Identification of tableland and evaluation of sediment yield in the Loess tableland gully area

BackgroundSince 2000, the amount of sediment from the Yellow River has significantly decreased. The average annual sediment yield at Tongguan Hydrological Station has decreased from 1.344 billion tons before 2000 to 245 million tons between 2000 and 2019, a decrease of 81.79%. More than 90% of the sediment in the Yellow River comes from the loess hilly gully area and the loess tableland gully area, and there is a significant difference in the reduction of sediment inflow between the two regions.Methods To study the sediment yield situation in the loess tableland gully region, The 20 hydrological units concentrated on the loess tableland gully area were selected as the study area. The fragmentation index (Meff) was introduced to evaluate the degree of tableland fragmentation, and the relationship between Meff and sediment yield was analyzed to construct a sediment yield model for the loess tableland gully area.Results Meff ≥ 100 is considered a complete tableland,50 ≤ Meff ＜ 100 is a hilly tableland（Slightly fragmentized tableland）,Meff < 50 is considered a fragmentized tableland.Meff is highly negatively correlated with the actual measured sediment yield/the sediment yield calculated using sediment yield model in the Loess hilly gully area, with a coefficient of determination R2 of 0.9649.Based on this, established a Meff based sediment yield model for the loess tableland gully area. In 2025, 2030, 2035, and 2050, the total sediment yield of tablelands with Meff values greater than 50 will decrease by 8.38%, 14.66%, 19.85%, and 31.44% respectively compared to 2018. There is no significant change in sand production modulus and sediment yield from 2025 to 2050. If terraced fields and forests and grasslands are deployed in the loess hilly gully area, the reduction in sediment yield can be as high as 13.2%, 22.30%, 29.65%, and 45.08%, respectively.ConclusionThe sand reduction effect of terraced fields and forest grasslands in the loess tableland gully area is significantly lower than that in the loess hilly gully area.Protecting the surface of the tablelands, preventing the concentration of runoff into the ditch, and implementing efficient rainwater harvesting and utilization technologies are the directions for future governance and research.The research results are of great significance for the prevention and control of soil erosion, major engineering decision-making, and the study of water and sediment changes.