Figure 1.

(a) Pictures of bamboo structures built by the Indonesian Ministry of Marine Affairs and Fisheries in Demak, Indonesia. The structures are formed by arrays of bamboo poles with a diameter of $d\approx$ 0.15 m, distributed over a width of approximately 1.5 m in the streamwise direction. Their volumetric porosity ranges between $n\approx$ 0.5 and 0.9. (b) Top view of one of the structures. Both drone pictures are courtesy of S.A.J. Tas. (c) Sketch representing the effects of blockage and sheltering on the local flow velocity (blue arrows) at the scale of the bamboo poles of a structure (solid brown circles), inspired by Etminan et al.¹¹ and Zdravkovich¹². Incoming flow velocities $U_{\infty }$ accelerate to $U_{\mathit{bl}}$ between the cylinders, an effect known as blockage. Behind the first row of cylinders, velocities reduce to $U_w$ due to sheltering effects. The relative magnitude of these effects depends on the streamwise and lateral or spanwise spacing of the cylinders ($s_x$ and $s_y$, respectively).