>> The resulting budget raster map shows the flow from active cell into
> >>> sources, sinks and constant heads in [m^3/s].
> >>>
> >>> Best regards
> >>> Soeren
> >>
> >>
> >>
> >>
> >> --
> >> Vishal K. Mehta, PhD
> >> Scientist
> >> Stockholm Environment Institute - US
> >> 133 D St Suite F
> >> Davis CA 95616
> >> www.sei-us.org
> >
> >
> >
> >
> > --
> > Vishal K. Mehta, PhD
> > Scientist
> > Stockholm Environment Institute - US
> > 133 D St Suite F
> > Davis CA 95616
> > www.sei-us.org
>



-- 
Vishal K. Mehta, PhD
Scientist
Stockholm Environment Institute - US
133 D St Suite F
Davis CA 95616
www.sei-us.org
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