Hi.
Has anyone here used the latest version of SDR that needs LMax for calibration?
Would i like to know how you chose the L max value to calibrate?
Did you choose the Lmax value based on the Lmed and the average slope?
I have not found publications that have exposed this procedure. If you can direct me.
I’m Brazilian and my English is not very good, so I’m sorry for any mistake.
Hi @BiancaBendito ,
Thanks for writing in with this question.
If you’re like me in that you do not have any specialized knowledge of the Lmax parameter, we recommend using the default value of 122. The literature that describes the method to calculate the LS factor for a two-dimensional surface is older and was developed by Desmet and Govers (1996):
Desmet, P. J. J., and Gerard Govers. A GIS procedure for automatically calculating the USLE LS factor on topographically complex landscape units." Journal of soil and water conservation 51.5 (1996): 427-433.
As the InVEST User Guide states, “To avoid overestimation of the LS factor in heterogeneous landscapes, long slope lengths are capped to a maximum value of 122m that is adjustable as a user parameter (Desmet and Govers, 1996; Renard et al., 1997).”
Here is the second full citation: Renard, K. G., Foster, G. R., Weesies, G. A., McCool, D. K., & Yoder, D. C. “Predicting soil erosion by water: A guide to conservation planning with the Revised Universal Soil Loss Equation (RUSLE).” Agriculture handbook 703 (1996): 25-28.
Please reference the User Guide for more details, specifically the “Annual Soil Loss” section that I linked above. I’m sorry that I do not have a deeper understanding, but hopefully this information is helpful to you.
-Jesse
Hi Jesse thanks for the feedback.
I think the value of 122 is too high for my area of study in Brazil.
The average slope of the hydrographic basin that I am studying is 15% and the Lmed is 0.40800. The drainage density is 1.23.
So I believe that an Lmax of 122 is very large and this will generate a much higher sediment export than the output of the basin.
My advisor suggested 4 for LMax, but I still don’t know where he got that value.
I didn’t find the “Annual Soil Loss” section in the guide.
I looked at the latest version of the gui and I didn’t find it. Can you help me?
Hi @BiancaBendito,
A value of 4 sounds quite low to me. I’m pinging our Senior Hydrologist @RafaSchmitt here to solicit his help since he has thought a lot about this parameter lately.
The link from my previous post should take you directly to the “Annual Soil Loss” section in the SDR chapter of the User Guide. If not, try this link. I also included a screenshot of the section below.
-Jesse
