My question is: how to do groundwater interpolation (I have data from 71 wells) with respect to DEM.
I mean when I do interpolation without respect to DEM my groundwater level is above terrain level, so how to get rid of this problem?
your groundwater levels can be converted to height above mean sea-level or depth below the well casing (negative amounts) and these values will be used in the interpolation.
If I am reading this correctly, it sound very similar to an exercise I have used with our local college. Basically what you are needing to do is calculate the elevation at the bottom of your wells?
the red circles in the graphic above.
Providing you have a well attribute of depth?
Extract the surface value from the DEM (Extract Values or Add Surface Information tools) . Then calculate the well bottom elevation by subtracting well depth from well surface value. Example; well surface is located at 5,900 ft and the well depth is 200 ft - well bottom is 5,700 ft.
Use those calculated well bottom values to create (interpolate) a 'rudimentary' ground water surface that should fall below the DEM surface.
Thank you for your answers.
I have data from 71 wells with information about water table depth (I "changed" these depths to heigh above sea level).
I need to calculate water table elevation, but my water table still somewhere is above the terrain level (my area is muntains and scale is 10:000).
I rather need some interpolation with barriers (?) where my barriers would be terrain level from DEM (or contours from DEM).
If I'm understanding you correctly, your groundwater surface is above your land surface, likely in the valley areas of your terrain domain. Is there water running in these valleys? If so, is it clear that there is a groundwater connection to these streams? If so, these streams can be used as additional data "points" (lines actually) for your interpolated groundwater surface. I am not sure what tools or settings you are using for your interpolation, but, in the past, I have:
1) traced the thalweg of the stream,
2) converted the lines to closely spaced points (Construct Points under Editor tools),
3) attribute the points with a Z value derived from the terrain surface (Add Surface Information),
4) and included the new points in the input for the interpolation.
It will likely take some trial and error to get the raster shaped the way that you have interpreted the water table.
Another word of warning - If your end-goal is groundwater contour lines, you will likely still need to manually edit the lines based on your interpretation of the data. Typically what I'll do is attempt to interpolate and model the groundwater surface, then manually edit the contour lines to fit my interpretation. At that point, I use those manually edited contour lines to create a raster that is true to my interpretation..... then scrap everything else.
Hope this helps.