Eliminating Subcatchment Polygons

[BrianPenserini]

I have a feature class that contains polygons representing catchments derived from using the Adjoint Catchment Processing tool in Arc Hydro Tools. To the best of my knowledge, this feature class 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). I have eliminated all polygons with areas above an upper area limit as well as polygons below a lower area limit by using "Select by Attributes" in the attribute table of the feature class and deleting the selected features, but I am still left with polygons that are overlapped by larger polygons (essentially the subcatchments within a larger catchment). I would like to eliminate all of the polygons that are subcatchments and contain areas that are contained within a larger polygon in the same feature class, but all of the tools I have tried so far do not produce my desired result. Any help would be greatly appreciated. Arc Hydro​​

[MarkBoucher]

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

[MarkBoucher]

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.