Drainage lines cross rivers

[Oystein_RussKristiansen]

I have ran ArcHydro (Arc Hydro Tools for ArcGIS 10.1 BETA) on a DEM (laser data, 10 "ground hits" per square meter and cell size 0,5):

Fil Sinks
Flow Direction
Flow Accumulation
Stream Definition
Stream Segmentation
Catchment Grid Delineation
Catchment Polygon Processing
Drainage Line Processing
Adjoint Catchment Processing
Drainage Point Processing

My problem is that the drainage lines a lot of times are crossing the rivers (se attachement). It seems to me that the drainage line, once meeting the river, should follow it and not crossing over, which it does all the time.

Apart from when the drainage lines are crossing the rivers, the analysis elsewhere is good.

Have any of you experienced this and could shed some light on have to solve this?

Best regards
Stein

[MarkBoucher]

Stein,

The graphical location of a stream will not always match the grid of the DEM. There are some "pre-fill sinks" steps that would fix this if you needed to. They are under the Terrain Processing>DEM Manipulation menu.

• DEM Reconditioning: In this step you choose a layer for the river (streams) and "burn" them into the DEM.


• Build Walls: In some cases the DEM is so flat it does not adequately define the terrain and will not give you the correct flow direction (the flow direction (fdr) grid is the basis of a good hydrologically correct DEM). You may not need to build walls in every situation. Just like the DEM Reconditioning burns stream (lowers the elevation of the DEM cells), the build walls function raises the elevation of the DEM cells.

The rivers in your attachment look like polygons. You would need to create a polyline equivalent and use that. You only need to add polylines for the river locations where the DEM is "confused" about where the stream/river is. After the streams/rivers are burned into the DEM, and therefore the DEM is lowered (could be as much as 1000 feet), the fill sinks function fills them back up to match the elevation of the downstream grid. After the fill sinks step, the river/stream is well defined in the DEM and your stream connections should look right. I always call the polyline layer agreestream since this is the Arc Hydro default and in most cases the Arc Hydro tools will automatically fill in that layer in the tools' dialogue boxes.

Hope this helps. See the link below my signature for a forum thread I established just for Arc Hydro problems solving.

[Oystein_RussKristiansen]

Hi Mark;

Thanks so much for your reply! I will follow your clues and see how it goes. I have a lot to learn in ArcGIS and ArcHydro, so your tips are very welcomed!

Best regards,
�?ystein