ArcHydro Abflussabweichung

Question

<\/HEAD>Hallo!<\/P> Bei der Arbeit mit ArcHydro in ArcGIS 10 stimmen die Zusammenflüsse von Flussabschnitten (str, strlnk, drainage line) nicht genau mit den Einzugsgebietsgrenzen überein. Der Zusammenfluss liegt in allen Fällen 1\/2 Pixel flussabwärts von der Grenze entfernt. Siehe beigefügtes Bild.<\/P> Ich verwende ASTER GDEM. <\/P> Falls möglich, würde ich gerne erfahren, wie man diesen Fehler korrigieren kann.<\/P> Danke<\/P> <\/P> Gustavo Bonorino<\/P> Argentinien<\/P><\/BODY><\/HTML>

DavidBetts · Answer

Are the extra subbasins always at the lowest point of your analysis?

With the reply from Mark Boucher, I wonder if the "spurious subbasins" are just the product of GeoHMS needing to put the confluence in the next subbasin.

For these kinds of questions I've used TauDEM, so unfortunately I'm not familiar with the limitations and assumptions of GeoHMS.  No quick answers from me today.

MarkBoucher · Answer

I think what you see happening is normal. If you click on the pixels to see the flow accumulation value, you will see those at the bottom of the watershed (along the strlnk line and the last pixel before leaving the subbasin) are related to the area of the watershed (multiply fac by pixel area).  The confluence would NEED to be inside the next downstream catchment/subbasin/watershed.

I also agree that what we are dealing with is a digitized representation of something that is analog. So we have to except a more “grainy ” result in our analysis. Hydrology is a subset of the overall Civil Engineering discipline and C.E. can also stand for "close enough".

Mark Boucher, PE

Senior Hydrologist

Contra Costa County Flood Control

& Water Conservation District

GusBonorino · Answer

Hola David,

Cuyo, la tierra del sol y del vino.

Thanks for your message.

My concern is not with precision, however. When I go ahead with GeoHMS to construct the subbasins the misalignment resolves into spurious subbasins, as shown in the picture attached.

It must be something related to the configuration of ArcGIS or ArcHydro in my PC, but what?

All the best.

Gustavo

Gustavo González-Bonorino Centro Austral de Investigaciones Cientificas CADIC Av. Bernardo Houssay 200 Ushuaia, Tierra del Fuego (9410) Argentina

CedarCk_3.jpg