Ximeng Xu

Effects of rainfall regime and its character indices on soil loss at loessial hillslope with ephemeral gully

Understanding the relationship between hillslope soil loss with ephemeral gully and rainfall regime is important for soil loss prediction and erosion control. Based on 12-year field observation data, this paper quantified the rainfall regime impacts on soil loss at loessial hillslope with ephemeral gully. According to three rainfall parameters including precipitation (P), rainfall duration (t), and maximum 30-minute rainfall intensity (I30), 115 rainfall events were classified by using K-mean clustering method and Discriminant Analysis. The results showed that 115 rainfall events could be divided into three rainfall regimes. Rainfall Regime 1 (RR1) had large I30 values with low precipitation and short duration, while the three rainfall parameters of Rainfall Regime 3 (RR3) were inversely different compared with those of RR1; for Rainfall Regime 2 (RR2), the precipitation, duration and I30 values were all between those of RR1 and RR3. Compared with RR2 and RR3, RR1 was the dominant rainfall regime for causing soil loss at the loessial hillslope with ephemeral gully, especially for causing extreme soil loss events. PI30 (Product of P and I30) was selected as the key index of rainfall characteristics to fit soil loss equations. Two sets of linear regression equations between soil loss and PI30 with and without rainfall regime classification were fitted. Compared with the equation without rainfall regime classification, the cross validation results of the equations with rainfall regime classification was satisfactory. These results indicated that rainfall regime classification could not only depict rainfall characteristics precisely, but also improve soil loss equation prediction accuracy at loessial hillslope with ephemeral gully.

Gully morphological characteristics in the loess hilly-gully region based on 3D laser scanning technique: Gully Morphological Characteristics by 3D Laser Scanning Technique

Gully erosion plays an important role on sediment production in the Loess Hilly-gully Region. Gully morphology is strongly affected by the gully erosion process and can be used to describe the gully developmental condition. The Chabagou watershed, located in the hilly-gully region of the Loess Plateau, was selected to investigate gully morphological characteristics using a 3D laser scanning technique (LiDAR). We selected 31 representative gullies at active stages, including different watershed locations and gully orders, to quantitatively describe gully morphology and establish empirical equations for estimating gully volume based on gully length and surface area. Images and point clouds datum of the 31 gullies were collected and digital elevation models (DEMs) with 10-cm resolution were generated; then the gully fundamental morphological characteristics including gully length (L), gully width (WT) and gully depth (D), and some derivative morphological indicators including gully head curvature (C), gully width to depth ratio (w/d), gully bottom to top width ratio (WB/WT), gully surface area (Ag) and gully volume (Vg) were extracted from the DEMs using ArcGIS 10.1 (Table 1).