r/Hydrology • u/Agreeable_Tomato_166 • 7d ago

How many subbasins are appropriate given the area and available fluviometric stations?

Hi everyone,
Apologies in advance if this is a basic question; I’m new to hydrological modeling and still learning the ropes.

I’m currently modeling a 2597 km² basin to generate a hydrograph at the location marked with pink dots and arrows in the image, using precipitation gauge data as input. (Note: The precipitation gauges are not shown in the image; only the streamflow stations are marked. The rainfall data I plan to use corresponds to a fast flood event.) I also have discharge data at the locations marked with red dots and arrows.

Initially, I planned to use only the discharge data from the outlet (final downstream station) to calibrate my model. However, I’m wondering if it’s possible—or advisable—to also incorporate data from the two upstream streamflow stations to improve the model.

Another question I have is about the number of subbasins. My model divides the basin into just five subbasins with two reaches (both reaches converge at the point where I want the hydrograph). Given the basin's size, does this level of simplification seem reasonable, or should I consider defining more subbasins to improve accuracy?

Thanks in advance.

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u/AwkwardlyPure 7d ago

It is in fact possible to do calibration by assigning weights to these gauges, this allows favouring the more important one for your application. I have done this in large scale applications. Your catchment area is relatively small I would say. Therefore, no need to subdivide if the outlet is your only interest. Reasons for subdividing is if the soil properties are very different within the project area, if you have rainfall gauge data at sufficient locations to better capture a spatiotemporal variability, and whether you indeed need the model results at intermediate locations. These are my few thoughts.

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u/Significant_Yam_3490 7d ago

Smart one here this

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u/OttoJohs 6d ago

I would break the subbasins up at the streamgage locations 🫠.

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u/Agreeable_Tomato_166 6d ago

You say I should calibrate the model for all three streamgages at the same time? Sorry if this is a basic question.

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u/OttoJohs 5d ago

Not a dumb question. I would calibrate the two upstream subbasins. Then use those values in the calibration for the downstream one.

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u/Agreeable_Tomato_166 5d ago

I will try to do that. Thanks for the answer :)