Maritime or coastal structures can be easily utilized as basement of larvae settlement when they have uneven surface.
　Setlement ratio may be govrned mainly by velocity field near the surface under the same nutrient and environmental conditions. Appropriate uneven configulation
reduces the intensity of surface velocity and makes stagnated area for trapping larvae.
　Hydraulic experinments and numerical simulations were conducted to obtain the basic idea of relationship between attached pipes and the local flow.
　Uneven bads for experiments were constructed by rectangle pies on a flat plate. The flow structure behind the pipes was found to be governed by Reynolds' Number
and pitch between pipes.
　After the numerical simulations, difference of the flow structures was explained by the interaction among released vortices from pipes. The relative location be
tween reattachment point of the released vortrices and pitch of the following pipes took an important role for this interaction.