Questions on impact of channel delineation on LSUs and using LSU shapefile

[Fereshteh Kordrostami]

Hello everyone,

I have two questions:

1. Channel delineation thresholds:
If lower drainage-area thresholds are used during watershed delineation to create a denser stream/channel network, does this directly lead to an increase in the number of landscape units (LSUs), or are LSUs largely independent of channel network density?

2. Using LSU.shp as an alternative to hru2.shp:
When using the dominant HRU option (1 HRU per LSU) to filter the HRUs from hru1.shp, is it conceptually and technically acceptable to use the final LSU.shp as a spatial alternative to the created hru2.shp to solve the issue of existing holes of filtered HRUs in it?

I would appreciate any answers or insights on these points.  

Thanks,
Fereshteh

[Chris George]

1. There is one LSU (or a pair if you define floodplains) per channel
reach. So if the lower threshold produces more channel reaches there
will be more LSUs.

2. You are right to think that a single HRU per LSU will avoid the
problem of holes in the hru2 shapefile. Another approach would be to
define a zero minimum HRU area when filtering by area, or to use the
maximum number in filtering by the number of HRUs: either of these will
preserve all HRUs. Another possibility might be to do your intersection
with other data on the hru1 file and extend your results to the selected
HRUs: it depends on what you are trying to achieve.

Chris

On 1/28/2026 12:38 AM, Fereshteh Kordrostami wrote:
> Hello everyone, I have two questions: 1. Channel delineation thresholds:
> If lower drainage-area thresholds are used during watershed delineation
> to create a denser stream/channel network, does this directly lead to an
> increase in the number

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[Fereshteh Kordrostami]

Thanks for the suggestions. 

My goal is that my initial generated HRU map resulted in 64,000 HRUs. I am hoping to reduce the total count to improve the runtime speed, but when I run the tool to generate an HRU2 file, but that contains substantial gaps in the watershed. I've tried each option, but each yields the large gaps (see attached images). 

I was told previously the gaps are merged into the reduced HRU2 shp file, but there is no way to find what gap is associated with the new HRUs. Is there a SWAT output file (database or textinout) or means to get from QSWAT, a map that connects the HRU1 to the HRU2 shp file. This is necessary for post-processing to produce images that include the results within the area gaps. I saw in the qswatplus-tutorial.pdf file a reference to an output file called HruLanduseSoilSlopeRepSwat.txt (Fig. 23), but was unable to find it after running the program.

A separate question is that when I filter the HRUs by the dominant HRU option, it does not include the exempting landuse option (LU to always be in use). Is there a way to enable this feature?

Thanks

Fereshteh 

[Chris George]

The gaps in the hru2 shapefile are the HRUs removed by whatever filter
method you used. These gaps are imaginary: in the model the remaining
HRUs are expanded in area to fill the model. There is no way I know of
of illustrating this in a map. If you want to not have any gaps in the
hru2 file then don't filter any HRUs, eg by setting the area threshold
to zero.

The hru2 shapefile is just the hru1 shapefile with shapes for the
filtered HRUs removed.

The textual HRU output file is in the Watershed/Text directory of the
project.

If you want to choose the dominant HRU then you get the dominant HRU's
landuse, of course. If you want to make a model with every subbasin
having one HRU with the same landuse then make this landuse exempt from
elimination and filter HRUs by using the number of HRUs option and set
the number to the number of subbasins.

Chris

On 2/3/2026 8:08 PM, Fereshteh Kordrostami wrote:
> Thanks for the suggestions. My goal is that my initial generated HRU map
> resulted in 64,000 HRUs. I am hoping to reduce the total count to
> improve the runtime speed, but when I run the tool to generate an HRU2
> file, but that contains substantial

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