描述黄河中下游河道横断面形态的新指标

描述河流横断面的窄深程度,无非是用来衡量它对过流能力和输沙能力的影响大小,及其在河流地貌方面的时空上的调整变化。回顾总结了以往描述横断面形态的常用指标,包括河相系数、宽深比,或湿周与平均水深的比值,指出这几种指标在描述黄河中下游河道时所存在的共同缺点:(1)缺乏物理意义;(2)不能真正代表断面的窄深程度;(3)明显的夸大了宽浅和窄深断面的差别。从表称流量的概念出发,作者认为,应该使用具有明确物理意义的等面积的表称流速来描述断面形态。如果用表称流速来衡量黄河下游河南和山东河道的断面形态的差别,就会发现,断面形态的不同,其对过流能力的影响不过1:2,远不象河相系数和宽深比所描述的达到1:6甚至1:11那样的悬殊程度;黄河下游河道主槽“多来多排”的主要影响因素是表称流速。

New Indicators to Characterize the Natural River Channel Cross-Section Shape

The aim of characterizing the narrow to width degree of river cross-ection is to judge its flow and sediment conveyance capacity as well as its temporal and special gee-morphological adjustment and changes. After analysis of the classical indicators used to describe river cross-section Shape, such as are fluvial facies coefficient, width to depth ratio, the ratio of wetted perimeter over average depth, the common drawbacks of the classical indicators were concluded as following; (1) lack of clear physical meaning; (2) difficult to represent the actual narrow to width degree of cross-section; (3) apparently overestimate the difference between broad and shallow cross-section with narrow and deep one. Derived from the concept of nominal discharge, it was pointed that it should use the nominal velocity of equivalent cross-section area, an indicator with clear physical meaning, to characterize the cross-section shape and morphology. It is found that the effect of river cross-section difference in Henan and Shandong on channel conveyance is less than 1:2, whose conveyance differeoee is not as sharp as 1: 6 or 1:11 calculated by using fluvial facies coefficient or width to depth ratio correspondingly. And it is also found that the primary factor influence on the characteristics of Yellow River sediment conveying known as the more sediment input and the more sediment output in main channel is nominal velocity.