If the contours represent the landscape accurately, our results are useful. If not, it may be necessary to smooth the DEM so that slopes will be more accurate. The slope map below shows how sensitive slopes are to the spacing of the contours.
The contours are not evenly spaced. (See the map and profile below.)
If the contours represent the landscape accurately, our results are useful.
If not, it may be necessary to smooth the DEM so that slopes will be
more accurate. The slope map below shows how sensitive slopes are to
the spacing of the contours.
setenv GRIDALLOCSIZE 400
arc
Arc: shapearc contour.shp contour
Arc: topogrid dem 1
contour contour elevation
datatype contour
xyzlimits 555197 8573180 558849 8578566 0 1000
tolerances .5
margin 1
end
Arc: grid
Grid: fill dem fillfloat
Grid: filled = int (fillfloat * 100.0 + 0.5) /* integer centimeters
Grid: quit
Arc: gridimage filled # filled bil
The following two commands are calls to unix. Because there are large
flat spots, sloparea is called with an argument of 5000 instead of the
default 1000.
Arc: &sys sloparea filled 5000 Arc: &sys sed -e 's/NBITS 16/NBITS 32/' -e /ROWBYTES/d filled.hdr >! filledcum.hdr Arc: &sys cat filled.blw >! filledcum.blw Arc: imagegrid fillcmcum.bil flux Arc: grid Grid: tmpslopedeg = slope(dem) Grid: slopedeg = con(tmpslopedeg == 0,.01,tmpslopedeg)I do not use the "sloped" bil as I once did. Instead, I calculate slope from the original DEM, and then alter the zero values so that there will not be division by zero later. If I did want to use the sloped bil file, the vertical units are 1/5000 centimeters.
Grid: tanslope = tan(slopedeg div deg) Grid: sinslope = sin(slopedeg div deg) Grid: aobs = flux / sinslope Grid: &s T = 65 /* transmissivity Grid: &set depth 1 /* meter soil depth Grid: &s phi 33 /* angle of friction Grid: &s bd = 2.0 /* bulk density Grid: &set coh 2 /* kPascals Grid: &s tanphi [tan [angrad %phi%]] Grid: &s low = [calc [calc [calc %bd% - 1] / %bd%] * %tanphi%] Grid: wet1 = aobs / %T% / 1000 Grid: cossq = sqr(sinslope / tanslope) Grid: qsat = %T% * 1000 / aobs Grid: qnt%coh% = (1000 * %coh% / ( 9807 * %depth% * %tanphi% * cossq ) + %bd% * ( 1 - ( tanslope / %tanphi% )) ) * %T% * 1000 / aobs Grid: qust%coh% = con(tanslope < %low%,9999,qsat < qnt%coh%,10000,qnt%coh% < 0,0,qnt%coh% > 9000,9000,qnt%coh%) Grid: kill qnt%coh% all Grid: qust%coh%c = reclass (qust%coh%,/jo3/www/stability/unstord.reclass)
Download the American-made flux grid. This unzips to a directory named usa containing one grid. Zipped size is 26996379 bytes.