Problem: SWAT creats too many HRUs

[Ren okumura]

Hi. I'd like to ask expert of SWAT. I have some problems.
The first problems is delete certain HRU. Some HRUs extend outside of land area. So, I'd like to delete choosen HRUs. Could you tell me how to delete HRU?

And, the other problem is that HRUs couldn't cover my target terrestrial area. Area where HRUs don't cover can't be calculated, right? So, I confsed because I want to calculate non-covered area. Therefore, could you tell me how to cover whole areas with HRUs?

Thanks.

[celray....@gmail.com]

I will rephrase to make sure I understand what you need:

"Firstly, I need to delete certain Hydrologic Response Units (HRUs) that extend outside of the land area (or my study area?). Could someone guide me on how to these HRUs?

Secondly, I'm struggling with HRUs that do not cover my entire target terrestrial area. Since areas not covered by HRUs cannot be calculated, I am uncertain about how to proceed. Could you advise me on how to ensure that the whole area is covered by HRUs so that I can perform the required calculations?"

If that is acurate,

1. You can restrict the area covered by delineation and hence HRUs by clipping your DEM to the desired study area. However, this is not recommended as the DEM is quite an accurate representation of the drainage system and clipping it may mean upstream channels are not included. If your study area is very flat, try using the burn in option.
2. If some area is not covered by HRUs, it could be that based on the topography, that area is outside the main watershed. You could add another outlet to the channel outlet from this area to have (two or more) independent catchments. This will make sure HRUs are created for that area.

All that said, it is hard to pinpoint what you are looking for without more context.

Cheers!

Celray James CHAWANDA

[Ren okumura]

Thanks for your response.

What you rephrase is collect.

As for the first question,  like this picture, HRU and subbasin area extend to sea area. 

So, the error that landuse/soil map don't cover with all HRU areas is sometimes occured. I consider it is derieved from these extended subbasin. That's why I'd like to delete this area. I already use burn-in stream(blu line) and outlet fanction.Do you know how to treat it?

The second question is non-HRUs covered area. My target is Ishigaki Island, Japan. After calculation by SWAT, I plan to use gwflow (similar with MODFLOW) for calculating growndwater schematic clearly. However,  non-covered area (example picture) doesn't have any stream. If non-coverd area aren't defined as land area, I won't be able to calculate these areas' groundwater system, right? I'd like to include these area as well because contribution of groundwater run-off is huge in these below area.

So, your reply is very useful for me. I'd like to ask you basic question. As you mentioned, what is independent catchment and how do I add the catchment?

2023年8月4日金曜日 11:55:20 UTC+9 celray....@gmail.com:

[celray....@gmail.com]

[Apologies if you receive this twice]

For the first one, I would clip the DEM along the shore line.

For the second one, please try reducing the Stream and Channel thresholds until you see channels in the 'non-HRU' area.

With Kind Regards,

Celray James CHAWANDA