Complex relationships between water discharge and sediment concentration across the Loess Plateau, China

Haiyan Zheng, Chiyuan Miao, Juying Jiao, Alistair Borthwick

Research output: Contribution to journalArticlepeer-review

Abstract

Understanding the relationship between water discharge (Q) and suspended sediment concentration (SSC) across the Loess Plateau is a prerequisite for evaluating soil and water conservation measures. Using daily Q and SSC datasets, this study jointly analyzes changes in Q and SSC on the central Loess Plateau, a major sediment producing area of China, during the periods 1971–1987 (P1) and 2008–2016 (P2). The results show that during both P1 and P2, the contribution of the maximum-3-day-per year sediment load to the total annual sediment load (SSL) is almost invariably over 50% (dominant), and in the majority of cases, the size of this contribution increases further between P1 and P2. The contribution of extremely high SSL events plays an overwhelming role in watersheds of area < 10,000 km2 and appears to be almost independent of change in land cover condition. In the Helong section of the Yellow River, there is more evident reduction in SSC than Q between these two periods (streamflow became clearer), while the opposite occurred in the Jing River (streamflow declined). In addition, the range of variation in SSC is large for small Q values, whereas the SSC for flood events tends to be relatively stable in gullied-hilly and flat-surfaced (Yuan) loess areas, which are major sediment producers. Based on scatter plots of SSC versus Q after logarithmic transformation, we find that the lower boundary of the mapped data points for an individual station fits a straight line. This boundary relates to riverbed erosion. Given that soil erosion weakened on gully slopes over time and streamflow in channels during P2 was generally lower, the boundary tended to move downward between P1 and P2 for most watersheds, reflecting a reduction in SSC for a given value of Q in P2 compared to P1.
Original languageEnglish
Article number126078
Number of pages55
JournalJournal of Hydrology
Volume596
Early online date16 Feb 2021
DOIs
Publication statusPublished - May 2021

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