Gary, Scott and I jumped right in to Steamboat when they needed a re-build at no cost. The bros up there were good enough to give us a couple of dry tops but we re-built the D-hole when it needed to be done at no cost.
Whitewater Parks vary greatly in their ability to hold up over time. The number one factor is the quality of the bed material. If a river is naturally armored, i.e. large cobble and no historic impacts like dredging (Blue in Breck), then they usually hold up well. Sediment deposition and scouring are the number one reason you will see change in a feature year to year. There is not much to be done about that issue. Hopefully most drops scour and deposit in a manner that closely approximates a river's natural cycle, but digging out eddys every few years is an exercise in futility.
Every whitewater park in the State is owned by a city or some municipality and the normal types of maintenance required is the responsibility of the local government. However I know here in Salida I always have to bring things to the City's attention and often have to raise money to make things happen. For example the new hole at the Boatramp was entirely built with money we raised over the winter.
We always tell communities that they will need to maintain the parks but honestly most of the maintence falls under normal park maintenece type of issues. Cities already know this because every recreational ammenity that a community builds requires some level of up-keep.
If you want to e-mail me with the specific issues you are seeing and in which park maybe I can give you a hand. email@example.com