本文利用實驗來模擬水流通過不透水式橋墩保護工的流況，針對保護工頂部及上下游的流速分布進行量測，並加入前人有關於透水式橋墩保護工的研究數據，進行比較分析。對透水式橋墩保護工在接近底床處因粗糙關係使得對底床的流速有拖曳效應，讓流速減小，而透水式與不透水式橋墩保護工均因束縮的緣故，使得二次流現象明顯，但在接近水表面處因水面交波的影響使得接近水表面有流速加快的現象，使得不透水式與透水式橋墩保護工的流速剖面形狀均是呈現S形狀的流速剖面現象。

工程人員在量測保護工附近流速時，是量測保護工上游斜坡處的流速，故對此處的一點、二點、三點法與利用積分法求得的平均速度作比較，發現其差異範圍為仍在工程實務上可容許之差異2.3%，若能在工程實務上能更精準的量測到0.2倍、0.6倍和0.8倍水深的流速並加入不同橋墩保護工上之平均比較差異，將更能接近河川保護工上游斜坡處的平均流速。

This study analyzed experimentally the flow passing through bridge pier impermeable protection structure in open channel. The vertical profiles of the velocity are measured at several locations, such as the front, the top, and the rear of the piers. For the bridge pier permeable protection structure, as the result of drag effect the velocity of near the bed is decreased. Both of the protection structure, on top of the riprap and concrete, the velocity at the lower part of the flow is higher than at the upper part. This is possible due to two reasons; the vertical contraction of the bridge pier, and the velocity of the near water surface increased owing to the crossing wave. Furthermore, the profiles of the velocity are appearance as an S shape.

Traditionally, the river velocity measurement is conducted at the front slope of protection structure. Local representative velocities are taken cross the bridge using so-called one-point, two-point, three-point methods, and compared with integration method. We have an allowable variation at 2.3%. If we accurately measure the velocities and increase different allowable variation of bridge pier protection structure, we would receive more correct averaged velocities in a river.

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