Daily Variations of Water Discharge and Sediment Discharge Into the Sea from Yellow River from 1950 to 2000 and Relevant Influential Factors That Generate These Changes

This paper analyzes the daily variations of the water discharge and sediment discharge through Lijin Hydrologic Station from 1950 to 2000, and indicates the extreme circumstances including the processes in which the flood peak and sediment peak decreased and disappeared in the past 51 years. This paper also demonstrates the changes and laws of the water and sediment discharge flowing into the sea. The result displays that, with the sharp decrease of the yearly average volumes of water and sediment discharges, the number of days with daily discharge under 500m3/s was over three times greater in the 1990s than in the 1950s, the flood discharge surpassing 2 000m3/s frequently occurred at the earlier stages but disappeared in 1997, the flood peak discharges over 4 000m3/s have disappeared since 1989 and those exceeding 6 000m3/s have disappeared since 1986. At the same time, the daily average sediment discharges surpassing 500t/s occurred before 1989 and those exceeding 700t/s disappeared after 1977. The number of days when the daily average sediment content was over 80kg/m3 and probably generated Hyperpgenal plumes gradually decreased in the past 51 years. The water consumption increase and the large and medium-sized reservoirs built in the river mainstream have negative effects on the water and sediment discharge. Both the sharp decrease of the water and sediment discharges and the extreme circumstances such as flood peak and sediment peak have a great negative effect on the estuarine evolvement and estuarine ecological environment.