In the 20 odd years that I lived on the Eungella Range I have had to drive through water on either side of this rise. Often using the white line as a guide.
While I have never found it to be an island many of my friends have. Water is known to sit on both side of this rise. Hard to believe. Sometimes its flooding on one side but not the other, Often a raging torrent too, I've seen that many, many times. The water tends to go down quickly enought to traverse through but the wait can be a couple of hours if your unlucky enought to get caught between the flooded areas.
When travelling through flood ways try to give way to vechicals already in the water. The best and shallowest place is usually the middle of the road (hense following the white line). Don't drive with undue speed it will cause problems with flooding your car/engine and even others. Try to access the water before you enter it. It won't be the same depth all the way through. Be courteous.
If you have any doubts wait till the levels reciede. I know heaps of people who have been gungho and ended up sorry. Flash flooding will happen quickly. Dont be caught out.