Frequency analysis of gully development in the Tunisian semi-arid

Abstract

Gully erosion represents an important risk in Mediterranean countries, especially in central Tunisia due to climatic conditions and human activities. The objective of the present study is to predict the gully erosion process in the Merguellil watershed, a representative of the Tunisian semi-arid area. The method employed to calculate the probability of gully occurrence is based on the use of a GIS environment and the frequency ratio (FR) method, using Support Vector Machine (SVM) to extract gullies from the Sentinel multispectral image, as well as 16 factors involved in gully erosion. Results show that more than 20% of the total basin area is vulnerable, that could increase the current gully network by more than 155 km. The likelihood of gully occurrence increases with topographic slope, especially in the presence of rocks with a underdeveloped soil texture. Furthermore, agricultural land use can also influence gully formation, especially in cultivated and rangeland areas. The study showed that gully susceptibility mapping can be automated by combining the gully inventory and the frequency ratio, thus producing useful maps for land management and conservation.

Keywords: Remote sensing, gully erosion, probability of occurrence, Tunisian semi-arid area, frequency analysis