The cover image, by Baojun Zhang et al., is based on the Research Article Impacts of headcut height on flow energy, sediment yield and surface landform during bank gully erosion processes in the Yuanmou Dry-hot Valley region, southwest China, https://doi.
Soil erosion in hilly areas of the Sichuan Basin is a serious concern over sustainable crop production and sound ecosystem. A 3-year experiment was conducted using the method of runoff plots to examine the effects of terracing and agroforestry in farmland systems on soil and water conservation of slope fields in the hilly areas in Jianyang County, Sichuan Province, Southwestern China. A power function (Y = aX b ) can statistically describe the relationship between water runoff (Y) and rainfall (X). The regression equation for the treatment of sloping terraces with crops (Plot 2) is remarkably different from that for the treatment of sloping terraces with grasses and trees (Plot 1) and the conventional up-and down-slope crop system (Plot 3) regarding equation coefficients, while regression equations are similar between Plot 1 and Plot 3. Water runoff amount and runoff coefficient of slope fields increased by 21.5~41.0 % and 27.5 ~ 69.7 % respectively, compared to those of sloping terraces, suggesting that terracing notably reduced the water runoff in the field. In the case of sloping terraces, lower amount of water runoff was observed on sloping terraces with crops than on sloping terraces with grasses and trees. Sediment yields on the slope fields in the normal year of rainfall distribution were notably higher (34.41 ~ 331.67 % and 37.06 ~ 403.44 % for Plot 1 and Plot 2, respectively) than those on sloping terraces, implying that terracing also plays a significant role in the reduction in soil erosion. It is suggested that terracing with crops is significantly effective for soil and water conservation in cultivated farmland, while the conventional practice of up-and down-slope cultivation creates high rates of water runoff and soil sediment transport. Terracing with grasses and fruit trees shows a less reduction in water runoff than terracing with crops, which was observed in the 3-year experiments.
Gully initiation has been a subject of much discussion in the field of gully erosion. Gully initiation could be examined by the S-A relationship (S = aA Àb ) 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 À0.0899 , 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.
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