Abstract: Spur dike with compound section is a common structure used in waterway regulation. In this paper, the law of velocity distribution around non-submerged spur dike with compound section is researched via flume experiment, and the results manifest that I) In surface layer, large resultant velocity appears outside the downstream of the first-stage spur dike head; the length (b₂) of the second-stage spur has noticeable impact on the value and morphological distribution of the zone of large resultant velocity whereas Froude number (Fr) only affects the value of velocity; transverse surface velocity distributes in an approximated fan shape, with the maximum value up to 0.45 times of test velocity. (II) In cross-sectional scale, large longitudinal velocity is located in the adjacent of the head of the first-stage spur dike, and intense transverse velocity zone is in the front of the second-stage spur dike, both distributing in a band shape; with the increase of b₂, the band width declines, and the distribution is more concentrated. (III) In longitudinal profile, the maximum longitudinal velocity is found in the downstream of the spur dike near water surface, and its position moves up along with the increase of b₂; while the transverse velocity increases first and then decreases, with its maximum value arising close to the bottom; intense high transverse velocity zone stretches in a maple leaf shape.The research results provide reference for waterway regulation and spur dike protection.

Key words: non-submerged spur dike, compound section, longitudinal velocity, transverse velocity, distribution law