I camped there a week ago fella's. At the moment (& it may have been low water level in the middle of the year) the water level is roughly 800 - 1.2m all the way accross. The middle is also very sandy & squelches between your toes when walking. Additionally the water was flowing at between 7 - 10knots (very fast). Remember that with water up near the top of the tyres (about 750mm) it will only take a car length of deeper water (or a softer bottom) to create a floating boat (as your doors are sealed).
We heard the day before we got there that someone had tried in their brand new Navara & had rigged up 75m of Dynema rope + 8 snatch straps that reached to the other side & off he set. Halfway accross he was floating then he opened the door to get out! Bad move as the car then filled with water & the rope broke (even Dynema can't hold back the river). Sure enough on my way out two days later there was the Navara snagged in the trees about 3 kms down stream upside down.
Also releasize that the level of the Jardine doesn't always follow the patterns of rain, ie you can have a small wet but still get huge amounts of water coming down. This is because more than 50% of the water (in all of the creeks up there) comes from an underground aquifer from PNG.
Nolan's Brook last week was also about 1 - 1.2 meters in the centre as was Cannibal Creek (the ruts on the northern bank also make Cannibal "winch out only country"). The other VERY bad one was the southern bank at Palm Creek - it's ok gowing north but winch out only coming south. Gunshot was a doddle - but I did take the chicken track!
About the permits & fines. I've never heard of anyone getting fined for using the old Jardine Crossing. I have also done a one way trip (coming down from North after loading my 4x4 onto the freighter in Cairns & getting it offloaded at Seisia/Bamaga) & back over the Jardine ferry where I wasn't even asked to produce a ticket (the ferry guy just assumes that everybody has come up beforehand so doesn't ask).
My recommendation regarding the old Jardine crossing is - if it has more than 750mm of water in it anywhere accross the entire width AND/OR it is flowing at more than 5 knots - then don't try. Unless of course you are prepared to throw your car away. Good luck.