Abstract: In the 25-year period from 1972 to 1997, there were 20 years in which the Yellow River experienced flow interruptions. As a result of repeated flow interruptions, the river channel has shrunk steadily, leading the river to a new stage of development. Repeated flow depletion has added to the difficulty of flood control in the delta region and brought severe negative impact on it s environment. This paper examines the problems of flood control and water supply and their causes. A side from natural causes, human facto rs are especially impo rtant in the river’s flow interruptions. Among the majorreasons for flow depletion are little precipitation, reduced runoff volume, accelerated pumping for irrigation, flow detention by water and soil conservation measures, low capability of flow regulat ion by reservoirs, poor management and waste of water resources. In recent years, environmental changes in the Yellow River delta region are manifested in the following areas. First, the river channel has clearly shrunk and the water table has risen significantly. Three phases of sedimentation in the river channel can be identified. Sediments decreased during 1950～ 1960; they disp layed a U-shaped pattern in the 1964～ 1985 period; and they rose from 1986 to 1995. An understanding of the changes in the channel in the last phase can help us bet ter understand the current conditions of flood control in the lower reaches and the mouth of the river. The August 1996 flood level at Lijin Station reached 14. 7m , the highest ever recorded. This levelwas 0. 94m and 1. 19m higher than the levels for 1958 and 1992, respectively. If the river continues to experience flow interruptions, a discharge of 10⁴m³/s at Lijin may result in large-scale flooding, with the po ssibility that the river may shift its course. Second, the sho rtage of water for drinking and indust rial use has become increasingly serious in recent years. In 1992, there were 83 days in which the channel below Lijin dried up, causing critical shortage of drinking water for two million people and half a million livestock. In 1995, there were 122 days in which the channelwas dry, forcing a large number of indust ries to cease or reduce production and resulting in a loss of 600 million yuan. To ensure sufficient drinking water for humans, the amount of water charged too ilwells was reduced by 2. 6 million m³, causing a reduction of 3×10⁶ tons of crude oil production, or a loss of 216 million yuan. Third, pumping water from the river for irrigation has increased rapidly, from 6 billion m³ in the 1950s to 29. 8 billion m³ in the 1990s, the latter being 50 percent of the river’s annual natural runoff. Fourth, soil and water conservation uses about 2. 8 billion m³ of water per year, which accounts for 9 percent of the average annual runoff of 30. 7 billion m³ fo r the 1986～ 1994 period. Fifth, the capability of water regulat ion by reservoirs is quite low. The reservoir at Sanmen Go rgeat the beginning of the flood season (June) can only hold 1. 4 billion m³ of water. Lastly, poor management and serious waste of water are also reasons for repeated flow interruptions in the river.

Key words: flow breaking in the lower Yellow River, delta, flood control, environment, bad effects