This is a very small and simple bridge designed to cross a pond in Japanese styled garden.
On a bridge of this scale I couldn't add handrails or really any details that you may get on a larger bridge.

I also won't go into too much detail because, with the possible exception of the beam bending, this is just as simple as it looks.

The cost of the timber was £20 and it took me about 3 afternoons to build and install.

Enjoy

Step 1: Materials

Design
The size and design of the bridge will have to fit the garden, this is a small garden so I made the bridge as slender as possible so as not to overpower its surroundings.

Materials
I used sawn treated pine, very rough cut pieces but they're cheap and treated to make them more durable.

- 19x32x2400mm, 8 pieces, these will form the curved beams, I only need 2 but it's good to have lots of spares

- 19x100x2400mm, 3 pieces, I sawed these planks in half to give me 50mm width planks, this was mainly to save money.
alternately just buy 19x50mm planks.

- Wood Glue, I recommend Evo Stick because the strength of the curved beams will depend a lot on the glue.

- Wood Screws, get exterior grade to ensure they don't rust away.

- Plastic Stakes, large plastic stakes to secure the bridge to the ground

Tools
This depends entirely on how good a finish you want to put on your bridge.

Basic Tools: Timber Saw, Drill, Mallet.

Finishing Tools: Plane, Power Sander / Sand Paper, Router.

Step 2: Laminating Beams

First you need to make the jig that will hold the beams as they set. Cut yourself a bunch of stakes from the smaller timber planks.

Using a mallet hammer these into the ground as shown so that you can hold your beams in a curve between them.

Each point uses two stakes. One straight down and one at a 45° angle to brace it.

Once you have set out your jig and tested it with a piece to see that you are happy with the curve you are ready to laminate.

Note: Pick your pieces carefully for this try to get a piece free of knots or weak spots, especially make sure there are no knots at the centre as this is where the greatest tension is placed during bending.

Place your first piece into the jig and then proceed to add a good layer of glue to your second piece. Starting at one of the ends, carefully align your second piece on top of the first and gently bend it round and secure it behind the stake at the other end.

Once the two pieces are glued and in the jig, make sure they are aligned and then add clamps in any places where the two aren't sitting directly next to each other.

Add screws along the length of the beam, every 200-300mm. make sure to drill pilot holes so you don't crack the wood.

Give the first beam about and hour for the glue to dry, then remove the clamps and you can repeat the process to create the second beam right on top, this ensures both beams have an identical curve.

I used a bin bag to ensure I didn't glue one beam to the other.

Leave the two beams for 24 hours to let the glue properly set, then you can remove both from the jig.

Step 3: Finishing Beams

Most of this step is optional, I used rough cuts of wood so I wanted to tidy them up a bit, you can buy pre-planed wood, but this is expensive.

I used a plane to even out the beams where they weren't properly aligned.

I then filled in any gaps and knots with wood filler.

After that I sanded the whole thing using 40 grit paper.

Step 4: Cutting and Finishing Planks

This step is pretty self explanatory.

First I planed and sanded the larger boards I bought.
Then I cut them in half lengthways to give me 50mm boards.
I cut these into 400mm lengths (the final width of my bridge) and then tidied them up a bit.

I also used a Dremel with a router attachment to add a 45° chamfered edge to all the boards to make them look a bit neater.

My bridge ended up needing 23 in all, always make a few extra in case you somehow mess one up.

Step 5: Completing the Frame

Again this step is pretty easy.

Mark and cut the ends of your curved beams so that they will sit flat on the ground.

Then screw two beams to some rough planks to make a square frame.

Each end plank has two holes drilled in it which will have plastic stakes pinning the whole frame down.

Step 6: Installation

Take your frame and set it down where you want to install your bridge. Take your time getting the placement right because it is a bit of a hassle to move it later.

I used 4 large plastic garden stakes to pin my frame in place.

Once this is done you can begin to put down your planks. Make sure the plank is centred and square with the rest of the frame, once the position is right drill through the plank and into the frame.

Once the two holes are drilled lift the plank back up, add a small amount of glue to where the plank meets the frame and screw the plank in place.

Continue to add planks in this fashion. I used two pencils to make sure that the gaps were even.

This process can be a bit tedious but once you get into a rhythm then you'll soon have it all screwed in place.

Note: you may find that the screws in the curved beams are in the way of where you want to place a plank, In this case you can remove the beam screws.
You must also be aware that towards the end of your bridge you may have to adjust your gap size to make sure that you don't have any frame peeking out.

Weatherproofing, I have left my timber bare, this way it will weather to a nice silver colour (it clashes a bit at the moment) you can wax or stain wood to protect it against the elements but I prefer not too.

Finished, you may notice a bit of bounce in the frame, but this should settle as the timber weathers. I'll try to update when the garden in finished and the bridge has weathered a bit.