Flow resistance equations for gravel- and boulder-bed streams
Flow resistance equations for gravel- and boulder-bed streams
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DOI：
10.1029/2006wr005422
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发表时间：
2007-05-22
影响因子：
5.4
通讯作者：
Ferguson, Rob
中科院分区：
文献类型：
--
作者：
Ferguson, Rob
[1]在砾石床和砾床溪流的相对淹没范围内，为预测平均流速，可考虑其他一般形式的方程。提出了一些以前的半经验模型和物理概念的部分统一。提出了两种新方程：深层和浅层流动的不同参数的无量纲水力几何方程和浅层流动的渐近于粗糙层公式和深层流动的对数摩擦律的Manning-Strickler近似的变功率阻力方程。利用D-84作为粗糙度尺度的现有方程和新方程的预测结果，与在相对淹没0.1至30以上的自然溪流中测量到的速度汇编进行了比较。变幂方程的性能与现有的最佳方法（带粗糙度乘数的对数律）相当。在预测已知流量或假定流量如何在深度和流速之间划分时，无量纲水力几何方法优于使用相对淹没度的方程。由于对深度、速度和坡度的操作定义的敏感性，使用单一粒度长度尺度的不充分，以及陡峭浅流中流动物理的复杂性，所有方法都会出现二因子预测误差。
[1] Alternative general forms are considered for equations to predict mean velocity over the full range of relative submergence experienced in gravel- and boulder-bed streams. A partial unification is suggested for some previous semiempirical models and physical concepts. Two new equations are proposed: a nondimensional hydraulic geometry equation with different parameters for deep and shallow flows, and a variable-power resistance equation that is asymptotic to roughness-layer formulations for shallow flows and to the Manning-Strickler approximation of the logarithmic friction law for deep flows. Predictions by existing and new equations using D-84 as roughness scale are compared to a compilation of measured velocities in natural streams at relative submergences from 0.1 to over 30. The variable-power equation performs as well as the best existing approach, which is a logarithmic law with roughness multiplier. For predicting how a known or assumed discharge is partitioned between depth and velocity, a nondimensional hydraulic geometry approach outperforms equations using relative submergence. Factor-of-two prediction errors occur with all approaches because of sensitivity to operational definitions of depth, velocity, and slope, the inadequacy of using a single grain-size length scale, and the complexity of flow physics in steep shallow streams.