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.