圖書典藏及影音數位平台

曾文溪於洪流之水流湍急，中高流量下觀測垂線流速剖面不易，為準確推估洪水流量，需探求表面流速與垂線平均流速之關係，依據現地試驗成果，由觀測表面流速與垂線平均流速合理推求兩者比值，分析檢定適合曾文溪之河床阻力公式，提供本局未來決策之參考。

Hydrographic data are the important basis of basin management, disaster warning, framed water resource plan and the design of engineering planning. Discharge is the most important of hydrographic data, because it will affect the results of water resource deployment and flood-mitigation engineering. Therefore, discharge measurement is important in hydrological observation work. The accuracy of discharge measurement will be affected by measure technology, measurements of river, flow characteristics and the conditions of cross section. In order to promote measure technology and data accuracy, the project draw up new discharge measurement method by refer new measurement technique. Furthermore, we verify the applicability of new measurement method, and discuss the relationship between mean velocity and surface velocity. In the plan, we calculate the roughness coefficient of SIN-JHONG station, ZUO-JHEN station, YU-TIAN station, YU-FONG bridge station and ER-CI bridge station by river bed material sampling. We formulate new measurement method by study measurement instrument and method. We recommend use ADV and ADCP to measure discharge in low discharge and high discharge respective, and use flood discharge measurement to verify the applicability of new measurement method in different flow condition. In this project, we estimate theoretical relationship between mean velocity and surface velocity by log-law and power-law, and compare with field experiment data. The results show the ratio of mean velocity with surface velocity will increase with water depth, and the trend is similar with log-law. The ratio of mean velocity with surface velocity are get by regression analysis, the value of SIN-JHONG station is 0.83, ER-CI bridge station is 0.8, ZUO-JHEN station is 0.79, YU-TIAN station is 0.84, YU-FONG bridge station is0.89. In this plan, we use ADCP to measure flood discharge in SIN-JHONG station, the maximum discharge is 1189cms, and establish the water level-discharge rating curve of SIN-JHONG station. The velocity profile in floodplain, outside floodplain and main channel are different. In floodplain, the velocity profile similar to log-law, the secondary currents occur in outside floodplain. Furthermore, the measure results show that the velocity distribution in main channel are complicated, because the flow in main channel is affect by the pier, and the velocity profile is different from log-law. In low water level, the velocity profile in YU-TIAN station, YU-FONG bridge station and ZUO-JHEN station are similar with log-law. Furthermore, the velocity profile in ER-CI bridge station is different from log-law because of backwater occurs in downstream.