I have a small ditch that I dug to route some water. It turns out that it does not work, so I was wanting to fill it back in. The ditch is about a foot deep in some places. Can I compact new topsoil with a large block of wood and a sledge hammer?
If your available tools include a sledgehammer, just use that, held vertically, head down, pick it up and drop it, repeatedly, every 2 or 3 inches of soil fill (you cannot effectively tamp thicker layers of soil with hand tools.)
Forget the wood block.