The reductions of runoff and sediment load in the Haihe River Basin and the causes of the shrinkage of the estuarine channels are analyzed in this paper it is concluded that the modern Yellow River sediment can be transported to the south part of the Bohai Bay, but rarely to the north part and the Tianjin Harbor. Sediment from the mid of the Bohai Bay does not affect the estuarine channels. The sediment caused the estuarine channels shrinkage are from the modern and ancient Yellow and the Haihe River deposit removed by wave. tidal current, and beach erosion. The influences of the estuary shrinkage on the flood discharge capacity of the river mouth channels and the flood hazard are discussed. The maximum capacity of the reservoirs and pools is about 20 billion m^3 in the south part of the basin while the capacity in the north part is only 7.5 billion m^3. Two 100 years floods occurred in the watershed in 1963 and in1996 with total runoff about 30 billion m^3 each. The economic loss in 1996 is about $6 billion, nearly two times of that in 1963 in the south part of the area. One of the main reasons is that the discharge capacity of the channels in the area had reduced by 50%. If another 100 years flood occurs in the south part again, the economic loss will be similar to that in 1996. If a 100 years flood occurs in the north part, the economic loss will be much higher than that in 1996. Because the storage capacity of reservoirs and pools in the area is much less than that in the south area. and discharge capacities of the north estuarine channels decreased more sharply than that of the south. Strategies for controlling estuary shrinkage are suggested. Physical and mathematical models show that trailer dredging combined with scouring with runoff or tidal water is economical and practical. Guiding dikes at the river mouths to prevent turbidity water entering into the estuarine channel will be a major strategy. Building a new gate combining the harbor may also mitigate the sedimentation of the mouth channels.
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