GJ, hope you got out to Hinze and Nerang to check things out since your OP. For those who don't know, the Hinze Dam originally had a track used for Gold Coast MTB Club races. It was lost with the dam expansion. Peter Hallinan from the club has fought to have that lost trail re-built. Weather on the Gold Coast during reconstruction was dreadful. Massive rains and storm damage came during and just after construction, when trail was very vulnerable.
Almost all trail can be made weather proof to an extent, but it depends on circumstance and relies on support from volunteers to keep trails going. Rain doesn't just damage trail, it encourages aggressive regrowth of vegetation. When seepage is discussed at Hinze, you can bet it is not coming from the dam, because they check it continuously and there is a water flow monitor right next to part of the MTB trail. The wettest area is down lower, near the creek crossing. I would guess that area is now dry like Nerang. We have watched the wattle flower from top to bottom as the subsoil water soaked away this Winter and Spring and now all is dry on the GC.
Anyway, the club social rides are still on every Saturday arvo from Just Ride bike shop at 2.30 and 2.45 for aerobic and funrobic groups. If making trails awesome is something you desire, then check here
http://www.mtbtrailcare.com/Calendar.asp
and here
http://www.mtbtrailcare.com/Default.asp