Critical topographic threshold of gully erosion in Yuanmou Dry-hot Valley in Southwestern China

Gully initiation has been a subject of much discussion in the field of gully erosion. Gully initiation could be examined by the S-Delta relationship (S = alpha Lambda(-b)) between the critical slope of the gully head (S) and the upstream drainage area (A). Gully erosion plays an important role in sediment yield and land degradation in the Dry-hot Valley region of Southwest China; however, little research has focused on gully development in this region. This study investigated gully morphology and the critical topographic threshold of permanent gullies in Yuanmou Dry-hot Valley. Data for 36 gully heads were derived from the gully digital elevation model created by high-precision real-time kinematic GPS (RTK GPS). A significant relationship between gully length and volume (r(2) = 0.77, p < 0.01) was found to exist, indicating that gully length can be used to estimate the gully erosion rate. Additionally, as vegetation coverage inside the gully increases, the gully morphology tends to be stable. The S-A relationship was S = 0.5195A(-0.0899), while AS(2) values ranged between 4.2 and 758.5 m(2). The low value of constant b (0.0899) indicates that collapse of the gully wall is the dominant process of gully erosion in Yuanmou Dry-hot Valley.