Gully

The earliest known usage of the term is from 1657. It originates from the French word goulet, a diminutive form of goule which means throat. It is possible that the term is connected to the name of a type of knife used at the time, a gully-knife.

Water erosion is more likely to occur on steep terrain because of erosive pressures, splashes, scour, and transport. Slope characteristics, such as slope length and amounts proportionate to slope length, affect soil erosion. Relief and soil erosion are positively correlated in southeast Nigeria.[3] There are three types of topography: mountains, cuesta landscapes, and plains and lowlands. While highlands with stable lithology avoid gullying yet allow for vigorous runoff, uplands with friable sandstones are more prone to erosion.

Gully erosion can progress through a variety and combination of processes. The erosion processes include incision and bank erosion by water flow, mass movement of saturated or unsaturated bank or wall material, groundwater seepage - sapping the overlying material, collapse of soil pipes or tunnels in dispersive soils, or a combination of these to a greater or lesser degree. Hillsides are more prone to gully erosion when they are cleared of vegetation cover, through deforestation, over-grazing or other means. Gullies in rangelands can be initiated by concentrated water flow down tracks worn by livestock or vehicle tracks. The eroded soil is easily carried by the flowing water after being dislodged from the ground, normally when rainfall falls during short, intense storms such as during thunderstorms.

A gully may grow in length by means of headward (i.e. upstream) erosion at a knick point. This erosion can result from interflow and soil piping (internal erosion) as well as surface runoff. Gully erosion may also advance laterally by similar methods, including mass movement, acting on the gully walls (banks) and by developing 'branches' (a type of tributary).

Gullies reduce the productivity of farmlands where they incise into the land, and produce sediment that may choke downstream waterbodies, and reduce water quality within the drainage system and lake or coastal system. Because of this, much effort is investeinto the study of gullies within the scope of geomorphology and soil science, in the prevention of gully erosion, andthe in remediation and rehabilitation of gullied landscapes. The total soil loss from gully formation and subsequent downstream river sedimentation can be substantial, especially from unstable soil materials prone to dispersion.

When water is directed over exposed ground, gully erosion happens, removing soil near drainage lines. This may result in issues like divided properties, loss of arable land, diminished amenities, and decreased property values. Additionally, it can lead to sedimentation, discoloration of the water supply, and the creation of a haven for rodents.[4]

Water rushing over exposed, naked soil creates gullies and ridges that erode rock and soil. When water rushes across exposed terrain, it erodes or pushes dirt away, creating rills. Gravity causes rift erosion to occur on a downward slope, with steeper slopes generating greater water flow. Sandier terrains are more commonly affected by rills, which are most prevalent during the rainier months. Gullies develop when a rill is neglected for an extended period of time, thickening and expanding as soil erosion persists.[5]

The factors influencing gully erosion were investigated in Zaria, Kaduna state, Nigeria, utilizing SRTM imagery, soil samples, rainfall data, and satellite imagery. The findings indicated that the factors that had the biggest effects on gully erosion were slope (56%) and rainfall (26%), land cover (12%), and soil (6%). The investigation came to the conclusion that soil loss was significantly influenced by a particular component.[6]

Effects of Gully

The effect of gully in an environment cannot be overemphasized. The loss of fertile farmland due to gully erosion is a serious environmental problem that lowers crop quality and may cause famine and food shortages. It also causes the soil to lose organic content, which has an impact on plant viability. As items washed from fields end up in rivers, streams, or vacant land, erosion also contaminates the ecosystem. Because of increased population expansion and increasing land demand, erosion is also a threat to the natural ecosystem, encroaching on natural forests. Important assets including homes, power poles, and water pipelines are also destroyed.[7]

Gullies can be formed or enlarged by a number of human activities.

Artificial gullies are formed during hydraulic mining when jets or streams of water are projected onto soft alluvial deposits to extract gold or tin ore. The remains of such mining methods are very visible landform features in old goldfields such as in California and northern Spain. The badlands at Las Medulas for example, were created during the Roman period by hushing or hydraulic mining of the gold-rich alluvium with water supplied by numerous aqueducts tapping nearby rivers.[16] Each aqueduct produced large gullies below by erosion of the soft deposits. The effluvium was carefully washed with smaller streams of water to extract the nuggets and gold dust.

A research presents RF-ADTree, a hybrid artificial intelligence approach that uses alternating decision trees (ADTree) as the basis classifier and rotation forest (RF) as a meta/ensemble classifier. It forecasts gully erosion in Iran's Kurdistan province's Klocheh watershed. 22 conditioning factors and 915 gully erosion areas are used in the model. According to the results, there are 19 characteristics that are useful for modeling gullies, and the RF-ADTree ensemble model considerably increases prediction accuracy.[17]

Gully initiation is the result of localized erosion by surface runoff, often focusing on areas where forest cover has been removed for agricultural purposes, uneven compaction of surface soils by foot and wheeled traffic, and poorly designed road culverts and gutters.[18] Termination of gully processes requires water-resource management, soil conservation, and community migration. Gully erosion is localized in the Coastal Plain Sands, Nanka Sands, and Nsukka Sandstone of the Anambra-Imo basin region. The most affected deposits are unconsolidated or poorly consolidated and have short dispersion times. Public education is essential for a sustainable termination strategy, and collaboration between the government, donors, the private sector, and rural people is crucial.[19]

Gullies are widespread at mid- to high latitudes on the surface of Mars, and are some of the youngest features observed on that planet, probably forming within the last few 100,000 years. There, they are one of the best lines of evidence for the presence of liquid water on Mars in the recent geological past, probably resulting from the slight melting of snowpacks on the surface[20] or ice in the shallow subsurface[21] on the warmest days of the Martian year. Flow as springs from-deeper seated liquid water aquifers in the deeper subsurface is also a possible explanation for the formation of some Martian gullies.[22]

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  A gully in Saratov Oblast, Russia.
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  Inside the gully (to the left) in Saratov Oblast, Russia.
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  Voçoroca (Portuguese for gully) in Avaré, Brasil
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  Gully formed from volcanic sedimentation in West Java, Indonesia
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  A Gully formed by flood in Isuaniocha community of Anambra State, Nigeria

• Oxford English Dictionary