Pooh sticks bridge (originally known as Posingford bridge) was built in 1907. After making the model I was surprised to find another photo of a different design. Instead of two posts in-between each span there was only one. It turns out the bridge has been reconstructed twice, once in 1979 and the other in 1999. The design I worked from was the 1907-1979 and 1999-current.
The Meccano bridge is not quite to scale. It should be slightly wider and the railings should not be so high. However this is difficult with the ½" Meccano hole spacing. All other limitations are due to lack of parts. Narrow strips would have looked a lot better for a lot of the railings. The bridge legs are also missing the internal support. Another aspect which is a bit disappointing is the decking made of 5½" x 2½" plates instead of 5½" perforated strips.
The river section is made out of blue plastic plates and cams give enough vibration to move the Pooh sticks down the 'river'. Fork pieces are used as Pooh sticks because they do not roll.
In July 2010 I managed to build the bridge as I originally wanted. Please see the extra photos.