When Loop Road regularly over-topped with water?
Over time the culverts that conveyed water under it clogged up and collapsed, causing water on the upstream side of the road to pile up (i.e. pool) on the upstream side of the road -- and overtop the road surface during peak water, especially after a big storm. Those events also caused the road surface to wash away, especially the fine material, leaving behind a loose assemblage of larger rocks. In spots, the road resembled a river bottom as a result.
New culverts were installed in 2008 in tandem with raising the road where it had washed out.
These days water flows under, not over, the limestone section of Loop Road.