Numerical Modeling And Analysis Of The Outfall Reach Of Huaihe Floodway

The Huaihe River's floodway toward Huanghai Sea was not adequate in the past years. The huge runoff in the flood season had badly endangered the lives and fortunes of over 2000 million residents in downstream region of Huaihe River. It is necessary and pressing to excavate and broaden the floodway to increase the capacity of flood discharge and enhance the standard of flood control. This thesis numerically modeled the current hi the outfall reach of a new floodway, and provide the scientific basis for the layout and design. It was first to derive the control equations of numerical models based on the past relevant achievements, and the common numerical-computation methods were introduced and compared after that 1-D and 2-D models were both applied according to the condition of the problems. The 1-D model program was the FLORIS that have been broadly used to model networks of river, and the 2-D model used FASTTABS, a good visualized program package suitable for modeling the shallow waters.The computing results show that the current hi the outfall reach moves periodically because of the sea tide, but the influence decrease upstream. The discharge capacity decrease and the water level rise as the floodplains' roughness increase. Both the tide and the increase of floodplains' roughness can change the diffluence ratio between northern and southern branch. Though the water levels cross one section are almost equal, the velocities differ greatly. At the some cross-section, the velocity in the in the quirk may be double as that on the floodplain. The water surface will rise hi the southern branch because of the improper diffluence ratio, if using the designed diffluence col. When the southern branch discharge about 800m3/s, the water flow can be improved.The thesis not only concluded the current movement rules, but also explained many problems brought forward from engineering. It was specially pointed out that, when the tail water is constant maximum tide, the computed flood surface is higher than that of nonsteady current, so there is some safety superelevation. Underestimation of the roughness will make downward bias to compute along-river surface and bring hidden trouble for flood control. To improve the section can decrease the water level or offset the water rise for increase of floodplains' roughness, but it need much engineering works. Therefore, it's more worthwhile to maintain the floodplain's bed clear.