We have a small stream in the back garden, which occasionally becomes a raging torrent taking water off the mountains behind us.
I needed to replace the rotten bridge and wanted to build an arched brick bridge. I've used engineering bricks - it's probably too red for this garden but the plants and moss will soften it over time. The bricks need to be tough and water resistant to cope with heavy water flow at times though.
The first job was to dig down to the water level and lay two concrete slabs as foundations for the brickwork. These slabs are probably bigger than they need to be but, again, always better to play safe and over compensate.
I then built a timber frame to support the brick archway and the concrete pathway in the centre - before covering with soil and laying grass seed.
There is about 7 inches of concrete in the path - laid in 3 layers with rebar and mesh added. I waited a month before removing the formwork.
.....and we put together a little video of the project too.