河口附近之河段常受潮汐的影響,在此流況複雜之河段觀測流量時,傳統流量觀測的準確性並不高。感潮河段是屬於變量流,因此有必要利用高效率的流量觀測方法觀測流量。本研究分析淡水河流域的台北橋與關渡之流場資料,應用指標流速法來推估此感潮河段流量;並應用以機率觀念為基礎之流速分佈理論,求其完整之流速剖面於指標流速法。推估感潮河段流量需要三個程序:(1)建立水位(水深)與通水斷面積之率定曲線,(2)建立指標流速與斷面平均流速之率定曲線,(3)流量可由水位(水深)推估出來的通水斷面積與指標流速法推估之斷面平均流速之乘積求出。其結果顯示推估與實測流量十分接近;因此位於流況複雜之感潮河段應用量測快速且簡易之指標流速法觀測流量。
Measure discharge is inaccurately at estuary is affected by tidal. The tidal stream is unsteady, we need efficient method to measurement discharge. The study apply Chiu`s Velocity Distribution and Index-Velocity Method to estimate the discharge of tidal stream in the Taipei Bridge, the Guan-du. First, establish index-velocity need to build the relation between water level and cross-section area, and build the relation between the mean velocity and index velocity. Then the discharge could be estimated as the product between mean velocity and cross-section area. Accuracy and reliability of this method indicates that the discharges estimated by this method agree quite well with the observed discharges. The results provide evidence the index-velocity method can offer good performance in measuring discharge in tidal streams.