The drain in my garden or yard is overflowing. What’s happening?

Outside drains block more often than internal ones, because they collect a wider range of debris: leaves, silt, paper, twigs and plastics that wash in from open ground. A gully (the grated drain at ground level) can clog at the grate or in the trap below it.

If an outside drain is overflowing:

Clear any visible debris from the grate.
Check the gully trap beneath for trapped silt and waste.
If the chamber is full and not draining, the blockage is downstream in the main drain.

A full inspection chamber or an overflowing manhole points to a blockage in the main run. This usually needs jetting or rodding by an engineer, and acting quickly matters because a backed-up main drain affects the whole property.