Preserve the trail surface, okay. In many of the images I see from the C&O, clearance between the canal and the trail surface for a tow rope is not maintained. Their definition of "canal operation" seems arbitrary.
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A serious twisting of what I said, and what their guidelines are. I simply stated their rule regarding the composition of soil used, stating correctly that it is to be the same composition as what was there when the towpath was operational. Nothing was stated that could possibly construed as needing to keep it operational in regard to clearance for a tow rope. That is absurd, they are not keeping the canal operational. All that was stated was that the soil composition on the path be the same as it was when the canal was operational. This was from park service employees in 2011. I do not knwo if their regulations have changed, but I sincerely doubt it.
All that being said, I am still amazed when I hear people telling horror stories of the path when wet. I did it during a hurricane that was hitting DC. As a result, we had torrential downpours while on the trail. I used Continental City Contacts for the ride and had zero issues. The surface gave decent traction despite being soaked, and having standing water. Many of the horror stories came from people riding with no fenders. I believe a lot of the negativity is a perception based on the mess and aggravation caused by the lack of fenders. When one is wet and muddy, your perception will never be positive, unless that is your type of thing.
I still tend to prefer the C&O over the GAP, which is the trail I ride frequently. I wish the C&O were closer so I could ride it more.