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I have a very detailed DEM of a region in Northern Germany. For hours I tried creating correct watersheds but my results all look illogical. Is it possible that bridges disturb the ArcMap Tools? I have a shapefile including the streams as vector lines but I don't know how to include them in one of the tools.

Here is one example cutout of my DEM, I marked the mentioned bridges (I'm not sure if "bridge" is the correct word to use: pipes which are covered by earth and allow ditches to flow underground).

enter image description here

My aim is to analyse the path which rains takes after hitting the ground, similar to the WMS service ofered by our local government (http://www.umweltkarten-niedersachsen.de/arcgis/services/Hydro_wms/MapServer/WMSServer?). An example from this WMS:

enter image description here

You can see that water from the green circuited area flows this way: "Hekelner Kanal" -> "Ollen West" -> "Motzener Kanal" -> "Weser" (which is subdivided into several sections).

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    The correct word is probably 'culvert'. It seems to me the answer is obviously yes it will effect your analysis because the watershed analysis tools will treat these as any other higher elevation land because it has no way of knowing they are culverts. – Alexander Dec 10 '15 at 10:30
  • Is there a standard procedure / tool available to clip a stream vector from a raster so that the culverts are eliminated? – Simon Dec 11 '15 at 9:02
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    Try 'burning' the streams in gis.stackexchange.com/a/18596/2856 – user2856 Dec 11 '15 at 11:20
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Yes it will mess things up completely but this is not an ArcGIS issue. How is ArcGIS supposed to know from a DEM that pipes run underground? Whitebox has developed a tool that will fix this issue and I demonstrate an ArcGIS solution at this location Account for bridge overpasses in a ground DEM to allow for water flow under the overpass.

Essentially the ArcGIS approach involves having a file of the underground "passes" and burning these into the DEM.

The Whitebox approach is called something like Breach Depressions and is outlined below and fully explained here.

The second approach is more inclusive and that is to apply the Breach Depressions tool to the DEM. The implementation of depression breaching in Whitebox uses a least-cost pathway approach to determining the breach path. This method is particularly well suited to reinforcing flow along roadside ditches and to identifying locations where culverts or bridges cut through road embankments (see illustration below). This can provide a much more suitable solution even when there are no ancillary data (e.g. a high quality road or stream network). It also will solve the common problem that road embankments cause when using depression filling to model surface flowpaths, i.e. the large artifact dams that often appear within river valleys behind embankments.

  • I already tried using the "Breach Depressions" tool in Whitebox and the "DEM Reconditioning" tool in ArcHydro (gis.stackexchange.com/questions/174044/…). Both tools lead to different results when creating the watersheds afterwards and I'm uncertain which one to trust. – Simon Jan 3 '16 at 10:49
  • I would fully expect them to be different, I would trust neither but research both. Whitebox provides you all the algorithms it uses for all operations (hence the name) and ArcHydro AGREE implementation is well cited as Hellweger, Ferdi, and David Maidment. "AGREE-DEM surface reconditioning system." Online at www. ce. utexas. edu/prof/maidment/gishydro/ferdi/research/agree/agree. html (last accessed March 3, 2005) (1997). You need to decide which one best suits your needs based on this information, the U Texas link will likley have changed since 2005. – If you do not know- just GIS Jan 3 '16 at 14:30

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