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Strange contours in SCIMAP output

Sometimes the output from SCIMAP (SAGA GIS version) is not as expected and features strange contour line like features.


The image shows an incorrectly processed SCIMAP erosion risk map. The normal cause of this problem is when the height values in the DEM are all integers (i.e. no decimal places). This creates a landscape that is a series of terraces rather than a continuous surface. In your erosion risk map, the lines that look like contours are the steps between the different elevations values.

The normal cause of this problem is when the DEM is imported into ArcMap. The import dialogue has the option to import as either ‘integer’ or ‘float’ and frustratingly it defaults to ‘integer’. This is not great since you can go from float to integer without losing information but you cannot get back to float from integer since information is thrown away.


When you re-delimit the catchment, you may find that there are subtle differences in the catchment shape due to the greater information you have in these areas.