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[Objective] The purposes of this study are to elucidate the long-term trends and periodic characteristics of runoff in the Dagu River Basin, and to offer the theoretical insights to guide water resource management and promote sustainable development in the Dagu River Basin. [Methods] The measured runoff data from the Nancun Hydrological Station（1956—2020） and the Zhazi Hydrological Station（1956—2016） were used to analyze the trend of annual runoff changes and abrupt change times using the Mann-Kendall test and sliding t-test. The Morlet continuous complex wavelet method was used to analyze the periodic characteristics of multi-year runoff in the basin. [Results] The annual runoff in the Dagu River Basin was generally declining, and there was a characteristic of more flow during the flood season（June—September） and less flow during the non-flood season. The peak flow usually occurred in August. The runoff of Nancun Station was abrupt in 1976, and the runoff of Zhazi station was abrupt in 1979. The runoff of the Dagu River Basin exhibited significant periodic variations at multiple time scales, with a dominant period of around 20 years, and significant oscillations before the 1980s. [Conclusion] The long-term series runoff of Dagu River Basin showed a trend of significant decline, and the basin runoff suddenly changed in the 1970s, and there were periodic changes in different time scales. In the future, the research on the mechanism of runoff change should be strengthened. [ABSTRACT FROM AUTHOR]

Factors affecting the flocculation and settlement of sediment in the Yellow River estuary include sediment concentration, sediment particle size, temperature, salinity and turbulent shear force. Based on the previous research results, combined with the fractal theory of sediment flocculation and the modified particle size of flocculation, a more accurate formula for calculating the sedimentation velocity of flocs was derived. At the same time, in order to verify the applicability of the theoretical formula, a static water settlement experiment was carried out on viscous fine sediment particles at the mouth of the Yellow River. The experiment was carried out with the help of laser particle size analyzer and a new type of temperature controlled rectangular settlement barrel. The sedimentation process was analyzed and predicted by using the biased normal distribution model, and the sedimentation velocity and its variation with salinity and sediment concentration in the Yellow River estuary were clarified. [ABSTRACT FROM AUTHOR]