Abstract. Gullies are one of the most relevant erosion processes, connected to land degradation and desertification, in special in arid and semiarid regions. Despite its role, gully erosion is neglected by many models and researches. This study presents a physically-based model for small permanent gullies, typical in the Brazilian Semiarid Region. The model consists of coupling two previous models, those by Foster and Lane (1983) and Sidorchuk (1999). As both models require input data of peak discharge and duration, different rain intensities were tested. The rain intensity that suited gully erosion modelling best was the 30-minute intensity. The Foster and Lane model supplied a better response for smaller areas, where bed-channel erosion is more pronounced. The Sidorchuk model presented a better performance in larger sections, where wall erosion becomes more prominent. The experimental area is located in the semiarid State of Ceará, Brazil, in which the land use is characterised by agriculture and livestock. We measured and modelled three gullies ageing almost six decades. The threshold between the prevailing domains of each process (channel bed or wall erosion) is based on the cross-section area; and it is intrinsically connected to wall erosion: for the case study, the threshold area was approximately 2 m2. The final model, hereby called FL-SM (Foster & Lane and Sidorchuk Model) performed very well, with Nash–Sutcliffe coefficient of 0.846.
Physically-based model for gully simulation: application to the Brazilian Semiarid Region
