Alleviated Water-sediment Imbalance in the Middle Yellow River evaluated by hysteresis patterns

Purpose This study aims to investigate the process-based imbalance between water flow and sediment in the Middle Yellow River. The main research questions are: (1) a better method to evaluate the temporal synchrony between the hydrology and erosion processes, and (2) the change of water-sediment relationship following ecological remediation in the Middle Yellow River. Methods Data from experimental plots and hydrology stations of the Middle Yellow River has been collected. More than 780 flood event data were collected from experimental plots to evaluate the availability of different methods for calculating hypothesis index and to find a better method to evaluate the process-based sediment transport. Methods of Lawer and Aich were selected to evaluate the process-based hysteretic of the water-sediment relationship in experimental plots. Month scale data of more than 70 hydrology stations in the Middle Yellow River were collected to evaluate the change of water-sediment relation following ecological remediation in the Middle Yellow River. Results Analysis showed that hypothesis index evaluated by Aich method is much more stable, and can be used to compare different flood events and between different watersheds. Besides, the discharge interval of 25% is enough for evaluating the process-based sediment transport. Monthly data of hydrology station shows that, in the Middle Yellow River, the average hypothesis index value decreased from 0.15 to 0.11, while the dominance of sediment transport during the high-flow period over the low-flow period has decreased by 27%. Conclusions Ecological remediation has alleviated the water-sediment imbalance in the Middle Yellow River. However, the alleviation varies in different watersheds.