Hi Vishal, 2012/7/18 Vishal Mehta <[email protected]>: > 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 <[email protected]> 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 >> <[email protected]> wrote: >>> >>> Hi, >>> sorry for the delay. >>> >>> 2012/7/11 Vishal Mehta <[email protected]>: >>> > 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
groundwater.sh
Description: Bourne shell script
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