Experimental study of shallow mass movements on gully slopes and associated sediment under rainfall on the Chinese Loess Plateau

ABSTRACT Mass movements on gully slopes are the main contributors to gully-bank expansion and are the major source of sediment delivered to rivers; however, they are often overlooked because they are either too small or too time‐consuming to measure in the field. To resolve this challenge, a novel topography meter was used to observe shallow mass movements on the gully slopes of the Loess Plateau under simulated rainfall. The experiment showed that the cumulative shallow mass movement volume logarithmically increased with the rainfall amount. The critical rainfall for shallow mass movement occurrence was about 28 mm at a rainfall intensity of 50 mm h−1. The results also show that soil water content was a key element controlling the occurrence of the shallow mass movements, and the minimal soil water content for permitting shallow mass movements was about 23.1-25.6% for 10-20 cm deep soil. Shallow mass movement on gully slopes has a significant influence on sediment yield. The sediment concentration and sediment transport rate during mass movement failure were on average 3.6 times and 4.0 times higher than that during pre-failure events, respectively. Our results have important implications for understanding the connectivity of sediment discharge and mass movements on gully slopes in hilly and gully watersheds.