High value of sediment retention and sediment export

I want to ask about the output of the SDR. I have used the default parameter for threshold flow accumulation, sdrmax, kb and IC0 but the value were so high. Since the result were ton/pixel, so i converted to ton/hectare and the value were 1M++ ton/hectare. The value seems irrelevant because i have read a few article from my neighboring country, the value were not exceed to 100, 000 ton/hectare. Hence that, i wanted to ask if my data were relevant with the climate in my country (tropical climate).

Thank you.

Hi @Asyiqin, and welcome to the forum!

Model results are often much different than observed erosion, especially when we are using models that are very simplified, like InVEST is. There are several things you can think about when evaluating the results:

  • Always verify that your input data has the correct units. In this case, your Soil_K raster has values from 1 to 10, when the values should be much smaller, on the order of .01 - this is definitely contributing to large output values. You can look at the sample data provided with SDR to see an example.

  • Many times, most pixels have reasonable values, except for pixels with very steep slopes. Steep slopes are not represented well by the USLE equation, and often receive unrealistically high values of sediment export. We usually eliminate these values as outliers, but if they are a large proportion of your area, then this model might not be the best for your study.

  • It is always recommended to adjust the threshold flow accumulation value to match a real-world stream network. This often has a significant effect on the results.

  • If you have observed data, then it’s also suggested to do calibration of the model, so the model produces values that more closely match reality. With calibration, we’re often adjusting kb, IC0, etc.

You can find more information about these topics in the InVEST User Guide. Also, if you search this forum, you’ll find other discussions regarding high sediment export values that might be useful.

~ Stacie