Geo-environmental factors controlling gully distribution in a Mediterranean environment – a case-study in central Portugal

Abstract

It is known that gullies are forms of erosion that contribute to soil loss and degradation, especially in environments where soil conservation is difficult, as is the case in Mediterranean environments. It is therefore not surprising that great efforts have been made to understand and quantify the processes of water erosion associated with gullies. The study was carried out with the aim of identifying the main factors controlling gully formation in the Centre of Portugal. Thirty-eight gullies were identified, covering an area of 11 square kilometres, located on very deep blankets of alteration. The average length, maximum width and average width of the gullies are close to 105 m, 6.8 m and 3.8 m, respectively. The Group Analysis (GA) identified two groups of gullies, differentiated on the basis of morphological and geoenvironmental aspects. The Gr1 group includes larger gullies located on steeper slopes. The GR2 gullies are located at higher altitudes and on less steep slopes. Principal component analysis (PCA) identified slope, roughness index (IR) and fire severity after one year (SIa1a) as the main controlling factors. Given the size of the gullies and the likelihood of recurrent forest fires affecting the study area, some vital gully erosion control practices should be implemented as a matter of urgency.