Another visit to sump 12. Previously, after various digging trips, an underwater connection was made between sump 12 and sump 12a. At the weekend we went back with the intention of following the main flow of the water between sumps 12 and 12a. From sump 12a, 25m of line was laid to a depth of 13.1m. It was at this point we were met with a gravel bank wall with the full flow of the water just filtering through gravel. No possible way on was noted unless the gravel was dug out. This now explains why sump 12 backs up so high in flood. Although this gravel bank (similar to that at the end of Wookey Hole) could be dug, the spoil would have to be transported back to the surface in sump 12a and then back to sump 12 by either the underwater route or the dry route.