Here is a link to the article where the police were searching Bunya St and Wirrabarra Rd.
http://www.news.com.au/national/pol...ents-in-the-area/story-e6frfkvr-1226345259099
Here is the link saying cars were seen at Anstead.
http://news.ninemsn.com.au/national/8468149/witness-comes-forward-in-baden-clay-case
If you Google Map Wirrabarra Rd, Anstead QLD, a map will come up showing Bunya, Wirrabarra, Mt Crosby Rd, Kholo Creek Crossing and Anstead.
(This is Kholo Creek Crossing - not Kholo Bridge, which is much further up river)
IMO Allison would have been left upstream and not at the bridge. It would be far too risky to throw anyone off the bridge, or even pull in to the siding and place a body under the bridge. If she was left near one of the dry creek beds, she may never have been found- if it had not rained. There is a lot of activity up Bunya St - Scout Camp, Laser Skirmish and houses - but Wirrabarra is far more isolated and hilly. And those dry creeks become torrents in heavy rain.
Canoeists wouldn't be up that far - not enough water- but they use the Brisbane River, or the mouth of Kholo Creek where it meets the river.
The swirling of water under the bridge pylons may have brought her to rest there - rather than her body be carried out into the river itself. Another poster explained this earlier. It is a miracle her body was found, IMO!
Hope this helps!