Ephemeral gully and gully erosion in cultivated land: a review

Soil erosion has been recognized as the major cause of land degradation worldwide. The quantification of soil erosion is an important requirement for representing land degradation processes. One of the crucial points attracting an increased amount of attention in recent years is constituted by the possible discrimination of the different forms of soil erosion. In these contexts, relatively few studies have been conducted on channel erosion that still require improvement and elucidation, though most research and models proved to be very effective in providing useful information about surface erosion rates (rill-interrill). Erosion due to concentrated flow is severe on many unprotected farm fields across different countries of the world. The presence of various gully types (ephemeral, permanent, etc.) can be observed in different land uses and climatic conditions. The formation and development of channels, called ephemeral gullies, routinely obliterated by tillage and other farm operations, , constitute a severe problem in many cultivated fields. In fact, crops are washed out by scour as these small gullies form, and the crops at the lower end of the gully are submerged by the sediments from the ephemeral gullies. These filling operations reduce the long-term productivity of farmlands. Ephemeral gullies rapidly evolve in permanent gullies and contribute to the catchment rill network formation. They constitute effective links for transferring the runoff and sediment from uplands to valley bottoms and contribute to the denudation processes. Ephemeral gullies may also generate new badlands and aggravate the off-site effects of water erosion. The data available on gully erosion is scarce and usually restricted to small areas in which measurements are carried out over short time periods. The objective of this paper is to review recent studies on the different aspects of gully erosion, which are: • the morphological characteristics of gullies in comparison to the characteristics of other erosion channel types, including rills and streams; • the contribution of the gully erosion to overall soil loss and sediment production; • the analysis of some controlling factors; • and the models currently available to predict gully erosion.