 Per the animated system map (see "External links"), Dardanelle Lock & Dam (lock 10), which forms Lake Dardanelle, is the highest facility on the system (54 feet between upper & lower pools); Ozark-Jeta Taylor Lock & Dam (lock 12), just above that lake, is the third highest (34 feet).Thus, it is likely that those two facilities were redesigned, in terms of height and possibly location, so as to eliminate lock 11 as originally planned.The Mississippi River lock is numbered lock 99 as it was added to the system after it was completed.