Eliminace polygonů Subcatchment

Question

<\/HEAD>Mám třídu prvků, která obsahuje polygony představující povodí odvozená pomocí nástroje Adjoint Catchment Processing v Arc Hydro Tools. Podle mých nejlepších znalostí tato třída prvků obsahuje polygony všech povodí z mého DEM nad určitou prahovou hodnotou odtokové plochy, včetně povodí, která jsou vnořena do většího povodí (subcatchments). Eliminoval jsem všechny polygony s plochami nad horním limitem plochy i polygony pod dolním limitem plochy pomocí "Select by Attributes" v tabulce atributů třídy prvků a odstraněním vybraných prvků, ale stále mi zůstávají polygony, které jsou překryty většími polygony (v podstatě subcatchments uvnitř většího povodí). Chtěl bych eliminovat všechny polygony, které jsou subcatchments a obsahují plochy, jež jsou obsaženy ve větším polygonu ve stejné třídě prvků, ale všechny nástroje, které jsem zatím vyzkoušel, nedávají požadovaný výsledek. Jakákoli pomoc by byla velmi oceněna. Arc Hydro<\/A><\/P><\/BODY><\/HTML>

MarkBoucher · Answer

Brian, In response to:

"To the best of my knowledge, this feature class [AdjointCatchment] contains polygons of all of the catchments from my DEM above a certain threshold drainage area, including the catchments that are nested within a larger catchment (subcatchments)."

Lets say you wanted to delineate a watershed that did not coincide with a DrainagePoint. Delineating only using the flow direction grid (fdr) is very slow. If we calculate the Catchments at the DrainagePoints, some of that work is already done.

The AdjointCatchment (ACat for short) is precisely created to overlap the Catchment polygons and allow us to capitalize on the Catchment polys by conglomerating (adjoining) them. Then to delineate any point, one must only delineate a small portion downstream of a DrainagePoint using the fdr grid and then use the ACat polys to immediately define the rest of the delineation.

MarkBoucher · Answer

The appropriate way to use our Arc Hydro is to develop the Catchments and AdjointCatchments first and leave them alone. The Catchments  and AdjointCatchments are used by Arc Hydro in performing the delineation by "Batch_Points".  Their whole purpose is to speed up the delineation process.

You place "Batch_Points" at the locations where you want to calculate flows. You can use the drainage points created by Arc Hydro (Copy or snap to while creating. The Batch_Point feature table has specific fields. Create at least one point using the Batch Point creation tool, then copy other points to that dataset). Then use the Arc Hydro Watershed Processing tool Batch Subwatershed Delineation to delineate the Subwatersheds you want for your study based on the Batch_Points locations. GeoHMS has a tool that "imports" Batch_Points. I use this all the time without having to use other GeoHMS functions.

In Arc Hydro, Subwatersheds do not overlap and Watersheds do overlap. So, pick which you want. You can create both. They are created in different datasets. To use the batch points again, you have to calculate the BatchDone field to zero.

I'm doing this from home and don't have access to the software to make sure all of my terms are correct. I may look at this tomorrow and double check that I'm communicating correctly. I have updated this reply considerably after getting into the office this AM.

Mark Boucher