Spatial scale dependence of sediment dynamics in a gullied rolling loess region on the Loess Plateau in China

Abstract

Sediment dynamics is still imperfectly understood, especially at spatial scale in the highly erodible region of the Loess Plateau, and few studies have been heretofore conducted. Using 5-year continuous water and sediment records, three plots and three basins in the gullied rolling loess region were selected and sediment dynamics at spatial scale was studied. Results showed that the floods, where the peak discharge (Q p ) did not come earlier than the sediment peak, were predominant in slope zones, occupying [90 and [70% of the total for the Mao slope and for the Entire slope, respectively. However, in basins, most of the sediment peaks (C p ) lagged behind Q p , implying that slope zone was the main origin of sediment. More than 50% of the events presented clockwise hysteresis loops in the Mao slope area, while almost all the events had anticlockwise hysteresis loops in basins. This can be attributed to less occurring frequency of hyperconcentrated flow, as well as its instability in slope zones, compared to those in the basins. Within these contexts, gravitational erosion made the highest sediment concentration (C) in Tuanshangou basin and median developing status of C-discharge (C-Q) relationships in the Entire slope area. This study provides insights into the protection of slope surface and disruption of the development of hyperconcentrated flow to reduce soil loss.

Seasonal Accumulation and Depletion of Local Sediment Stores of Four Headwater Catchments

“…Rodriguez-Blanco et al [6] similarly found clockwise to be the dominant hysteresis pattern suggesting a localized sediment sources. In contrast to these findings, Fang et al [14] showed clockwise patterns at the hillslope plot scale and counterclockwise patterns at the basin scale suggesting a dominantly hillslope source at various spatial scales on the Loess Plateau of China. The difference in results between this work and Fang et al is likely because their site has some of the highest soil erosion rates in the world with an average annual sediment yield of 22,200 tons per km 2 and extremely steep slopes of up to 70 degrees [14].…”

“…In contrast to these findings, Fang et al [14] showed clockwise patterns at the hillslope plot scale and counterclockwise patterns at the basin scale suggesting a dominantly hillslope source at various spatial scales on the Loess Plateau of China. The difference in results between this work and Fang et al is likely because their site has some of the highest soil erosion rates in the world with an average annual sediment yield of 22,200 tons per km 2 and extremely steep slopes of up to 70 degrees [14]. In comparison, sediment yields in the central Sierra Nevada have been estimated to be around 4.1 tons per km 2 [3].…”

“…However, much of this work has been focused on individual discharge events [10][11][12], or has been in predominately agricultural areas [4,6,7,[11][12][13], in small hillslope plots [11] or in areas with drastically different physiographic and climatic regimes [7,14,15]. A few longer studies looking at multiple time scales have shown considerable temporal variation in sediment patterns.…”

“…They found that more sediment moved during the snow melt season than the rest of the year and that a shift from clockwise to counter-clockwise hysteresis patterns occurred as the snow melt season progressed. Fang et al [14] found differences in the sediment-discharge hysteresis patterns between the hillslope plot (clockwise) and small basin scales (counterclockwise) that implied a hillslope source area in the Loess Plateau of China. Headwater and larger order basins in southeast Australia were studied by Smith and Dragovich [17] who suggested that differences in sediment patterns were due to rates of sediment transfer to larger order basins.…”

Correlating check dam sedimentation and rainstorm characteristics on the Loess Plateau, China

“…During flood events, the relationship between sediment transport and discharge is not normally homogenous, often producing hysteretic loops (diCenzo and Luk, 1997; D'Agostino and Lenzi, 1999;Rickenmann, 2001;Seeger et al, 2004;Lefrancois et al, 2007;Rodríguez-Blanco et al, 2008;Soler et al, 2008;Mao et al, 2014), which have been identified between discharge and sediment transport on the Loess Plateau (Fang et al, 2008(Fang et al, , 2011(Fang et al, , 2015Fan et al, 2013). However, the role of hysteretic loops for check dams remains unclear.…”