河道束窄段对上游洪水过程特性的影响

为了研究束窄河段对洪水演进过程特征的影响，采用二维全水动力模型GAST模拟了束窄段河道洪水过程，通过理想河道和灞河上游实际河道分析了河道束窄程度与洪水特性间的定量关系。结果表明：束窄断面形状对洪水过程特征中水深、流速影响的大小依次为V形>U形>梯形>矩形。断面形状相同时，束窄程度越大对水深和流速影响越大。河道束窄段上游水位壅高，下游水位相对降低但流速更大。扩宽河道束窄段可以降低上游水位及上下游流速差。在“8·19”洪水下，灞河束窄河段束窄程度降低时（原河道束窄程度为64.4%，河道疏浚后束窄程度分别为55.6%、46.7%、37.8%），上游最大水深分别减小0.669、0.985和1.066 m，上下游流速差分别减小0.702、1.592、2.550 m/s。洪量越大则河道水位越高、流速越大，束窄程度变化对水位和流速变化的影响也越大。将“8·19”洪水进行缩放入流情况下，原始河道最大水深分别为2.177、2.778、3.618 m，束窄程度为37.8%时最大水深减小至1.866、2.367、3.175 m。通过分析不同束窄程度的束窄段河道洪水过程特性，可为束窄段河道防洪提供参考。

Influence of narrow river reach on flood hydraulic characteristics

In order to study the influence of narrow river reaches on flood evolution, the two-dimensional all-hydrodynamic model GAST was used for numerical simulation, with which the quantitative relationship between the narrowing of the river reach and the flood hydraulic characteristics of the ideal river and Bahe River was analyzed. The results show that the influence of the narrow section shape on water depth and flow rate in the flood evolution process in decreasing order is: V-shaped, U-shaped, trapezoidal and rectangular. When the shape of the sections are the same, the greater the narrowing of the section, the deeper the influence on water depth and velocity. The water level in the upstream of the narrow reach is higher than that in the downstream, but the velocity is on the opposite, so broadening the narrow reach can reduce the difference of water level and velocity between the upstream and downstream. Under the flood 8·19, the upstream water depth of the three working conditions (original narrowing degree is 64.4%, after dredging the narrowing degree of the three working conditions become 55.6%, 46.7% and 37.8% ) can be reduced to 0.669, 0.985 and 1.066 m, and the flow velocity difference can be reduced by 0.702, 1.592 and 2.550 m/s. When the flood volume increases, the water level and flow velocity of the river increase, so does the influence of narrow reach width change on water level and velocity. Under the three inflow conditions, the maximum water depth of the original reach is 2.177, 2.778 and 3.618 m, and the maximum water depth is reduced to 1.866, 2.367 and 3.175 m after increasing the narrowing degree to 37.8%. The analysis of hydraulic characteristics of the narrow river reach with different narrowing degrees can provide a reference for the flood control of narrow river reaches.