[GRASS-user] help with r.gwflow

[Vishal Mehta]

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?

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20120718/1f7b22fa/attachment.html>