Erosion and drainage.

December 2010 Crops soils agronomy magazine reports on research concerning how subsurface hydrology affects soil erosion.  It appears to say that saturated soil erodes more easily than unsaturated soils.  This research confirms a practical idea that we have known for a long time.  Grassed waterways are constructed to protect the land from erosion.  In order for them to work properly, tile must be installed about 1/4 of the way across the waterway.  On the surface, it does  not make sense because it appears that water is running off too fast and needing to remove it from the subsoil should not be a problem.  However, in order to prevent erosion in the grassed waterway, saturation needs to be kept to a minimum.  I have advised many people who were repairing waterways that job would not be complete without tile.