Analysis of spatial and temporal variation characteristics and coordination of water-sediment in the north main reach of Yellow River

In order to investigate the temporal and spatial variations patterns and trends of runoff and sediment in the northern main reach of Yellow River, by adopting various methods including Mann-Kendall test, abrupt change analysis, wavelet analysis, and coordination analysis of water-sediment relationship, this study analyzed the variations of water and sediment for the hydrological stations of Toudaoguai, Longmen and Tongguan, based on the water and sediment data along the northern reach of Yellow River from 2002 to 2021. The findings revealed that the unevenness and concentration of sediment were greater than those of runoff, and the intra-annual characteristic variations exhibited more significant. Concentrated period for runoff was primarily in September, while sediment was mainly concentrated in August and September. Significant abrupt changes in water-sediment characteristics occurred in 2005 and 2017, which may be related to the regulatory impact of large-scale water conservancy projects in recent years. The dominant periodicities for water-sediment sequences were found to be 13 years, 10 years, and 9 years for Toudaoguai, Longmen, and Tongguan stations, respectively. Before 2008, the water-sediment relationship indicated sediment dominance over water, while after 2008, the trend shifted to water dominance. Particularly, sediment yield coefficient at Toudaoguai remained consistently below 0.009, indicating the persistent water dominance. Overall, the trend showed a continuous increase in runoff while sediment witnessed a noticeable decrease, showing an increasingly significant trend towards runoff dominance over sediment.