I've been working with SAGA GIS to calculate the Topographic Wetness Index of an alpine catchment. I am using the tool `Terrain analysis > Hydrology > SAGA Wetness Index` because, compared to `Terrain analysis > Hydrology > Topographic Wetness Index (TWI)`, the output is not a one-pixel wide film but a (to me) more realistic broader network of streams.

My input is a DEM (with sinks filled) that was derived from airborne LiDAR data and has a resolution of 1x1m. I don't have a *Weights* raster which is an optional input. Now my problem is that there are six parameters that shall be chosen before the calculation:

+ Suction (default = 10)
+ Type of Area (default = *square root of catchment area*; other options *total catchment area* or *specific catchment area*)
+ Type of Slope (default = *catchment slope*, other option *local slope*)
+ Minimum Slope (default = 0)
+ Offset Slope (default = 0.1)
+ Slope Weighting (default = 1)

Unfortunately, I didn't find much information about them and I am unsure how to decide which ones to use for my site. Both cited publications (Boehner et al 2002 and Boehner & Selige 2006) lack an explanation of these parameters and the SAGA tool itself has hardly any description (see http://www.saga-gis.org/saga_tool_doc/6.3.0/ta_hydrology_15.html). 

The latter, for example, says that for *Suction* "the lower this value is the stronger is the suction effect" but what is this suction effect and how strong should it be in my area?

References:

+ Boehner, J., Koethe, R. Conrad, O., Gross, J., Ringeler, A., Selige, T. (2002): Soil Regionalisation by Means of Terrain Analysis and Process Parameterisation. In: Micheli, E., Nachtergaele, F., Montanarella, L. [Ed.]: Soil Classification 2001. European Soil Bureau, Research Report No. 7, EUR 20398 EN, Luxembourg. pp.213-222. http://eusoils.jrc.ec.europa.eu/ESDB_Archive/eusoils_docs/esb_rr/EUR22646EN.pdf.
+ Boehner, J., Selige, T. (2006): Spatial prediction of soil attributes using terrain analysis and climate regionalisation. In: Boehner, J., McCloy, K.R., Strobl, J. [Eds.]: SAGA - Analysis and Modelling Applications, Goettinger Geographische Abhandlungen, Goettingen: 13-28. http://downloads.sourceforge.net/saga-gis/gga115_02.pdf.