Is it possible to account for unclean benches in RocFall?

There are a couple of methods that can be used to account for unclean benches.

First, alter the coefficient of restitution values to model the loss in bounce height due to debris.  Secondly, change the slope roughness for the material to account for debris.  

Both of these parameters are defined in the Material Editor (Slope menu).  In both cases, you have to back-analyze field data to get the parameters right.