For what it's worth, the southern most part is never going to be a suitable bike trail.
Those trails were still fine and rideable prior to the logging damage. What the tornado destroyed could be fixed, what the loggers destroyed is gone forever. Back in the day, the southern part always flooded at the slough but now the entire trail is useless until summer. We cut a switch back to connect the loop because the slough was always impassable. I've been back in there for 20 years, why they followed the log trails for hiking or biking is just stupid.
I'm not sure how you can condition a trail for biking or hiking that has 12" deep ruts and is 7' wide.
For the most part, the loop, which consists of the trails just north and south of the levee trail usually stay dry enough even in the heaviest rains.
http://southernindianamtb.ning.com/