Drainage trenches are usually about 12 inches wide and 18 to 24 inches deep. Most drains use a 4-inch meter pipe. In other words, a 12-inch-wide-trench leaves you room for gravel and fill. A minimum 18-inch depth allows room for a gravel bed, piping, rock gravel, and topsoil if you choose.

Because there is a direct relationship between the diameter of a drain pipe and its relative effectiveness, your trench should be at least 12 inches wide. Aim for a depth between 18 and 24 inches.

The trench should be at least 18 inches deep to accommodate the gravel base and pipe. If you’re including a dry well, dig a hole bigger than the dry well where the water congregates. While all you need is a shovel and a will to work, there are a few tools that can help make trench digging easier: Trench shovel or drain spade.

You may aim for a depth of two feet if you want the drain to be more reliable. The deeper a drain, the more resistant it is to damage caused by weather and external factors. If you have a scenario where the house is pretty much in a low lying area then you have to dig a deeper trench.