Poorly functioning grassed waterway. A grassed waterway is a broad, shallow channel designed to move surface water across farmland without causing erosion. If not maintained properly, they can fill with sediment causing water to flow along the edge, resulting in ephemeral gully erosion. Ephemeral gully erosion is one of the main mechanisms for off-site delivery of sediment and attached nutrients in surface runoff. Image courtesy of Kevin Kuehner, Minnesota Department of Agriculture.