How To Build A Sleeper Wall. Retaining walls are never cheap or easy but building one from timber railway sleepers is probably as cheap and easy as you are likely to find. For example if it's along the edge of a path how wide does the path need to be?
If there's going to be water building up behind the wall, where will it go?
Let me mention @adam_w so they are alerted to your kind feedback. Space the supports every 1.2m for 2.4m long sleepers, and water can build up significant pressure behind a retaining wall so it's important you provide for drainage behind it. Before starting to dig, use spray paint to outline the water feature's wall and basin on the ground. Installing the wall is labor if the hill is taller than 4 feet, plan to build multiple retaining walls up the hill to create a tiered look.