I used the SDR model on a watershed where I’ve sediment exportation value at the outlet of this watershed.
I can then calibrate the model based on the sediment exportation value.
I had to use a Borselli K Parameter equal to 8,7 to find a good match with actual results.
However, based on Hamel and al. (2015), Borselli K Parameter should have a value encompassed between 1 and 3.
I’m then wondering, according to your experience, can we use Borselli K Parameter value higher than 3 or lower than 1? If yes, what would be the maximum and the minimum?
Thanks in advance for you answer.
Hamel, P., Chaplin-Kramer, R., Sim, S., Mueller, C., 2015. A new approach to modeling the sediment retention service (InVEST 3.0): Case study of the Cape Fear catchment, North Carolina, USA. Science of the Total Environment 524–525 (2015) 166–177.
Thanks for your questions. When I need to calibrate SDR, I tend to stick with the guidance supplied by Hamel et al. 2015 for parameter ranges. I interpret reasonable ranges as follows (see Figures 2 and 5):
IC0: 0.1 - 0.8
kb: 0.5 - 3.0
SDRmax: 0.0 - 0.8 .
So, kb can be lower than 1.0, but I would not recommend exceeding 3.0.
Are you using an InVEST version ≥3.14.0? How did you obtain the sediment export value at the watershed outlet and is that an annual value?
I use InVEST 3.14.
I’ve got annual sediment export value at the watershed outlet from a publication which used several water quality stations data and estimated (modeled) annual sediment export. But I guess these values take in account all possible erosion process (for ex. streambank erosion, gully) while SDR model only focus on overland erosion.
Do you then know if there is a general proportion associated with each erosion process ? (for ex. 20% associated streambank, 10% associated with gullies, 70% associated with overland erosion).
I guess not since it is probably widely variable from a watershed to another according to topography, intensity and duration of rainfall, soil erodibility.
No, there is certainly no general proportion to associate with sources of sediment. This is exactly for the reason for describe, that watersheds around the world are highly variable especially in terms of soil type, slope, climate, and vegetative cover (both type and quality).
To get at this for your region of interest, it’s important to find studies or reports that characterize your watersheds. Of note, another potentially major source of sediment loads that you didn’t mention, but which the InVEST SDR model also does NOT consider, is mass wasting (e.g.: landslides).
You also should be aware of, and account for, whether of not the streams and rivers are free-flowing or if they are impacted by built entrapments, like dams or levees.
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