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在规程中所列确定桥前壅水的公式中含有经验系数η,该系数取决于河滩的宽度。公式的基本表达形式为: Δh=1/2g(v_M~2-v_б~2) (1) 该式是在下列假设条件下对水流收缩段上下断面采用伯努里方程式的结果获得的: 1)在被观察的河段内由于横跨河槽的桥梁的约束而引起的局部水头损失不考虑。 2)对于指定断面的动能修正值取等于1,也就是α_M=α_б=1。
The formula for determining pre-bridge slugs listed in the protocol contains the empirical coefficient η, which depends on the width of the riverbank. The basic expression of the formula is: Δh = 1 / 2g (v_M ~ 2-v_б ~ 2) (1) This formula is obtained under the following assumptions on the upper and lower sections of the water flow contraction section using Bernoulli’s equation: 1) Local head losses due to the constraint of the bridge across the fluvial in the observed section are not considered. 2) The kinetic energy correction value for a given section is taken as 1, that is, α_M = α_б = 1.