Or - and this was discussed at great length WAY back in one of the earlier threads - he simply stopped the car on the bridge with the road all clear, got out, went around the back, opened the tailgate, slid Allison out, (by dragging her, perhaps causing her jumper to ride up over her head), then just rolling her under the bridge railings. There's plenty of room under the bottom railing to roll a body.
Then slam the tailgate shut, get back in the car and shut the door (possibly the "couple of thuds" heard by locals) and drive off, doing a U-turn further up the road. That whole thing could have been done in 30 seconds or so, and any approaching vehicles would be seen and heard in plenty of time at night.
The body drops into the mud at about the high tide level, maybe bounces slightly with one end of it coming to rest under the bridge, and the rest poking out from under (which is where she was found).
And while the middle of the bridge may be about 14m high, I think where Allison was found would be less - may 8-10m. And if the tide was high, that mud would have been soft.
The subsequent heavy rain coincided with a LOW tide, and the hydrologist's report mentions that the highest level of the surge due to the rain didn't reach the level of the body - but the NORMAL high tide level DID. That's why the decomposition by water was so pronounced.
We have yet to hear about the tip of the rubber glove finger that fell out of the jumper sleeve - and whether or not this was from one of the Scene Of Crime people.
In fact, there is a LOT we have yet to hear. This was only day 1 - in a 4-week trial. We'll see just how close - or way off - our theories have been.