Critical condition and specific-energy diagram for compound channel with sloping flood-plains

• Main Authors: Chih-Cung Chang, 張志宏
• Other Authors: Chan-Ji Lai
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/21076471776356785022

碩士 === 國立成功大學 === 水利及海洋工程學系 === 88 === Previous researches on compound channel hydraulics were mostly conducted in channels that had horizontal flood plains. In these channels the hydraulic properties are shown to be discontinuous at over-bank stage. But in natural channels the floodplain are usually inclined due to flow and channel bed interactions. This study thus conducts analytical analysis to sloping flood plain compound channels (SFPCH). Mathematically this analysis is possible and is more pertinent to real cases. A critical condition parameter   Qc2/(gy15), y1 being the main channel depth, is used so the critical conditions for a channel with a given discharge can be easily and accurately obtained. Two  values,  minimum (min) and  maximum (max), are obtained. Below min there is only a critical depths, yc occurs in main channel. Above max there is only a yc occurs above the bank-full stage. Between these two three ycs can occur.This results are very comparable with those of the Chaudhry and Bhallamudi (C&B;1988) findings. Moreover, it is interested to see that at min there are only two ycs can occur, below and above the bank-full stage. Critical condition has practically been used for discharge measurement applications. Only one critical depth for a given discharge is essential in these applications. This analytical analysis shows that the geometry of main channel is important in this issue. For a main channel with large aspects ratio, say greater than 11, one discharge for on critical depth is possible if the inclination of the flood plain is set at 1度.