Gullies

A gully is a landform created by erosion, typically involving most discharge of runoff that cuts a channel through soil or rock. Gullies form when water runs off a surface and gathers in a confined space, concentrating energy that dislodges sediment. They commonly develop on slopes, in agricultural fields, or in urban drainage areas where surface runoff is increased by impervious surfaces.

The initiation of a gully usually begins with a small depression or rill. Repeated wetting and drying cycles cause material to loosen, and if stormwater continues to flow, the depression expands into a deeper channel. Over time, sediment removal by gravity and water flow deepens and widens the gully. The final size depends on slope gradient, soil type, vegetation cover, rainfall intensity, and existing drainage infrastructure.

There are several types of gullies. Classical open channels are found on hillslopes and can be permanent or seasonal depending on aridity. Ephemeral gullies form only during heavy rains and may appear as bare scars. Subsurface gullies occur where dissolution or detachment of soil happens below ground, often in clay-rich soils. Urban gullies, often termed “stream gills,” are artificial channels created by storm drains and can quickly become buried or blocked.

Gullies can pose environmental and safety risks. They contribute to soil erosion, reduce agricultural productivity, and transport pollutants into watercourses. In urban areas, gullies can become overflow points during storms, leading to flooding. Mitigation measures include re-vegetation, installing check dams, constructing drainage infrastructure, and controlling land use changes on steep slopes. Restoration of gullied areas usually involves soil stabilization, erosion control blankets, and sometimes engineered small channels to redirect surface flow.

Because gullies are dynamic features of the landscape, ongoing monitoring is important. Their growth can be modeled using hydrologic and geomorphic data, allowing planners to predict future paths and to design appropriate countermeasures. Accurate identification and assessment of gullies help reduce erosion, protect water quality, and safeguard human settlements situated near vulnerable slopes.