Two months ago I decided to reconfigure my ditch. Yesterday we received about 3" of rain in 1.5 hours and this morning, I noticed the ground sinking pretty bad where I had backfilled the ditch. What can I do to fix the problem? I used river sand as backfill, and it was compacted and flooded before planting the sod. The sod had been growing for about 4 weeks now. I used an earthen fabric that goes along the bottom of the ditch and wraps up just past the seam of the 2x8 and 2x10.