[GRASS-user] help with r.gwflow

[Sören Gebbert]

Hi,

2012/7/19 Vishal Mehta <vishalm1975 at gmail.com>:
> 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?

Unfortunately the grass7 version of r.gwflow does not run in grass6.5
and i have no plans o back port the budget feature.
So maybe you would like to switch to grass7 to compute the budget?

> 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

You need three parameters to model the river:
1.) The water table of the river in [m], mostly derived from a river
vector map and converted into a raster map
2.) The bed of the river in [m], mostly derived from the river water
table: r.mapcalc "river_bed = river_table - 2"
3.) The leakage coefficient of the river bed in [1/s]

River table, river bed and leakage are occupying the same pixels.

Simple and stupid example:

# River with a water table of 20m and the bed at 18m with a
# leakage coefficient of 0.0001 1/s

# First convert the stream network into a raster map
v.to.rast input=streams output=streams type=line

# Then compute the water table of the river at 20m
# and the height of the bed that is 2m lower than
# the water table of the river
r.mapcalc "river_head = if(isnull(streams), null(), 20)"
r.mapcalc "river_bed = river_head - 2"

# The river leakage coefficient can be computed from the hydraulic conductivity
# of the river bed (0.0001m/s) and the thickness of the river bed (1m)
r.mapcalc "river_leakage = if(isnull(streams), null(), 0.0001/1)"

> 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?

The only documentation that is available is the r.gwflow manual page
and my diploma thesis [1] (in German)
that describes the mathematical details. I never utilized r.gwflow to
compute large complex real world problems.

Best regards
Soeren

[1] http://www.hydrogeologie.tu-berlin.de/fileadmin/fg66/_hydro/Diplomarbeiten/2007_Diplomarbeit_Soeren_Gebbert.pdf

>
> 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