Garden arched bridge
I eventually finished the garden bridge.
I think it has taken about the same amount of time to work out how to send a photo by email, so trust that it gets to you OK.
The span of the bridge is about 3.6 meters. I used the same size battens as per your plan, as I thought the thicker ones might be a bit hard to bend. Using six instead of four, and expanding the scale appropriately, I achieved about the same curvature as in your plans. I added an extra stauchion to keep appropriate proportions, and made the walkway a little wider (80 cms) so that I can get a wheelbarrow across to the island.
For glue I used Fullers Max Bond, as the epoxy resins available here would have almost doubled the cost of materials. I used treated pine screws for fasteners , and gave the finished structure a couple of coats of Cabot's Decking Oil. The bridge sits on a footplate of H4 treated pine at each end, which keeps the H3 timber out of contact with the soil. Total cost was approximately A$250, which compared more than favorably with the $1750 I was quoted to have one built - and that didn't have a properly constructed arch, but rather just a curved shape that was cut out of a slab.
Click on image to enlarge.