gully

A gully is a narrow, steep-sided channel formed by the concentrated flow of water in soil or weak rock. It is larger than a rill and can deepen into a ravine with continued erosion.

Gully formation starts when runoff concentrates on a slope, initiating erosion that enlarges small channels. Headward erosion at the gully head can advance upslope. Factors include rainfall intensity, slope, soil texture, vegetation cover, and land use. Gullies may be seasonal or persistent, appearing in a range of climates from arid to humid tropical regions.

Typical features include a defined channel, cut banks, and a gully head from which erosion propagates. Cross sections vary from V-shaped in bedrock to broad, flat-bottomed in loose sediments. Gullies differ from ravines and canyons mainly in scale and persistence.

Environmental and economic impacts include loss of fertile soil, reduced agricultural productivity, and increased sediment yield to streams. Management approaches emphasize stabilizing the head, restoring vegetation, improving drainage, and building structures such as check dams or gully plugs to slow erosion and promote sediment deposition.

The term also appears in place names and as a surname. In everyday use, gully can refer to a drainage ditch or natural channel formed by erosive runoff.