A Manual Method for Selecting Depression Contour Lines in ArcGIS

Currently in ArcGIS, there is no automated way for examining contour lines and selecting depression contour lines out of them. Depression or closed contours are used extensively in sinkholes studies and sinkholes can be considered as a subset of depression contours. Functions such as sink, fill, flow accumulation, flow direction under Hydrology tools (within Spatial Analyst extension) may look promising but they are more useful for sink or pit removal in digital elevation models (DEMs). The presence of sinks, which are spurious or irrelevant minima and not exactly sinkholes, may result in an erroneous flow direction raster during hydrologic modeling and landscape evolution studies and are removed to ensure the continuity of streamlines by raising elevations of a depression up to the lowest value among neighboring cells.

This study describes a manual method that can be used to evaluate contour lines and select those that are depression contour lines within ArcGIS platform. The method involves adding extra fields to the attribute table of the contour lines, using a layer symbology or color codes for contour lines that portrays progressive contour values, identifying depression contour based on repetition of colors, and assigning 1 to depression contours and 0 to rest of the contour lines in a specific field of the attribute table.

The objectives of this study were to - 1) find a quick, easy and simple method to select depression contours from a contour map produced from high resolution DEM, and 2) use the closed depressions for sinkhole study. The result from this study showed that this method was fast and easy depending on the contour interval and can be applied to larger areas.